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Page 1: Bridge Repair Manual

Issue A Australian Rail Track CorporationRevision 1 This document is uncontrolled when printedMarch 2006 Page 1 of 245

Engineering Practices Manual

Civil Engineering

Bridge Repair Manual

RC 4300Issue A, Revision 1

March 2006

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Engineering Practices ManualCivil Engineering RC 4300Bridge Repair Manual

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Contents

Part 1 General .................................................................................................................8

1. Introduction ............................................................................................................9

1.1. The purpose of this manual ......................................................................................9

1.2. Nature of the repair procedure..................................................................................9

1.3. Who should use this manual?...................................................................................9

1.4. Aims of repair procedures....................................................................................... 10

1.5. The structure of this manual ................................................................................... 10

1.6. Format for repair procedures .................................................................................. 10

2. Selecting repair actions ....................................................................................... 11

2.1. Introduction............................................................................................................. 11

2.2. Procedure for selecting repair action ...................................................................... 12

2.3. Testing for and measuring defects.......................................................................... 14

2.4. Engineering assessments....................................................................................... 15

2.5. Avoiding recurrence of defects ............................................................................... 16

2.6. Steel repair issues..................................................................................................16

2.7. Concrete repair issues............................................................................................ 18

2.8. Masonry repair issues ............................................................................................ 18

3. Health and Safety .................................................................................................18

3.1. General .................................................................................................................. 18

3.2. Work Safety............................................................................................................ 19

3.3. Public safety ........................................................................................................... 20

3.4. Health..................................................................................................................... 20

3.5. First aid .................................................................................................................. 21

3.6. Cleaning up ............................................................................................................ 21

3.7. Removal of lead based paints ................................................................................ 22

Part 2 Steel Repairs....................................................................................................... 23

4. Introduction to standard steel repairs ................................................................ 24

4.1. Introduction............................................................................................................. 24

4.2. Selecting the appropriate repair procedure............................................................. 24

4.3. Sub-procedures...................................................................................................... 24

4.4. Avoid welding ......................................................................................................... 24

4.5. Drawings ................................................................................................................ 25

4.6. Repair materials ..................................................................................................... 25

4.7. Health and safety.................................................................................................... 25

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4.8. References............................................................................................................. 25

5. Sub-procedures.................................................................................................... 26

5.1. Arresting corrosion (Sub-Procedure) ...................................................................... 26

5.2. Removing rivets and replacing with bolts (Sub-procedure) ..................................... 27

5.3. Patch painting (including surface preparation) ........................................................ 30

5.4. Filling voids (Sub-procedure).................................................................................. 33

5.5. Sealing interfaces (Sub-procedure) ........................................................................ 35

6. Repairing corroded flanges and webs of girders............................................ 35

6.1. Repairing flange corrosion in riveted girders........................................................... 35

6.2. Repairing flange corrosion in rolled or welded girders ............................................ 39

6.3. Repairing web corrosion near bottom flange angles in riveted girders .................... 41

6.4. Repairing webs with localised corrosion .................................................................45

6.5. Repairing corroded bottom flanges of jack arch bridges ......................................... 47

7. Repairing stiffeners, bracing connections and bearings ..................................51

7.1. Relief of corrosion site at the base of intermediate web stiffeners........................... 51

7.2. Repairing intermediate and bearing web stiffeners with localised corrosion............ 55

7.3. Repairing bearing web stiffeners with localised corrosion at base of outstand leg ofstiffener .................................................................................................................. 61

7.4. Relief of corrosion site at the base of splayed angle bearing end stiffeners ............ 62

7.5. Repairing corrosion at bottom flange bracing connection........................................ 64

7.6. Replacing bearing plates ........................................................................................ 68

7.7. Repairing cracked and broken wind brace welded connections .............................. 73

8. Repairing fatigue damage.................................................................................... 74

8.1. Intercepting fatigue cracks...................................................................................... 74

8.2. Repairing fatigue cracks at connections of coped I-sections...................................76

9. Repairing impact damage .................................................................................... 78

9.1. Description of Defect .............................................................................................. 78

9.2. Engineering Discussion .......................................................................................... 79

9.3. Sub-procedures required........................................................................................ 79

9.4. Procedure outline ...................................................................................................80

10. Repairing stepways and footways structures .................................................... 87

10.1. Repairing steel risers and stringers in stepways ..................................................... 87

10.2. Repairing corroded angle colums ........................................................................... 93

10.3. Repairing corroded 4-angle colums ........................................................................ 96

11. Complete replacement of members .................................................................. 102

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11.1. Replacing members or elements of riveted members ........................................... 102

12. Introduction ........................................................................................................ 105

12.1. General ................................................................................................................ 105

12.2. Health and safety.................................................................................................. 105

12.3. References........................................................................................................... 105

13. Deterioration of concrete ................................................................................... 105

13.1. Factors affecting deterioration .............................................................................. 105

13.2. Causes of deterioration ........................................................................................ 106

14. Types of defects ................................................................................................. 113

14.1. Introduction........................................................................................................... 113

14.2. Cracking ............................................................................................................... 113

14.3. Spalling ................................................................................................................ 116

14.4. Scaling ................................................................................................................. 117

14.5. Delamination ........................................................................................................ 118

14.6. Leaching............................................................................................................... 118

14.7. Rust stains............................................................................................................ 119

14.8. Honeycombing ..................................................................................................... 119

14.9. Dampness ............................................................................................................ 120

14.10. Leaking joints................................................................................................... 120

14.11. Breaking up of repairs...................................................................................... 120

15. Assessment of deterioration ............................................................................. 120

15.1. General ................................................................................................................ 121

15.2. Assessment procedures ....................................................................................... 121

15.3. Other detection methods ...................................................................................... 123

16. Repair materials.................................................................................................. 123

16.1. Introduction........................................................................................................... 123

16.2. Material properties................................................................................................ 124

16.3. Types of Repairs .................................................................................................. 124

16.4. Questions to consider before choosing a repair material ...................................... 137

17. Repair options .................................................................................................... 139

17.1. Establish need for repairs ..................................................................................... 139

17.2. Repair options ...................................................................................................... 139

17.3. Selection of repair methods .................................................................................. 139

18. Introduction to concrete repair procedures ..................................................... 140

18.1. General ................................................................................................................ 140

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18.2. Repair methods .................................................................................................... 140

18.3. Sub-procedures.................................................................................................... 140

18.4. Steps in repair work.............................................................................................. 140

19. Sub-procedures.................................................................................................. 141

19.1. Removing damaged concrete (sub-procedure)..................................................... 141

19.2. Removing concrete at joints (Sub-procedure)....................................................... 143

19.3. Cleaning concrete substrate for patch repairs and re-casting (sub-procedure) ..... 145

19.4. Cleaning Concrete Surface for Overlays............................................................... 145

19.5. Cleaning reinforcement (Sub-procedure).............................................................. 146

19.6. Adding reinforcement (Sub-procedure)................................................................. 146

19.7. Applying bonding coat to concrete (Sub-procedure) ............................................. 147

19.8. Coating reinforcement (Sub-procedure)................................................................ 148

19.9. Formwork for re-casting concrete (Sub-procedure)............................................... 148

19.10. Curing (Sub-procedure) ................................................................................... 149

19.11. Surface preparation for external coatings (Sub-procedure) .............................. 150

20. Repairing cracks................................................................................................. 151

20.1. Types of cracks .................................................................................................... 151

20.2. Repair methods for cracks.................................................................................... 151

20.3. Cracks that should be repaired ............................................................................. 152

20.4. Epoxy injection ..................................................................................................... 153

20.5. Grouting ............................................................................................................... 154

20.6. Routing and sealing.............................................................................................. 155

20.7. Drilling and plugging ............................................................................................. 156

20.8. Stitching ............................................................................................................... 157

20.9. Adding reinforcement ........................................................................................... 158

20.10. Surface treatments........................................................................................... 160

20.11. Flexible sealants for live cracks........................................................................ 161

21. Patch repairs....................................................................................................... 163

21.1. Engineering discussion......................................................................................... 163

21.2. Repair procedure with cement-sand mortars ........................................................ 163

21.3. Repair procedure with polymer modified cementitious mortars ............................. 164

21.4. Repair procedure with epoxy mortars ................................................................... 164

22. Recasting with concrete .................................................................................... 165

22.1. Engineering discussion......................................................................................... 165

22.2. Concrete mix design............................................................................................. 166

22.3. Repair procedures................................................................................................ 168

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22.4. Replacing bearing pads........................................................................................ 169

23. Repairs for corrosion ......................................................................................... 170

24. Sprayed concrete ............................................................................................... 170

24.1. Repair procedure.................................................................................................. 171

25. Protective coatings ............................................................................................ 172

25.1. Engineering Discussion ........................................................................................ 172

25.2. Repair procedure for chloride build up.................................................................. 173

25.3. Repair procedure for carbonation ......................................................................... 174

26. References.......................................................................................................... 175

27. Introduction to masonry repairs........................................................................ 179

27.1. General ................................................................................................................ 179

27.2. Health and safety.................................................................................................. 179

27.3. Acknowledgements .............................................................................................. 179

28. Deterioration of Masonry ................................................................................... 179

28.1. Causes of deterioration ........................................................................................ 179

29. Types of defects ................................................................................................. 182

29.1. Cracks .................................................................................................................. 182

29.2. Fretting ................................................................................................................. 183

29.3. Spalling ................................................................................................................ 183

30. Assessment of deterioration ............................................................................. 183

30.1. General ................................................................................................................ 183

30.2. Assessment procedure......................................................................................... 183

31. Repair materials.................................................................................................. 185

31.1. General ................................................................................................................ 185

31.2. Function of mortar ................................................................................................ 185

31.3. Problems with strong mortars ............................................................................... 185

31.4. Importance of lime in mortars ............................................................................... 186

31.5. Basic principles .................................................................................................... 186

32. Methods of repair ............................................................................................... 186

32.1. General ................................................................................................................ 186

32.2. Steps in repair work.............................................................................................. 187

32.3. Strength and stability ............................................................................................ 187

32.4. Repairs of cracks.................................................................................................. 187

32.5. Fretting ................................................................................................................. 189

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32.6. Impact damage..................................................................................................... 191

32.7. Corrosion of embedded iron or steel..................................................................... 191

32.8. Miscellaneous repairs........................................................................................... 191

Appendix A Repair materials ...................................................................................... 193

Appendix B Guidelines for Management of Lead Paint on Steel Structures........... 196

Appendix C Guidelines for welding old steels .......................................................... 231

Appendix D Techniques for removing rivets using oxy-fuel equipment ................. 244

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Bridge Repair Manual

Part 1General

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1. Introduction

1.1. The purpose of this manual

The purpose of this manual is to describe and detail standard repair procedures fordefects commonly found in bridges owned and maintained by ARTC. Both newprocedures and those that have been previously used successfully on ARTC'sbridges are included.

Several advantages result from standardising repair procedures:

The standard repair procedures included have been developed to be bothstructurally sound and practically achievable. Adherence to standard repairprocedures reduces the incidence of inappropriate and ineffective repairsand repairs that have adverse effects on the bridge.

Repairs will be undertaken in a consistent fashion throughout ARTC, whethercarried out by day labour or under contract.

The engineering input into detailing sound repairs is minimised andduplication of effort in developing repair procedures is avoided.

The cumulative knowledge and experience gained in carrying out repairs canbe incorporated into the repair procedures and details. This is an effectivemeans of passing on the knowledge.

Relevant engineering information about the repair procedures is included inthe manual to assist those responsible for selecting appropriate repair action.

1.2. Nature of the repair procedure

The repair procedures given are generic in nature; that is, they apply to a range ofsimilar solutions, with varying member size, position and arrangement. As such it isnot possible to completely detail the repair. Additional information such as the sizeand connections of strengthening elements and their precise position needs to besupplied to enable the repair to be completed.

Notwithstanding the above, guidelines for the selection of size, position andconnections of strengthening elements etc, are given wherever possible to minimisethe amount of engineering input required. Such guidelines are often conservativeand savings may be made in materials and labour requirements for the repair if theengineering details of the repair are determined by design for the specific case athand. The savings may be significant and worthwhile if the extent of repair is great.

1.3. Who should use this manual?

This manual should be used by those responsible for:

selecting repair actions for bridges;

implementing repairs either using day labour or under contract;

inspecting repair work carried out by either day labour or

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contractors;

carrying out routine or special maintenance on bridges that have beenrepaired.

1.4. Aims of repair procedures

The aim of the repair procedures is to restore the strength and serviceability of thebridge structure, either to the "as new" condition, or to the condition that is requiredfor current or envisaged use.

In developing repair details the normal design practices, as specified in theAustralian Bridge Design Code, are applied. It is reasonable that there will be thesame level of confidence in the repaired bridge as in a new structure. For steelstructures, the fatigue life of the repaired bridge should not be less than the life thatwould have remained had the defect not occurred.

Some of the repair procedures, such as concrete etching, aim to restore the originalintegrity of the member. Other repairs, typically when used in steel structures, aim tocompensate for the defect by the attachment of additional structural elements.

A few procedures that are included are not repairs as such, but rather actions thatcan be taken to reduce or arrest further deterioration of the structure, or make thestructure easier to maintain.

1.5. The structure of this manual

The manual is divided into five parts.

Part 1 provides an introduction to the manual, discusses the process ofselecting repair actions and presents information on environmentalsafety and occupational health as related to bridge repairs.

Part 2 covers standard repairs to steel bridges.

Part 3 covers standard repairs to concrete bridge superstructures andsubstructures.

Part 4 covers repairs to masonry.

Part 5 covers repairs to timber bridges. (not yet written)

Additional information such as specifications for repair materials and furthertechnical information are included in the Appendices.

1.6. Format for repair procedures

Each repair procedure is presented in a consistent format comprising the followingparts.

1. Description of defect.

2. Description of repair.= A brief statement describing the form of the repair.

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3. Engineering discussion.= A discussion of engineering aspects of the repair.

4. Sub-procedures required.

5. Procedure outline.= The main steps in implementing the repair are described. This is to beread in conjunction with drawings detailing the repair. Separate procedureoutlines may be given for different cases.

6. Alternative details.= Describes possible alternatives to part, or all, of the repair.

7. Action to avoid recurrence.= Describes action that can be taken to avoid or minimise recurrence of thedefect.

8. Special considerations and effects of repair.= Describes special considerations required, such as traffic restrictions, oreffects of the repair on the structure.

9. Follow-up inspection and testing.= Indicates requirements for follow-up inspection or testing to confirm theongoing performance of the repair.

10. Drawing List.= Lists the drawing(s) that describe and detail the repair.

Some of these parts are omitted if they are not relevant.

2. Selecting repair actions

2.1. Introduction

The aim of repairing a bridge is to extend its life. It is most important that the repairactions selected satisfy this aim at a cost commensurate with the benefits derived.Inappropriate repair action may actually reduce the life expectancy of a bridge. It isalso possible that money spent on extensive and costly repair will not extend the lifeof the bridge significantly and would be better put towards a new bridge.

Selection of appropriate maintenance, rehabilitation and replacement (MR & R)actions for a bridge is part of the function of a Bridge Management System. Theprinciples of Life Cycle Costing are applied in Bridge Management Systems todetermine the optimum MR & R strategy that will result in minimum annual cost ofproviding a bridge at a site.

If a Life Cycle Costing analysis cannot be carried out, the next best thing is todetermine the appropriate repair action by applying a process of logical assessmentto the bridge as a whole.

Section 2.3 below presents a series of questions to be considered in the process ofselecting appropriate repair action.

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2.2. Procedure for selecting repair action

In determining the appropriate repair action to be carried out on a bridge, thefollowing questions should be answered:

2.2.1 What is the nature, severity, location and extent of each defect?

To enable a considered logical assessment of repair actions, full data about eachdefect must be known and recorded from site inspections, measurements andtesting. Clause 2.3 deals with testing for and measurement of defects.

2.2.2 Is a repair to restore full strength necessary?

The underbridge, overbridge, footbridge or stepway may have been designed with aload capacity greater than currently required or envisaged. In this case the strengthreduction caused by the defect may be acceptable.

Even if the full design load capacity is needed, a small overstress say 10% -resulting from the defect can usually be accepted.Some elements may be able to tolerate considerable deterioration before repair orstrengthening is needed. For example, the full flange area of a rolled girder may notbe necessary near the end of a span where the bending moment is small.

The necessity for and extent of a repair should be determined, where appropriate,by a full engineering assessment. The time and effort required for such a task maybe repaid by minimising the extent of repairs needed or by determining that therepairs are not structurally necessary. Clause 2.5 discusses the role of engineeringassessments.

If it is found that repair or strengthening is not needed, then the only actionrequirement is to protect the structure from further deterioration.

The serviceability requirements, particularly fatigue in steel, should be considered ina similar manner to strength.Note that a repair may be warranted to improve the appearance of a bridge, even ifit is not structurally essential.

2.2.3 Is a standard repair procedure available for each defect?

It is not normally appropriate to repair one defect in a bridge if other signifiantdefects are left unrepaired because satisfactory or cost effective repair proceduresare not available.

It should be confirmed that a standard repair procedure envisaged is actuallyappropriate to the defect. The engineering discussion accompanying each repairprocedure will describe where the procedure should and should not be used.

2.2.4 What is the total cost of repairing all defects?

The total cost of repairing all defects in a bridge, even if only determined crudely,should be estimated and compared with the expected benefits. The benefits areusually either extending the life of the bridge or eliminating an immediate dangeroussituation. The costs of any track possessions etc. that are required should beincluded.

If the costs of repair are substantial and the repairs are non-urgent for safety, then it

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may be better to replace the bridge and divert repair funds to more appropriatecases.

The initial cost estimate will be a factor in deciding if a detailed engineeringassessment is worthwhile. When the total cost is high say more than 5% to 10% ofthe bridge replacement cost -a detailed engineering assessment must be carriedout. The extent of repair is likely to be minimised as are sizes and numbers ofconnections for strengthening elements.

2.2.5 How significant will the repair be in extending the life of the bridge?

The proposed repair may not provide value for money if the life of the bridge is notextended because of other factors.

Most steel bridges have a finite life, governed by fatigue of the steelwork. It may notbe appropriate to spend large amounts of money on repairs if the bridge is near theend of its predicted fatigue life. Replacement is probably a better option.

In concrete structures, defects such as corrosion of reinforcement may not beapparent at the present time, but the effects may show up in the form of concretecracking and spalling in the near future. It may not be appropriate to spend moneyon repairing some localised defects if much more extensive defects are likely toshow up in the near future. Investigation by specialists into the complete structuremay be warranted prior to undertaking costly repairs of concrete.

As another example, the benefits of repairing corroded bottom flanges of jack archbridges may not be certain because the condition of the remainder of the steelsection is usually not known. The effort in repairing the bottom flange would bewasted if the top flange and web were also severely corroded.

2.2.6 Can the cost of the repair be justified on the basis of benefits derived?

The answer to this question will normally be evident from the answers to questions2.2.2 to 2.2.5. For some bridges there may be additional factors that influence thedecision on whether to implement a particular repair.

Taking advantage of planned track possessions may often be a significant factor indeciding whether to implement a repair or not. In many repairs, particularly smallerones, the cost of the track possession is the major component. If the repair can becarried out under a possession provided for other reasons, the actual cost of therepair drops significantly for the same benefit. A repair that could not normally bejustified on a cost/benefit basis may become cost effective as a result.

2.2.7 Is a detailed engineering assessment needed?

The reasons for, and benefits of, an engineering assessment are discussed in Part 2Section 2.4 of this manual. The decision to undertake an engineering assessmentwill be based on the cost of the assessment versus the possible benefits.

A longer lead time to implement a repair will usually be required if an engineeringassessment is to be undertaken.

2.2.8 Has partial replacement of the bridge been considered?

As an alternative to repairing defects or strengthening members, considerationshould be given to partial replacement of the structure.

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This may involve merely replacement of damaged bracing members, stiffeners,stringers, cross girders etc. up to complete replacement of main girders.

The decision will be based on time, cost and effectiveness of the repair compared tothat of a complete replacement. If the effectiveness or life expectancy of repairs orstrengthening is limited, then complete replacement of an element may be a betteroption, particularly if the cause of the defect can be eliminated at the same time.

2.2.9 Will the repair have any adverse effects on the structure?

Consider any adverse effects that the repair may have on the performance of thebridge.

Will traffic clearances be reduced?

Will the structure become more vulnerable to damage or deterioration?

Will other potential defects be hidden by the repair?

2.3. Testing for and measuring defects

2.3.1 General

As stated in 2.2.1 above, it is necessary to determine the nature, severity, extentand location of defects to determine appropriate repair actions. Most defects areinitially detected by visual inspection. The severity, extent and location aredetermined by subsequent measurements and tests.

2.3.2 Measuring section loss in steel

In steel structures, corrosion of steel leading to a loss of section is a common defect.Measurements are to be taken to determine the thickness of remaining sound steelfor comparison with the original thickness. All loose rust and corrosion product mustbe removed at the point of measurement to allow an accurate reading. Verniercalipers or preferably a micrometer should be used to obtain accuratemeasurements to at least an accuracy of ± 0.25mm.

The number and location of measurements required will depend on the defect underconsideration. Usually the minimum requirement is to measure the remaining cross-sectional area of an element (flange, web, stiffener) at the location of the greatestcorrosion loss and location of greatest stress.

2.3.3 Testing for and measuring cracks in steel

Although many cracks in steel can be detected by visual inspection, it is usuallynecessary to use techniques such as magnetic particle testing to determine theexact extent of cracks. This is particularly important in mapping fatigue cracks wherethe end point must be found.

Examination for cracks and other defects in new welds will require the use of non-destructive techniques such as ultrasonic or X-ray examination.

Further discussion of N-D examination methods is beyond the scope of this manual,but reference is made to the appropriate Australian Standards.

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2.3.4 Observation under load

The severity of some defects is best determined by observing the structure duringthe passage of a heavy load. Loose rivets and bolts may be detected by thismeans. The behaviour of girder bearing plates and bed plates under load will aid indetermining the necessity for repair or replacement.

2.3.5 Detecting defects in concrete

While most defects in concrete, such as cracking, spalling and rust staining aredetected by visual examination, the likelihood of further deterioration can bedetermined using specialist testing techniques. Tests to determine extent ofcarbonation, chloride penetration, cover to reinforcing etc. can be carried out todetermine the life expectancy of concrete. As outlined above, this information isuseful in planning the long term maintenance and repair strategy for a concretestructure.

Refer to Part 3 of this manual, dealing specifically with concrete repairs, for moreinformation on testing of concrete.

2.4. Engineering assessments

An engineering assessment or investigation into a proposed repair must be carriedout and is essential to determine the appropriateness of the repair and the repairdetails. The engineering assessment is based on measured and recorded defectsfound on the bridge during inspections, the structural drawings of the bridge and theload capacity requirement of the bridge.

The aims of an engineering assessment are to:

• determine the effect of the defects on the strength of the structure,

• determine the effects of the defects on the serviceability of the bridge,including its fatigue performance,

• determine or confirm that each proposed standard repair is both necessaryand suitable to address the defect,

• determine the extent of all the required repairs,

• determine the engineering details of the repairs where required these includeplate sizes, fastener sizes and types, new connection details etc.

A detailed engineering assessment is not always required. The repair proceduresinclude, where possible, guidelines for determining the above data, albeit adopting aconservative approach. A detailed engineering assessment is required where theestimated total cost of repairs is more than 5% to 10% of the replacement cost ofthe structure. In such cases, the cost of the investigation could be more than savedin the reduced extent of repair.

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2.5. Avoiding recurrence of defects

In conjunction with carrying out the repairs, action should be taken where possible toavoid recurrence of the defects. This has been considered in devising repairprocedures. To protect against recurrence of the defect, the original cause must beknown and eliminated where possible.

The causes of defects are often built into the structures and are difficult to eliminate.Deterioration of concrete, for example, due to insufficient cover to reinforcing or poorconcrete compaction, cannot be easily addressed. Details in steel structures whichare prone to corrosion because of collection of water and dirt cannot be readilyeliminated without changing the structure significantly.

Often the only effective means of avoiding recurrence of the defect is preventivemaintenance of the structure to remove dirt and debris and to maintain the integrityof the paint system.

Where possible galvanised strengthening or replacement elements should be usedto ensure long term corrosion protection with minimum maintenance requirements.The standard repair procedures specify galvanised elements where possible.

2.6. Steel repair issues

2.6.1 Methods of connection

In addressing defects in steel bridges resulting from steel corrosion, it is clearly notpossible to reinstate the steel to its original condition. Similarly, restoring physicallydamaged steel to its original condition is often difficult. Most repairs therefore involvefitting new steel elements to compensate for the reduction in strength orserviceability caused by the section loss.

The two standard methods of connecting new elements are welding and mechanicalfastenings (bolts etc.). Of the two, mechanical fastenings have the least potentialproblems although welding is usually easier and cheaper. Mechanical fastenershave been adopted as the standard method in all steel repair procedures.

The two main potential problems with field welded connections are:

1. satisfactory welds may be difficult or impossible to achieve in steels of olderbridges because of their metallurgical properties; and

2. the fatigue life of the structure may be adversely affected by welding. Theeffect may be severe.

Refer to 2.6.2 and 2.6.3 below.

Connection by welding can only be permitted if satisfactory welds are proven to beachievable and any effects on fatigue life are acceptable. Most standard repairs,detailed with bolted connections, can be readily adapted for welded connections.

2.6.2 Weldability of steel

While modern steels can be readily repaired by welding using appropriateprocedures, the steels found in older steel bridges are often considered "not

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weldable" or very difficult to weld because of their metallurgical properties. The highsulphur and phosphorous contents largely contribute to difficulty in welding.

Unfortunately, it is not possible to classify steels as weldable or "not weldable"based on their age. From the 1940's to the 1960's some imported steels were fromplants producing steels designed to be weldable, while others were from plantsproducing unweldable steels.

It is essential that, where a welded repair is proposed on steels of unknownweldability, the steels be tested to determine whether or not they are weldable bynormal welding procedures. The necessary tests can be carried out by NATAAccredited Laboratory.

It is sometimes technically possible to achieve satisfactory welds in older style (non-weldable) steels, but only by careful adherence to particular welding proceduresdesigned for such steels. A high level of operator skill and good welding conditionsare required. Unfortunately, most steel repairs must be carried out in conditionswhich are anything but conducive to good welding.

Appendix C provides details of techniques for welding so-called "nonweldable"steels. The information is intended for accredited welders/boilermakers alreadyskilled in normal welding techniques. If such welding is attempted, it is essential tocarry out test welds to confirm that acceptable results can be achieved under siteconditions. It is also necessary to carry out non-destructive testing of the completedwelds to confirm their integrity.

Also, careful consideration must be given to the ramifications of a failed attempt at awelded repair on "non-weldable" steels. The cost of undoing the damage may besignificantly greater than if a bolted connection repair had been carried out.

2.6.3 Effect on fatigue life

As in the design of new steel bridges, the details of welded connections used insteel repairs may have an effect on the fatigue life of a bridge. Although theremaining life of a bridge that has been in service for many years is not expected tobe as great as a new bridge, it is best to avoid any repair actions that wouldadversely affect fatigue life. This is particularly so if viable bolted connectionalternatives are available.

Properly maintained riveted girder bridges with low stress levels may never fail byfatigue. Repairs involving welded connections on such bridges often set a finitefatigue life and so should be avoided.

If a welded repair is proposed, it should always be accompanied by an engineeringassessment of the effect on the fatigue life of the weldment. The AREA Manual forRailway Engineering should be used to assess the effects. The proposed weldedrepair should only be implemented if the effects on fatigue life are acceptable.

2.6.4 Redundancy of riveted girders

Riveted girders, comprising multiple elements for flanges, have beneficialredundancy that should not be removed by the repair process. Redundancy meansthat if one of the plate or angle elements of a flange fails, say by a fatigue crack, thewhole girder will not immediately fail as the fatigue crack cannot propagate to otherelements. Inspection can detect the failed component for repair prior to complete

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failure of the girder. The stress levels in the uncracked elements obviouslyincrease, causing overstress and reducing the overall fatigue life, but the situation isbetter than in welded or rolled girders where a crack in a flange can quicklypropogate all the way through the section, leading to collapse.

The elements of riveted girder flanges must not be joined by welding as this wouldcreate paths to allow fatigue cracks to propagate from one element to another.

Redundancy is of particular benefit in bridges of a considerable age because itprovides a degree of protection against sudden failure. The redundancy must bepreserved.

2.7. Concrete repair issues

The most important issue in the repair of any structure is to ensure adequatestrength and stability at all times. This is particularly relevant in repair to reinforcedconcrete elements where significant areas of concrete are to be removed. In suchcases the strength or stability of the structure with the concrete removed should bechecked by a structural engineer before commencing repairs. Also, load restrictionsshould be applied and the structure temporarily supported as necessary.

The repair of concrete structures requires a knowledge of the following issues:

1. Types of defects which can occur due to deterioration, e.g. cracks, spalls,delamination, scaling, honeycombing etc.

2. Causes of deterioration, e.g. chloride penetration, carbonation, alkali -aggregate reaction, shrinkage and thermal effects, foundation movementsetc.

3. Test methods for assessing the severity of deterioration.4. Selection of appropriate repair materials, from ordinary Portland cement to

synthetic polymers, resins and acrylics according to particularrequirements of a repair project.

5. Selection of appropriate repair procedure.

Part 3, Concrete repairs, contains detailed discussion of all the above issues.However, it does not include complex and advanced repair methods such ascathodic protection, re-alkalisation etc., which should only be entrusted toorganisations specialising in this work.

Also, the repair methods are for reinforced and plain concrete only, not prestressedconcrete.

2.8. Masonry repair issues

The repairs of masonry structures generally involve the same issues as for concretestructures. Methods and materials for masonry repairs are included in Part 4.

3. Health and Safety

3.1. General

For the protection and safety of workmen, public and environment, safe workpractices are essential on every work site. The following safety aspects are

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common to most types of ARTC work and must be considered prior tocommencement of any construction or repair project:

Work safety Public safety Environmental safety Health

Health and safety have a high priority at all times during field operations. Allstatutory rules and regulations under various Occupational Health and Safety Actsand safety practices detailed in ARTC’s Safety Management System are for guidance in planning for safety at all the worksites. Commonsense should be usedin anticipating the particular safety requirements for each and every project to beundertaken.

3.2. Work Safety

Work safety must be planned ahead. Before commencing work the supervisorneeds to attend to the following:

1. Familiarise yourself with full requirements of the repair work includingformwork, falsework, demolition, repair materials, repair method, and safetyrequirements of handling repair materials and equipment.

2. Arrange personnel who are skilled in the particular type of repair.

3. Ensure that all tools, plant and equipment are available and in good workingorder.

4. Arrange all repair materials including materials necessary for cleaning toolsand plant after completion of work.

5. Arrange safety harnesses, clothing, footwear, gloves, ear muffs, eyeprotection glasses, masks, helmets, welding shields, and any other itemsnecessary for personal safety of the workers. Supply washing soap, towelsand barrier creams for worker hygiene.

6. Identify and locate all the utilities existing at site, such as water, sewerage,electricity, signals, communications, gas etc. If any utilities are affected bywork take measures in advance to protect them or get them relocated asnecessary through appropriate authorities. If any risk is foreseen, inform theauthorities to stand by for any emergencies.

7. Ensure that first aid equipment is available at site and that at least one of thepersonnel at site holds a valid qualification for giving first aid.

8. If necessary, plan and arrange for standby oxygen administering equipmentand fire-extinguishers. Under such circumstances workers should be trainedbeforehand in how to use them.

9. All work must be carried out in well ventilated and well lit areas. If necessarymake prior arrangements for exhaust fans and artificial lighting.

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10. If scaffolding and falsework are required for supporting the structure, arrangethis to be designed by qualified structural engineers. Erection and stability offalsework must be supervised by qualified technical persons.

11. Persons who are not qualified for carrying out a particular task or operating aparticular equipment must not be allowed to do that task or operate theequipment.

12. Generally, all the work should be carried out as per industry's normalstandards of practice and/or in compliance with the Australian Standards.

13. All repair work using proprietary materials must be carried out strictlyaccording to the manufacturer's printed instructions. The manufacturer'sproduct data sheets for health and safety precautions must be carefully readand followed.

3.3. Public safety

There are legal obligations to take all necessary precautions and adequatemeasures for safety of public in and around the working area. The following stepsshould be taken to safeguard the public against any injury, loss of life or property:

1. Attend immediately to any damage and deterioration which may cause lossof strength and stability of a structure and thereby may result in injury, loss oflife or property to public.

2. Take steps to support the structure against instability and collapse, as wellas protect the adjacent properties, plant and utilities from possible damage.

3. Until the structure is made safe, close off access to it and prohibit its use bythe public by setting up suitable fences and barriers. With the assistance ofpolice and Road and TrafficAuthority arrange to divert the pedestrian and vehicular traffic by alternativeroutes. Provide warning signs and hazard lights as necessary to caution thepublic of danger.

4. During progress of the work, take all necessary precautions to safeguard thepublic from suffering excessive hardship and inconvenience which may becaused by equipment, materials and procedures. Minimise noise, dust,flooding, blowing of sand and grit in blasting operations, toxic fumes, debrisand so on.

5. At the completion of the repairs, clean up all dirt and debris, remove all plant,equipment and materials and restore the facility to public.

Caution:In construction and repair work on railway sites, use is frequently made ofexplosives, detonators and hazardous materials. The issue and use of suchmaterials must be strictly controlled. Particularly, all explosives and detonators mustbe accounted for in order to prevent their falling into hands of children andundesirable elements. Many a loss of life and limb has been caused by detonatorspicked up by children and adolescents and used for "fun".

3.4. Health

All personnel engaged at a work site must be protected against sickness andpersonal injury caused by work conditions, repair materials and methods of repair.Accidents, injury and sickness can be minimised by taking the following precautions:

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1. Do not work in unventilated or poorly ventilated areas. Many repairmaterials and procedures give off unpleasant vapours or toxic fumes thatcan cause nausea or breathing difficulties. If necessary, wear respiratormasks. Do not smoke while working, as you may inhale vapours andfumes too.

2. Handling of polymers, epoxies, acrylics and other cementitious materialsoften causes skin and eye irritations. Before mixing and using thesematerials, read all label warnings on the packages as well as themanufacturers’ product literature and follow the handling instructions carefully. Avoid physical contact with the materials by wearing protectiveclothing, shoes, gloves and protective eye wear at all times.

3. Apply protective barrier cream on exposed skin. (However, do not usebarrier creams as substitute for protective clothing).

4. If any material comes into contact with skin or enters the eyes, give first aidimmediately, as described herein later.

5. If overalls or inside of shoes and gloves become contaminated, removethem as soon as practicable and replace them with clean ones.

6. Wash thoroughly with warm soapy water before eating, drinking or smokingand after finishing work.

3.5. First aid

The following first aid procedures should be followed:

EyesIf any material enters the eyes or irritation persists, hold eyes open, flush with lowpressure water for at least 10 minutes and seek immediate medical aid.

SkinIf skin contact occurs, remove contaminated clothing and wash skin thoroughly withwarm soapy water. If irritation persists or skin rashes or allergic responses such aswheezing and swelling occur, seek immediate medical aid.

InhalationPersonnel affected by inhalation of vapour etc. should be removed from thecontaminated area into fresh air. Apply artificial respiration if not breathing and seekimmediate medical aid.

IngestionImmediately rinse the mouth repeatedly with water. If swallowing occurs, do notinduce vomiting. Drink plenty of water and seek immediate medical aid.

FireUse a fire extinguisher appropriate to the type of burning material. Avoid breathingproducts of combustion.

3.6. Cleaning up

All leaks or spillages should be cleaned up as they occur and before they set. Thematerial should be soaked up in suitable absorbents such as dry sand or sawdust,or swept up if it is powdered material. The material should be disposed of quicklyand safely into waste drums.

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Tools and equipment can be cleaned with proprietary solvents or warm water anddetergent before the adhesive has had time to set.

3.7. Removal of lead based paints

The large majority of rail bridges are primed with red lead primer. Lead in any formis toxic to humans and animals when ingested or inhaled.

Particular attention therefore must be paid to environmental safety and worker andpublic health and safety in the process of removing lead based paints. Reference ismade to Appendix B containing the "Guidelines for Management of Red Lead Painton Steel

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Bridge Repair Manual

Part 2Steel Repairs

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4. Introduction to standard steel repairs

4.1. Introduction

Part 2 of this manual gives details of standard repair procedures for defectscommonly occurring in steel bridges and other structures within the ARTC system.Documenting standard repair procedures assists in ensuring that common defectsare repaired in a consistent and structurally satisfactory manner by both ARTC staffand sub-contractors.

It must be emphasised that the information given on each repair is not a fullspecification (in the contractual sense) but a description of the form of the repair andthe steps required to implement the repair for each generic type of defect.Additional information, such as size and thickness of plates, numbers andarrangement of new bolts, extent of repair etc. must be determined by anengineering assessment and provided to the repairer in conjunction with informationin this manual. Guidelines for determining this additional information are given withthe procedure, where possible.

4.2. Selecting the appropriate repair procedure

Chapter 2 of Part 1 deals with selecting the appropriate repair actions or strategiesfor the bridge, looking at it as a whole. Reference is made to that section.

Because of the generic nature of some of the repair procedures given, it is alsonecessary to ensure that the procedure proposed is appropriate and applicable forthe particular defect. Careful engineering assessment of the defects, on a case bycase basis, is strongly recommended to assist in ensuring that the appropriate repairprocedure is selected.

Discussion of the engineering considerations of each repair is given within theprocedure. Where appropriate, the discussion includes guidelines for determiningthe necessity for the repair based on the severity of the defect.

4.3. Sub-procedures

Some actions in the repair process are common to more than one repair procedure.For example, the process of replacing a rivet with a high strength bolt is to becarried out in many of the repair procedures. These actions or sub-procedures aredescribed and detailed in Chapter 5.2. Required sub-procedures are referred to inthe main repair procedures.

4.4. Avoid welding

The repair procedures presented generally use bolted connections instead of sitewelding for the following reasons:

High quality site welds are difficult to achieve.

Many of the repairs are to be carried out on old bridges in which the steelsare considered unweldable.

The addition of weldments to members with calculable stresses can oftenreduce the fatigue life significantly.

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Welded repairs can remove or reduce the inherent structural redundancy ofbuilt up riveted sections.

Alternative connection details involving site welding may be possible butshould only be implemented after:

carrying out a full engineering investigation of the effects on strength, fatiguelife and degree of redundancy; and

determining by analysis and tests that site welding the existing steels isachievable and practicable.

Refer to Chapter 2 of Part 1 for more information on the suitability of site weldedrepairs.

4.5. Drawings

Each repair procedure is detailed on one or more drawings. It is envisaged thatthese drawings, together with the text of the procedure outline and the additionalinformation from the engineering assessment referred to in 4.1, will provide all theengineering detail required by site personnel to implement the repair.

As the drawings often include several alternative details, instructions on whichalternative to use may also be required.

4.6. Repair materials

In the repair procedures, repair materials are referred to by their generic name.Specific brand and material names of epoxies, paints etc. are usually avoided asavailability may vary from time to time and new, superior materials may becomemore appropriate. Lists of suitable brand and material names are given in AppendixA, together with the specifications for standard repair materials such as steel andhigh strength bolts.

Where new steel parts are to be fitted as part of the repair, it is generallyrecommended that those parts be galvanised. Use of galvanised steel can reducelong term maintenance requirements and minimise the amount of on-site paintingrequired. Where the appearance of galvanised steel is not acceptable, and paintingover galvanised surfaces is impractical, the steel parts may be painted instead usingone of the high quality paint systems used in bridge repainting. Refer to sub-procedure 5.3 for further information.

4.7. Health and safety

Attention is drawn to Chapter 3 of Part 1 on "Health and Safety" which highlights theprecautions required when handling specialised and hazardous materials duringmaintenance and repair work.

4.8. References

The following references were used in the preparation of Part 2 -Steel Repairs.

1. Australian Bridge Design Code

2. AREA Manual for Railway Engineering

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3. AS4100-1990 Steel Structures

4. AS1252-1983 High Strength Steel Bolts with Associated Nuts andWashers for Structural Engineering.

5. Bridge Fatigue Guide - Dr J W Fisher - AISC New York 1977

6. Guidelines for Evaluation and Repair of Damaged Steel BridgeMembers - National Co-operative Highway Research Program Report271.

7. Importance of Redundancy in Bridge - Fracture Control. R R P Sweeny- Canadian National Railways.

5. Sub-procedures

5.1. Arresting corrosion (Sub-Procedure)

5.1.1 Description of action

Any action that will prevent further deterioration and loss of section in steel due tocorrosion.

5.1.2 Engineering discussion

Arresting of corrosion may be the only repair action that is required or possible for abridge, or it may be required in conjunction with other repair actions. The mosteffective method of arresting corrosion is abrasive blast cleaning followed by thecorrect application of a high quality paint system and its ongoing maintenance.

If that form of corrosion arrest is appropriate, refer to sub-procedure 5.3, patchpainting, for information on preparing for and carrying out patch painting. Note thatthe use of so called "rust converters" prior to painting is not permitted.

In addition to painting, action can be taken to avoid conditions which promotecorrosion. Action to avoid collection and entrapment of water may be worthwhile. Insome locations, holes may be drilled to allow water to drain away. Voids anddepressions which catch water may be filled with epoxy. Epoxy fillers may also beused to profile a surface to promote free drainage of water. Advice on appropriateepoxies should be sought from the recognised manufacturers. Epoxies should bedurable, paintable, and should bond adequately to the substrate. Epoxy with someflexibility may be appropriate for the purpose described.

Denso Tape covering of steel elements may be a suitable alternative to painting.Denso tape could be used at the interface between concrete and steel or timber andsteel. These locations are typically difficult to protect by painting. The interfacebetween steel beams and other metal elements such as steel decking may betreated similarly.

One advantage of Denso tape is that the amount of surface preparation required isminimal. All that is usually required is the removal of loose rust, dirt, paint etc. fromthe surfaces. The primers and fillers can then be applied.

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Guidance on the appropriate Denso Tape treatment and its correct applicationshould be sought from the manufacturer.

Caution:Corrosion protection systems such as Denso Tape wrapping and epoxy filling mayhide critical defects such as fatigue cracks. Such defects may be difficult to detectduring normal inspections and may result in collapse of the structure.Corrosion protection systems such as these should not be used on fatigue-criticalelements unless appropriate procedures to regularly check for and detect cracks areimplemented.

5.1.3 Procedure

Prepare for and apply Denso Tape, epoxy fillers etc. in accordance with themanufacturer's recommendations.

Where patch painting is to be used for corrosion arrest, refer to sub-procedure 5.3.

5.1.4 Materials

Refer to the manufacturers of Denso Tape systems and epoxy resins for advice onsuitable materials for each particular case.

5.1.5 Alternative details

None

5.2. Removing rivets and replacing with bolts (Sub-procedure)

5.2.1 Description of action

This sub-procedure covers the removal of existing rivets and replacement with highstrength friction grip bolts and also installation of new high strength bolts. Often thebolts also attach new steel elements.

5.2.2 Procedure:

5.2.2.1 Remove one head of the rivet:

To remove rivet heads, one of three methods are usually used:

cutting using oxy-fuel equipment;

grinding off all or part of the head; or

drilling through the centre of the rivet head.

Oxy-fuel cutting:

Because of the possibility of creating heat affected zones in tension regions ofmain members and adversely affecting their fatigue life, avoid using oxy-fuelcutting to remove the head except where it is adjacent to:

1. any steel that is to be removed and discarded as part of the repair process;

2. intermediate web stiffeners; or

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3. minor bracing members that are not subject to dynamic or cyclic loading.

Do not allow the oxy flame or molten steel to touch any other steel elementexcept those listed above.

In cases 2) and 3) above, where the steel adjacent to the rivet head is to remainin place, take care to avoid or minimise flame effects on that steel, to leave a neathole for installation of the bolts.

If the use of oxy-fuel cutting cannot be avoided in cases other than those above,take great care to avoid flame effects on the adjacent steel. Any flame affectedsteel around the hole must be completely removed by reaming prior to installingthe bolt.

Grinding:

If removing the head by grinding, it is only necessary to remove the portion of thehead outside the shank diameter.

Take care to avoid creating grooves and indentations in steel that is to remain inplace. If such indentations and grooves occur, remove them by grinding thesurface smooth after removing the rivet.

Where large numbers of rivets are to be removed, consideration should be givento procuring a grinding bit such as a broaching bit which, when positionedcentrally on the domed head will grind away material outside the shank diameter.

Drilling:

Rivet heads may be removed by drilling along the axis of the rivet with a drillingbit larger in diameter than the shank.

5.2.2.2 Remove the rivet

After the head of the rivet has been removed, force the remaining part out of thehole by punching or using hydraulic rams etc. The rivets are often not easilyremoved by punching because of deformation of the shaft in slightly misalignedholes.

Alternatively, remove the rivet head and shank and prepare the hole to acceptthe new bolt in one operation by drilling all the way through the rivet. The drill bitsize must be slightly larger than the rivet hole size and must be of a size to suitinstallation of a high strength bolt.

First drill a small hole through the rivet. Where the remainder of the rivet cannotbe removed by the above means, it is permissible to burn a hole through thecentre of the shank using oxy-fuel equipment to assist in the removal process.As stated above, extreme care is required to avoid any flame effects on thesurrounding steel. This operation is only to be carried out by experiencedoperators. Any flame-affected areas of steel must be completely removed byreaming the hole prior to installing the bolt.

Refer to Appendix D for further information on techniques and equipment for saferemoval of rivets using oxy-fuel and other equipment.

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5.2.2.3 Prepare the hole for the bolt:

Prepare the hole to accept the bolt by reaming out the hole to the requireddiameter, then removing burrs etc. at the edge of the hole and creating a smooth,level surface on both sides for bedding the washer and bolt head. Grinding, wirebrushing and scraping may be used.

The hole diameter after reaming must be no more than 2 mm larger than thediameter of the bolt to be installed unless a plate washer is to be installed inaccordance with detail A on Fig 5.2.1. In the latter case the hole diameter maybe up to 10 mm greater than the bolt diameter.

Use reaming to remove any areas of steel around the hole that have beenflame affected during the removal of the rivet.

The minimum and maximum edge distances and spacings for new bolt-holes inexisting or new steel are to comply with the requirements of the Australian BridgeDesign Code.

5.2.2.4 Install the bolt:

Install the replacement bolt in accordance with the following specification. Table5.2.1 specifies minimum replacement bolt sizes. The arrangement for oversizeholes is shown in Detail A of Fig 5.2.1.

Specification for New or Replacement Bolts

1. All bolts are to be high strength structural bolts of grade 8.8 to AS 1252,fully tensioned to AS 4100 as a friction joint. Tension is to be controlled byload indicating washers or turn of nut method.

2. Swage bolts installed in accordance with the manufacturer's instructions,may be used as an alternative.

3. All bolts, nuts and washers are to be galvanized.4. Swage bolts, pins and washers are to be galvanised and the steel surface

exposed after separation of the pintail is to be painted.5. Nominal maximum hole diameter to be the diameter of the fastener +2mm

unless plate washers, as illustrated in Detail A are used, unless otherwisespecified for swage bolts.

6. For each standard rivet size the minimum size of replacement bolt to giveequivalent shear capacity is given in Table 5.1. Larger bolts may be used.

7. For Huck BOM blind fasteners, sufficient room must be available on theblind side to accommodate the expanded head. Refer to Detail B.

Rivet size Bolt size

8.8 T/F

Huck Bolt

C50L

Huck-Fit

Grade 10.9

Huck

BOM

3/4” M20 3/4” Ø20mm 3/4”

7/8” M24 7/8” Ø22mm -

1” M27 1” Ø27mm -

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Table 5.1 –Minimum replacement bolt sizes

If Huck bolts are used, the HUCK-FIT fastening system is recommended as the pinsare available in standard metric sizes including non-preferred sizes (M20, M22,M24, M27 etc.). The HUCK-FIT system allows fit up and snug tightening of boltsprior to tensioning. Huck bolts are to be installed in accordance with themanufacturer’s instructions.

5.2.3 Alternative details

If there is only access to one side of plates to be bolted, use Huck BOM blindfasteners, installed in accordance with manufacturer’s instructions. Use galvanisedBOM fasteners. Make sure there is adequate room for the enlargement of the blindside head. Refer to detail B in Fig 5.1.

Note that Huck BOM fasteners are not friction grip connectors and may not besuitable for all situations. Bolt slip may occur to the limit of the hole clearance. Slipcan be minimised by drilling close tolerance holes (19 to 20mm for ¾” as shown in Fig 5.1.

A similar blind fastener for high strength friction grip applications is available fromHuck on special order. It is known as the USBB (Ultra Strength Blind Bolt). Usethese fasteners when blind friction grip connections are essential.

5.3. Patch painting (including surface preparation)(Sub-procedure)

5.3.1 Description of action

Patch painting is required in conjunction with steel repair as a corrosion protectionsystem for new and existing steel in the vicinity of the repair, and to restore auniform appearance to the bridge.

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Patch painting to arrest corrosion may be the only form of repair required.

This sub procedure only covers painting to small areas where hand and power toolpreparation is the only feasible method.

Large areas, where the cost of abrasive blast cleaning can be justified, should bepainted in accordance with ARTC’s standard practices.

5.3.2 Engineering discussion

Paint systems for patch painting should ideally have the following characteristics:

Formulated to provide good adhesion and protection to poorly prepared steelsurfaces (hand or power tool preparation).

Formulated to bond to sound existing paints of the types typically found onbridges.

High build, single coat systems to minimise total painting time (i.e. adequate film thickness applied in one coat). Available in a large range of colours to blend with colour of existing paint and

avoid the necessity for a colour matched top coat. Able to bond adequately to galvanised steel. Suitable for top coating where a top coat is required.

Leading paint manufacturers have paint systems with most of the abovecharacteristics. One system specifically developed for this application is a two partsurface tolerant epoxy mastic.

ALKYD systems are not suitable for application to galvanised surfaces because thelong term bond cannot be guaranteed. Where galvanised parts have been fitted aspart of the repair and the selected patch paint system is not suitable for galvanisedsurfaces, the following options exist:

1. Leave the galvanised surface unpainted. Painting is normally onlynecessary to achieve a uniform appearance with the rest of the steel.Or

2. Use different single coat systems for galvanised and ungalvanised surfaces.Systems for galvanised surfaces are readily available. Galvanised parts canbe painted prior to installation.Or

3. Apply the standard single coat patch paint to ungalvanised surfaces thenapply a suitable top coat to both galvanised and patch painted surfaces. Topcoat systems suitable for such situations are available.Or

4. Paint new steel parts instead of galvanising them. Use the patch paintsystem on site or, where parts can be prepainted, use the paint systemadopted for repainting of bridges. Abrasive blast cleaning is required for thelatter.

The minimum surface preparation for small areas is usually specified by paintmanufacturers as hand or power tool cleaning to AS 1627.7 or 1627.2 Class 2. TheAustralian Standard referred to provides a full description of the methods andequipment to be used and the quality of surface finish required.

For rough surfaces, such as the surface of site fillet welds, special preparation andapplication procedures are required. Unless precautions are taken, the paint

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thickness on sharp ridges will be considerably less than the minimum required andpremature breakdown of the paint system may occur.

5.3.3 Procedure

5.3.3.1 Prepare the surface

For normal steel surfaces

Prepare the surfaces for painting in accordance with therecommendations of the paint manufacturer for the paint system to beapplied. Hand or power tool cleaning to AS1627.7 or AS1627.2 Class 2 isthe minimum requirement.

For rough surfaces

Remove sharp ridges and deep narrow grooves or pits from the steelsurface by power grinding. Alternatively, for the surface of site fillet welds,fill the surface to a smooth even finish using epoxy resin fillers such asthose used for void filling described in 5.4.

Where the depth of the roughness is less than 0.5mm, an adequate anddurable paint system can be achieved without the above surface levellingby applying multiple coats of the paint. Each coat is to be no more thanthe maximum film thickness recommended by the manufacturer. Enoughcoats are to be applied so that the minimum required dry film thickness(typically 150 microns) is achieved at all sharp ridges.

For galvanised surfaces

Prepare the galvanised surface for painting in accordance with the paintmanufacturer’s recommendations. Coating manufacturers usually recommend degreasing and abrasion, acid etching or pretreatment withetch (wash) primers prior to painting. Light abrasive blast cleaning (brushblasting) is the most reliable means of achieving satisfactory coatingadhesion. However, where light abrasive blast cleaning is impractical dueto the small areas involved, power wire brushing/hard scouring withaluminium oxide impregnated nylon pads to remove the shiny patina onnew galvanised steelwork and the white soluble zinc salts on old(weathered) galvanised steelwork is preferred to acid etching orpretreatment with etch primer.

5.3.3.2 Apply the paint

Mix the paint components and apply in accordance with the manufacturer’s instructions. The paint should be applied immediately after surface preparation,preferably within 4 hours, and certainly on the same day. The minimum total dryfilm thickness of the system should not be less than 125 micrometres.

5.3.4 Repair materials

Paint systems suitable for patch painting are listed in Appendix A. They are typically2 part epoxy based, high build systems.

5.3.5 Alternative details

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None.

5.4. Filling voids (Sub-procedure)

5.4.1 Description of action

When new steel plates or sections are fitted to existing steel as part of repairprocedures, voids may be created, usually as a result of the existing steel beingheavily corroded or pitted. The voids may need to be filled with epoxy resin for oneor both of the following reasons.

1. To preclude the ingress of air and moisture which would lead to furthercorrosion, and/or

2. To provide a smooth, level surface on to which the new steel elements canbe fitted. Engineering discussion

5.4.2 Engineering discussion

Where the latter is the reason for void filling, the epoxy filler is often structural. Itmay be required to resist the compressive forces created by the tensioning of boltsor, in the case of bearing plates, transfer bearing forces.

The necessity for void filling depends on the severity of corrosion and uniformity andgeneral profile of the corroded surface (after preparation). If the surface is uniformlypitted so that the surface remains generally flat and steel attachments would notdistort when fixed by tensioned bolts, void filling is not necessary. The steel surfacewould still be able to transfer forces described above. (Sealing the steel to steelinterfaces, however, may be required–refer to sub-procedure 5.5.)

On the other hand, severely corroded surfaces that are uneven normally requirefilling prior to covering with new steel parts to prevent distortion of those parts.

Notwithstanding the above, it may be worthwhile applying epoxy fillers to any deeplycorroded surface prior to attaching new parts. As well as filling voids, the epoxy actslike a primer paint and also seals the interface between new and existing steel readyfor painting. The requirement for sealing interfaces prior to painting is discussed insub-procedure 5.5. The adhesive quality of epoxies may also be useful in somerepairs.

Two alternative procedures for applying filling epoxies are described below. In thefirst, the covering steel member is fitted before the epoxy has hardened and excessepoxy is squeezed out during bolt tightening. Squeezing out excess epoxy ensuresthe void is completely filled. In the second procedure, the epoxy is trowelled orscreeded smooth and flat and allowed to harden prior to fitting the steel member.

Select the procedure which best suits the repair being carried out. Considerparticularly the hardening time for the epoxy.

5.4.3 Procedure

5.4.3.1 Alternative 1 –New steel elements fitted before epoxy hardens

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1. Prepare the existing steel surface by abrasive blast cleaning to Class 2½ inaccordance with AS 1627.4. If abrasive blast cleaning is impractical dueto small areas involved power tool clean to Class 2 in accordance with AS1627.2.

2. Mix the epoxy according to the manufacturer’s directions and apply to the steel surface. Trowel and screed into position to the approximate surfacerequired. Ensure that there is a slight excess of epoxy that can besqueezed out when the steel part is fitted. Make sure there is anadequate escape path for excess epoxy.

3. While the epoxy is still plastic, position the new steel part and install thefixing bolts. Use the tightening of the bolts to bring the steel part into thecorrect position and squeeze out excess epoxy. Bolts may only be fullytensioned prior to curing if the

4. member would not distort and be forced out of position by such action. If indoubt about the effects of bolt tensioning, wait until the epoxy has cured

5. Clean away excess epoxy and make sure all steel to steel interfaces areeffectively sealed at the perimeters ready for painting. (Refer to sub-procedure 5.5 for sealing requirements).

6. Tension the bolts after the epoxy has cured.

5.4.3.2 Alternative 2 –New steel elements fitted after epoxy hardens

1. Prepare the existing steel surface by abrasive blast cleaning to Class 2½in accordance with AS 1627.4. If abrasive blast cleaning is impracticaldue to small areas involved power tool clean to Class 2 in accordancewith AS 1627.2.

2. Mix the epoxy according the manufacturer’s directions and apply to the steel surfaces. Screed the epoxy to the smooth, flat surface requiredusing a straight edge screed. If necessary to achieve a flat surface, applythe epoxy in two or more coats with each successive coat filling anyvalleys until the required flatness is achieved.

3. Clean away excess epoxy. Ensure that empty bolt holes are notobstructed by epoxy.

4. After the epoxy has cured, fit the steel part and fully tension any bolts.5. Seal any remaining gaps at interfaces in accordance with sub-procedure

5.4.4 Repair materials

Use high strength, two part epoxy fillers or adhesives. Epoxies should have highstrength and non-sag properties if they are to be applied to overhead or verticalsurfaces. Select an epoxy with a work time appropriate to the repair being carriedout. Refer to Appendix A for suggested products.

When application procedure 2 is to be used, choose an epoxy which is suitable forworking and screeding.

Seek advice from recognised manufacturers to select the best epoxy and applicationprocedure for the particular repair.

5.4.5 Alternative details

Where the thickness of epoxy filler to be applied is significant, a combination of bothprocedures described above may be used. Use procedure 2 to apply the bulk of thefiller, and leave the surface at or below that required, and approximately even. Thenuse procedure 1 to fill the remaining dips and valleys in the surface.

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5.5. Sealing interfaces (Sub-procedure)

5.5.1 Description of action

In repairing steel, gaps may occur at the interface between new and existing steel,often as a result of the existing steel being corroded. In these and similar situationsthe gaps are to be sealed with a single component polyurethane sealant prior topainting when they are greater than a specified width.

5.5.2 Engineering discussion

Paint manufacturers recommend against painting over large gaps.

While the applied paint may initially span these gaps, it may subsequently crack dueto drying shrinkage or it may not cure properly because of the excess film thickness.Gaps of width more than twice the maximum recommended film thickness or 0.5mmare to be sealed as described.

5.5.3 Procedure

1. Prior to fitting new steel elements, prepare existing steel surfaces byabrasive blast cleaning to Class 2½ in accordance with AS 1627.4. Ifabrasive blast cleaning is impractical due to small areas involved power toolclean to Class 2 in accordance with AS 1627.2.

2. Identify areas to be sealed. Interfaces where the gap exceeds 0.5mm ortwice the maximum recommended dry film thickness are to be sealed with asingle component polyurethane sealant. Sealing is required whether theconcealed steel surfaces are painted or bare steel.

3. Break inner seal at extrusion end of cartridge, affix nozzle, cut tip to suit jointsize, install in caulking gun and apply in accordance with the manufacturersinstructions.

5.5.4 Materials

Use a single component polyurethane sealant suitable for being painted over withsolvent-based paints. Refer to Appendix A for use of appropriate products.

5.5.5 Alternative details

Where voids between steel elements are to be filled (refer sub-procedure 5.4),extending the void filling epoxy to the edges of the steel will generally avoid thenecessity to seal interfaces as a separate operation. Refer to sub-procedure 5.4.

6. Repairing corroded flanges and webs of girders

6.1. Repairing flange corrosion in riveted girders

6.1.1 Description of defect

Loss of cross-sectional area of top or bottom flange plates in a riveted plate webgirder resulting from significant corrosion.

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This repair is also to be used where loss of cross-sectional area of flange angleshas occurred.

6.1.2 Description of repair

Fit a galvanised cover plate, sufficient in nett area to compensate for the lost cross-sectional area.

6.1.3 Engineering discussion

It will be necessary to carry out an engineering assessment to determine thenecessity for, and extent of, cover plating required. The assessment shoulddetermine the cover plate section size and the number and location of rivets that areto be replaced by bolts.

As a guide, up to 10% section loss is permissible before the repair is necessary. Thenett cross-sectional area of the cover plate should be at least twice the maximumarea of corrosion loss. The minimum plate thickness is to be 10 mm.

If a significant proportion of the section loss has also occurred in the flange angle(s),the engineering assessment should determine if the angle(s) is capable oftransferring shear force to the flanges. If not, the corrosion of the flange angle(s)should first be considered as a separate defect.

Consideration could be given to replacement of the continuous flange angle(s) byflange angle segments between web stiffeners. In this case the nett area of thecover plate must be sufficient to also compensate for the discontinuity of flangeangle(s).

In determining the extent of cover plating, the transfer of load (development ofstress) into the plate must be considered. Conservative guidelines for the number offasteners required to develop maximum permissible stress in the plate are detailedbelow.

1. The number of bolts in the cover plate must be sufficient to develop themaximum permissible strength in the cover plate

2. The number of bolts to achieve the above requirement is given in Table6.1, based on the nett area of the cover plate (Can) and the bolt size

Bolt size No. of boltsM20 5.4 x Can ÷ 1000M22 4.4 x Can ÷ 1000M24 3.7 x Can ÷ 1000M27 2.9 x Can ÷ 1000

Table 6.1 –Number of bolts in cover plate

Because only a few fasteners are removed at any one time, theoretically the girderremains at near full strength throughout the repair. Nearly all existing rivets can bereplaced by bolts if necessary. Bracing connected by flange rivets must remainadequately connected.

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To avoid unnecessary work however, only the minimum number of rivets, as shownby engineering assessment, should be replaced by bolts.

The maximum edge distance and fastener spacing given in sub-procedure 5.2should be observed so that the interface to the cover plate is tight and crevicecorrosion is avoided.

6.1.4 Sub-procedures required

Ref 5.2 Removing Rivets and Replacing with Bolts

Ref 5.3 Patch Painting (including surface preparation)

Ref 5.4 Filling Voids

Ref 5.5 Sealing Interfaces

6.1.5 Procedure outline

1. Remove heads of rivets that are to be replaced by bolts. Remove the underside heads for bottom flanges and the top side heads for top flanges. Fortop flange rivet removal, fit clamps to the under side to prevent rivets fallingout. Removal of rivets is to be in accordance with sub-procedure 5.2

2. Prepare the flange surface for cover plating by removing all loose rust anddirt and by grinding where necessary to create a smooth surface. Fill anydeep pitting (>1mm deep) or any area of unevenness in accordance withsub-procedure 5.4 to create a flat surface for seating the cover plate.

3. Position the pack plates and cover plate, holding them in place withclamps.

4. Progressively remove rivets to be replaced and fit and tension replacementbolts, all in accordance with sub-procedure 5.2. No more than 10% ofrivets, evenly distributed along member, are to be removed at any onetime.

5. Seal open interfaces to new steel where required in accordance with sub-procedure 5.5. Fill exposed rivet head holes on the top flange inaccordance with sub-procedure 5.4 to prevent collection of water.

6. Prepare for and paint new steelwork and areas of existing steelwork to theextent directed, in accordance with sub-procedure 5.3.

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6.1.6 Action to avoid or minimise recurrence

1. Routine maintenance to remove built-up dirt and debris on the uppersurfaces.

2. Routine maintenance to the paint system.

6.1.7 Alternative details

None

6.1.8 Special considerations and effects of repair.

The engineering assessment may determine that speed restrictions or a trackpossession is required while this repair is being carried out.

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6.1.9 Follow-up inspections and testing

Programmed inspections only.

Pay particular attention to new steel to steel interfaces to detect early signsof paint system breakdown and steel corrosion.

6.1.10 Drawings List

Figure 6.1

6.2. Repairing flange corrosion in rolled or welded girders

6.2.1 Description of defect

Loss of cross-sectional area of top or bottom flange plates in a welded or rolledgirder resulting from significant corrosion.

6.2.2 Description of repair

Fit a galvanised cover plate sufficient in nett area to compensate for the lost cross-sectional area.

6.2.3 Engineering discussion

It is usually necessary to carry out an engineering assessment to determine thenecessity for and extent of cover plating required. The assessment shoulddetermine the cover plate section size and the number, size and location ofconnection bolts required.

As a guide, up to 10% section loss is permissible before the repair is necessary.The nett cross-sectional area of the cover plate should be at least twice themaximum area of corrosion loss. The minimum plate thickness is to be 10 mm. Thenett area of cover plate must also compensate for the existing flange area lost indrilled holes.

In determining the extent of cover plating, the transfer of load (development ofstress) into the plate must be considered.

Conservative guidelines for the number of fasteners required to develop maximumpermissible stress in the plate are detailed below.

The number of bolts in the cover plate must be sufficient to develop the maximumpermissible strength in the cover plate

The number of bolts to achieve the above requirement is given in Table 6.2, basedon the nett area of the cover plate (Can) and the bolt size.

Bolt size No. of boltsM20 5.4 x Can ÷ 1000M22 4.4 x Can ÷ 1000M24 3.7 x Can ÷ 1000M27 2.9 x Can ÷ 1000

Table 6.2 –Number of bolts in cover plate

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The strength of the girder is reduced during the repair because of the holes drilled inflange. Appropriate load and/or speed restrictions must be applied.

The maximum edge distance and fastener spacing given in sub-procedure 5.2should be observed so that the interface to the cover plate is tight and crevicecorrosion is minimised.

6.2.4 Sub-procedures required

Ref 5.2 Removing Rivets and Replacing with Bolts

Ref 5.3 Patch Painting (including surface preparation)

Ref 5.4 Filling Voids

Ref 5.5 Sealing Interfaces

6.2.5 Procedure outline

1. Mark and drill holes in the flange to suit the cover plate

2. Prepare the flange surface for cover plating by removing all loose rust anddirt and by grinding where necessary to create a smooth surface fill anydeep pitting (>1mm deep) or any area of unevenness in accordance withsub-procedure 5.4 to create a flat surface for seating the cover plate.

3. Position the cover plate, holding it in place with clamps.

4. Fit and tension all bolts.

5. Seal open interfaces to new steel where required in accordance with sub-procedure 5.5.

6. Prepare for and paint new steelwork and areas of existing steelwork to theextent directed in accorance with sub-procedure 5.3.

6.2.6 Alternative details

6.2.7 Action to avoid or minimise recurrence

None.

Routine maintenance to remove built-up dirt and debris on the upper surfaces.

Routine maintenance to the paint system.

6.2.8 Special considerations and effects of repair

The engineering assessment may determine that speed restrictions or a trackpossession is required while this repair is being carried out.

6.2.9 Follow-up Inspections and testing

Programmed inspections only.

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Pay particular attention to new steel to steel interfaces to detect early signs of paintsystem breakdown and steel corrosion.

6.2.10 Drawings

Figure 6.2.

6.3. Repairing web corrosion near bottom flange angles in riveted girders

6.3.1 Description of defect

Severe Corrosion of the web of a riveted girder at the junction of the upper toe of thebottom flange angle(s). Loss of web section in plan view results.

6.3.2 Description of repair

Fit galvanised cover plates over the region of corrosion loss. The cover plates are tobe in discrete lengths between web stiffeners.

6.3.3 Engineering discussion

It is recommended in most cases that an engineering assessment be carried out todetermine the necessity of repair and the locations where cover plate segments arerequired.

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In the absence of engineering assessment, the following guidelines should beapplied: Cover plate the segment of web between stiffeners where the average lossof web area in the panel in plan view exceeds 15%.

In the engineering assessment, the necessity for a cover plate should be based onthe ability of the remaining web area (plan view) to transfer the shear stresses to theflange.

This repair may not be satisfactory at the girder bearing location where stressesadditional to shear stresses occur.

It should be recognised that the shear transfer stresses are often low, particularly inthe middle half of the span, so considerable section loss may be tolerable.Corrosion arrest may be all that is required. Irrespective of shear transfer stresslevels, the web panel should be repaired where section loss exceeds 40%.

Alternative repair details involving site welded cover plates are not normallyacceptable because of the significant reduction in fatigue life that results fromwelding fitments in this tensile zone.

If a detailed engineering assessment is not carried out the cover plate shouldincorporate all rivets through the vertical leg of the flange angle. The upper part ofthe cover plate should be attached by bolts of the same number and size as thelower part.

An engineering assessment may determine that a reduced number of bolts isadequate for a particular web panel.

6.3.4 Sub-procedures required

Ref 5.1 Arresting Corrosion

Ref 5.2 Removing Rivets and Replacing with Bolts

Ref 5.3 Patch Painting (including surface preparation)

Ref 5.4 Filling Voids

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6.3.5 Procedure outline

1. Remove all loose rust from the surface to be plated by mechanical wirebrushing and scraping. Scrape or grind smooth the vertical face of flangeangles.

‘Working on only one panel of web at a time:

2. Drill holes in the web above flange angle to match the holes in theprefabricated, galvanised cover plate and pack plate.

3. Remove the rivets through vertical legs of angles in accordance with Sub-procedure 5.2.

4. Position the pack plate and fill the void between the pack and the flangeangle in accordance with sub-procedure 5.4.

5. Fit the cover plate and install and tension all bolts. Repeat steps 2, 3, 4 and5 for each web panel requiring plating, then

6. Prepare for and patch paint new steelwork and areas of existing steelworkto the extent directed, including the region of corrosion on the unplatedside. Patch painting to be in accordance with sub-procedure 5.3.

Caution:

Rivets must NOT be removed from more than one panel of web at any one time.

6.3.6 Alternative details

Cover plates may be fitted to both sides of web to improve appearance by coveringthe area of web corrosion.

6.3.7 Action to avoid or minimise recurrence

Routine maintenance of paint system particularly at crevices and steel to steelinterfaces.

The repair detail presents a similar situation to the original corrosion prone details soproper maintenance of paint system is essential to avoid recurrence of the defect.

6.3.8 Special considerations and effects of repair

The engineering assessment may determine that speed restrictions or a trackpossession is required while this repair is being carried out.

6.3.9 Follow-up inspections and testing

Programmed inspections only.

Pay particular attention to new steel to steel interfaces to detect early signs of paintsystem breakdown and steel corrosion.

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6.3.10 Drawings

Figure 6.3

6.4. Repairing webs with localised corrosion

6.4.1 Description of defect

Localised severe corrosion of a web leading to significant loss of web section in planview. Typically this defect occurs where concrete ballast troughs have been indirect contact with the girder web.

6.4.2 Description of repair

Fit galvanised cover plates over the regions of web where the section loss hasoccurred. The cover plates are to be in discrete lengths between web stiffeners.

6.4.3 Engineering discussion

It is recommended that an engineering assessment be carried out to determine theeffect of the section loss on the girder shear capacity and hence the necessity ofrepair and the location, size and bolt arrangement of cover plates.

In the absence of an engineering assessment, the following guidelines may beapplied: Segments of web between stiffeners are to be cover plated where the lossof area in sectional view exceeds 10% of the total web area or where the loss ofarea in plan view exceeds 15%. Guidelines for the size and spacing of attachmentbolts are given in Figure 6.4

It should be recognised that, where the web thickness is constant for the girder,there is often an excess of shear capacity, particularly near mid span. Aconsiderable loss of section may be tolerable at these locations before the repair isrequired. The assessment may show that only corrosion arrest is required in somepanels where section loss exceeds the above guideline figures.

The engineering check on the reduced shear capacity of the web must, of course,consider web buckling as well as shear stresses.

Alternative repair details involving welded cover plates may be permissible if testingindicates that the steel is weldable and welding does not reduce the fatigue lifeunacceptably.

Corrosion loss, localised near the mid-height of the girder in panels near mid-span,may be repairable by using welded cover plates, as tensile stresses in these areasare low. Do not weld to web stiffeners.

It is important to note that significant principal tensile stresses occur at mid-height ofgirders near the span ends as a result of shear forces. Welded cover plates are notnormally permitted here because of the adverse effect on fatigue life.

6.4.4 Sub-procedures required

Ref 5.2 Removing Rivets and Replacing with Bolts

Ref 5.3 Patch Painting (including surface preparation)

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Ref 5.4 Filling Voids

Ref 5.5 Sealing Interfaces

6.4.5 Procedure outline

1. Cut back reinforced concrete etc. that is causing corrosion as directed.

2. Remove all rust, dirt, adhering concrete, old paint etc. from the area to beplated by mechanical wire brushing and scraping.

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3. Mark and drill bolt holes in the web to match the holes in prefabricated,galvanised cover plates.

4. Fill voids and surface pitting with epoxy resin filler over area of web to becovered in accordance with sub-procedure 5.4

5. Position cover plates and fit and tension bolts. Seal with epoxy any openinterfaces around the perimeter of the cover plates in accordance with sub-procedure 5.5.

6. Prepare for and patch paint new steelwork and areas of existing steelworkto the extent directed.

6.4.6 Alternative details

None.

6.4.7 Action to avoid or minimise recurrence

Remove concrete cast directly against or in close proximity to web. Reconstructaccessways etc. to approved details, e.g. using gridmesh.

Routine maintenance of paint system, particularly at crevices and steel to steelinterfaces.

6.4.8 Special considerations and effects of repair

None

6.4.9 Follow-up inspections and testing

Programmed inspections only.

Pay particular attention to new steel to steel interfaces to detect early signs of paintsystem breakdown and steel corrosion.

6.4.10 Drawings

Figure 6.46.5. Repairing corroded bottom flanges of jack arch bridges

6.5.1 Description of defect

Severe corrosion of the bottom flange of jack arch bridge girders resulting in asignificant loss of cross-sectional area.

6.5.2 Description of repair

Fit a galvanised cover plate to the bottom flange sufficient in cross-sectional area tocompensate for the loss of cross-sectional area. If the existing steel is weldable,connect the cover plate by welding (Case B). Otherwise use Huck BOM blindfasteners. (Case A)

6.5.3 Engineering discussion

This repair is only effective in restoring full strength if the remainder of the Ι-sectionis in good condition. It is difficult to determine the condition of the girders in a jack

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arch bridge as only the underside of the bottom flange can be readily inspected forloss of section.

An engineering assessment should be carried out to determine:

the necessity of the repair;

if the repair is likely to be effective in restoring full strength;

if the steel is weldable;

the size and extent of the cover plate and, if bolted connections are to beused, the arrangement of connection bolts.

Use bolted connections if the steel is not weldable or the existing flange edge isseverely feathered, precluding welding. Feathered edge to be ground to provideminimum 5mm thickness.

As a guide, the repair should be carried out if loss of bottom flange cross sectionexceeds 15%. The nett area of the cover plate should be at least twice themaximum area of cross-sectional loss, plus the area removed by drilling for fixingbolts. The minimum plate thickness is to be 10mm and the width selected to suit thebolt gauge and edge distance or weld details. Extend the cover plate as close to thebearings as possible (within span/10) so the termination weld is in a region of lowstress.

An engineering assessment may show that other details are acceptable.

Where bolted fixings are used, the spacing and edge distances must comply withthe requirements of the Australian Bridge Design Code. Refer to sub-procedure 5.2.

6.5.4 Sub-procedures required

Ref 5.2 Removing Rivets and Replacing with Bolts

Ref 5.3 Patch Painting (including surface preparation)

Ref 5.4 Filling Voids

Ref 5.5 Sealing Interfaces

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6.5.5 Procedure outline

6.5.5.1 Case A –Bolted Cover Plate

1. Prepare the flange surface for cover plating by removing all loose rust anddirt and by grinding where necessary to create a smooth surface. Fill anydeep pitting (>1mm deep) or any area of uneveness in accordance withsub-procedure 5.4 to create a flat surface for seating the cover plate.

2. Mark and drill holes in the bottom flange to suit the cover plate. For eachhole, excavate a small pocket in the concrete or masonry on the blind sideto accommodate the expanded blind side head of the Huck BOM fastener.A suitable grinding bit on power drill can be used. Refer to Figure 5.1.

3. Fit the galvanised cover plate and attach with Huck BOM blind fasteners allin accordance with sub-procedure 5.2.

4. Seal open interfaces to the cover plate where required in accordance withsub-procedure 5.5.

5. Prepare for and paint new steelwork and areas of existing steelwork to theextent directed, in accordance with sub-procedure 5.3.

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6.5.5.2 Case B –Welded Cover Plate

1. Prepare the flange surface for cover plating by removing all loose rust anddirt and by grinding where necessary to create a smooth surface. Fill anydeep pitting (> 1mm deep) or any area of uneveness in accordance withsub-procedure 5.4 to create a flat surface for seating the cover plate.

2. Fit the cover plate and hold in place. Weld longitudinally in accordance withthe details on Figure 6.5. Note the alternative welding arrangementsdetailed –one permitting overhand welding but requiring good access, theother requiring down hand welding, but with restricted access. Epoxy sealtransverse joint, no weld.

3. Prepare the surface of the fillet weld for painting in accordance with sub-procedure 5.3.

4. Prepare for and paint new steelwork and areas of existing steelwork to theextent directed, in accordance with sub-procedure 5.3.

6.5.6 Alternative details

Bolted and welded cover plate alternatives are detailed.

For welded cover plate, alternative arrangements for the welding are detailed.

6.5.7 Action to avoid or minimise recurrence

Routine maintenance.

Check for debris build up and corrosion of cover plate overhangs.

Special consideration and effects of repair

Traffic restrictions may be required if drilling holes removes a significant amount ofcross-sectional area.

6.5.8 Follow-up inspections and testing

None

6.5.9 Drawings list

Figure 6.5a and Figure 6.5b.

7. Repairing stiffeners, bracing connections and bearings

7.1. Relief of corrosion site at the base of intermediate web stiffeners

7.1.1 Description of defect

Severe corrosion at the base of riveted angle type intermediate web stiffeners and inthe adjacent bottom flange where

the local corrosion of the web stiffener is not structurally significant, but

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corrosion and loss of section of the flange is significant or potentiallysignificant. Corrosion of bearing stiffeners and stiffeners at connections ofcross-girders and bracing are not covered by this procedure.

7.1.2 Description of repair

The repair involves removal of the unnecessary portion of stiffener to result in adetail that can be readily cleaned, painted and maintained to prevent furthercorrosion but is structurally satisfactory. Intermediate web stiffeners may beterminated 50 to 100 mm from the bottom flange and still perform their requiredfunction.

7.1.3 Engineering discussion

The removal of the lower portion of true intermediate web stiffeners is normallystructurally acceptable. It is often not acceptable for stiffeners that form part of theconnection or force transfer system of cross-girders or bracing.

If the stiffener is to be cut using oxy-fuel equipment, extreme care is required toensure that there are no flame effects on the web, flange or flange angles. Evensmall flame strikes can create fatigue initiation sites. The recommended locationsfor cutting stiffeners have been chosen to minimise the chances of oxy flame effectson the girder.

Where necessary, an angle grinder should be used to cut the segment of stiffenerclosest to the girder.

If corrosion at the base of the stiffener has already resulted in significant corrosionloss in the flange or flange angle, repair the flange using repair procedure 6.1 ifnecessary and appropriate.

7.1.4 Sub-procedures required

Ref 5.1 Arresting corrosion

Ref 5.2 Removing rivets and replacing with bolts

Ref 5.3 Patch painting (including surface preparation)

7.1.5 Procedure outline

1. Remove any rivets securing the lower portion of the web stiffener that is tobe removed in accordance with sub-procedure 5.2.

2. Cut off the lower portion of the stiffener to the extent shown on Figure 7.1aor Figure 7.1b by flame cutting and/or with an angle grinder. Severalpossible arrangements of web stiffeners are shown on the drawing. Theappropriate location for the cut is shown in each case.

To avoid accidental creation of heat affected zones (fatigue sites) in theadjacent web and flange, do not use flame cutting to remove portions ofintermediate web stiffeners in direct contact with the web or flange. Use anangle grinder to cut these portions. Take care to avoid grinding a grooveinto the web or flange.

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3. Dress any flame cut edge to the stiffener by grinding smooth and fit andtension bolts to any holes formerly occupied by rivets.

4. Prepare for and patch paint the exposed steel of the web stiffener and thelocal area of bottom flange and flange angle now exposed in accordancewith sub-procedure 5.3.

7.1.6 Alternative details

None.

7.1.7 Action to avoid or minimise recurrence

Not applicable.

7.1.8 Special considerations and effects of repair

The removal of the lower portion of web stiffeners as detailed is only permissible intrue intermediate web stiffeners performing no other structural functions. Somestiffeners also form part of the connection of cross-girders or bracing. Similarly, theprocedure must not be applied to bearing stiffeners.

7.1.9 Follow-up inspection and testing

Programmed inspections only.

7.1.10 Drawing list

Figure 7.1a and Figure 7.1b.

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7.2. Repairing intermediate and bearing web stiffeners with localised corrosion

7.2.1 Description of defect

Severe corrosion of web stiffeners over a limited area leading to loss of cross-sectional area in plan view. The repair procedure is intended to cover riveted anglestiffeners but may be adapted to other situations.

7.2.2 Description of repair

Two cases are covered by this repair procedure:

Case A –Corrosion away from end of stiffeners

If the region of severe corrosion loss is away from both ends of the stiffener, therepair procedure involves lap splicing a new segment of stiffener angle, connectedto the existing stiffener above and below by bolting. A sufficient length ofuncorroded stiffener must be available above and below to effect the boltedconnection.

Case B –Corrosion near end of intermediate stiffener

If the region of severe corrosion loss is at one end of the stiffener only, the repairprocedure involves removing the corroded segment of stiffener, fitting a replacementsegment and splicing it to the existing stiffener in a similar manner to Case A. Asufficient length of uncorroded stiffener must be available at one end to effect thebolted connection.

7.2.3 Engineering discussion

Corrosion may occur at the bottom end of web stiffeners because of entrapment ofwater by the detail. It may occur away from the ends where concrete or timberelements are in close contact with the steel (crevice corrosion). When repairs arecarried out, the cause of the corrosion should be eliminated if possible.

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The repair procedure addresses corrosion of stiffeners over a localised area. If theweb stiffener is severely corroded over its entire length, it can be completelyreplaced as described in Section 11.1

If the corrosion is limited to a small non-essential part of the stiffener at the base, theprocedure described in 7.1 may be appropriate.

Isolated Web Stiffeners:

Isolated web stiffeners (ie. Those not associated with the connection of bracing orcross-girders etc.) can sustain substantial loss of cross-section before repair isrequired. As a guide, the repair should be carried out if the loss of section exceeds30% (evenly spread). If the loss is localised to the outer edge, the repair should becarried out if the section loss exceeds 15%.

An engineering assessment may be carried out to determine if greater sectionlosses are acceptable without repair.

If corrosion loss is acceptable, sub-procedure 5.1 for arresting corrosion should becarried out and the cause of corrosion should be eliminated if possible.

Web Stiffeners at Bracing Connections:

Web stiffeners, located at the connections of bracing members, are often an integralpart of the system of transferring bracing forces. In such cases the amount ofsection loss that can be accepted is less. Unless otherwise shown by anengineering assessment, the repair should be carried out if the section loss exceeds10%.

The repair details require an adequate length of existing stiffener to remain to effectthe bolted connection. These remaining sections must have no more than 10% lossof section. Guidelines for the number of bolts to connect the stiffener are given inTable 7.1 below.

Size of outstand leg ofstiffener

No. of connectingbolts

Size of connectingbolts

Up to 75 x 10 2 M20Up to 100 x 10 3 M20Up to 125 x 10 3 M24Up to 150 x 6 4 M24

Table 7.1 –Bolt details for stiffener repair

In Case A, the segment of stiffener with excessive corrosion may remain in placeprovided the corrosion is arrested. Feathered edges to be ground to 5mm minimumthickness.

Connection of the replacement stiffener piece by bolting rather than welding isproposed as the standard repair. Steels of stiffeners are often not weldable and,even if weldable, the welding process may create fatigue initiation sites in the web atthe new butt welds in the stiffener angle.

Where it can be shown by engineering assessment that the effects on the web ofwelding the stiffener do not result in an inadequate fatigue life, the welded splicedetail shown in Figure 7.2b may be adopted. Where there is a pack plate between

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the stiffener and the web, the web is adequately protected and the welded splicedetail may be adopted. The stiffener steel must be weldable, as determined byappropriate tests.

Note that the mid-height region of webs is not an area of low tensile stress if there issignificant shear stress at the section (resulting in principal tensile stress, e.g. nearbearings).

7.2.4 Sub-procedures required

Ref 5.1 Arresting Corrosion

Ref 5.2 Removing Rivets and Replacing with Bolts

Ref 5.3 Patch Painting (including surface preparation)

Ref 5.4 Filling Voids

Ref 5.5 Sealing Interfaces

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7.2.5 Procedure outline

Case A - Corrosion away from end of stiffener1. Mark and drill holes in the existing stiffener and web to suit the

prefabricated splicing angle. Refer to Figure 7.2a.

2. If directed, cut away the severely corroded portion of stiffener by flamecutting and by using an angle grinder. Avoid flame effects and grinding ofgrooves in the web plate. Dress any flame cut edges.

3. Clean existing steelwork where new steel is to abut. Fill pitting anddepressions in the surface in accordance with sub-procedure 5.4 so thereis no void between the web and the new stiffener segment.

4. Bolt in place the new galvanised stiffener segment, installing new bolts inaccordance with the appropriate part of sub-procedure 5.2.

5. Seal any gaps at the interface between new and existing steel inaccordance with sub-procedure 5.5.

6. Prepare for and patch paint new and existing steel to the extent directed inaccordance with sub-procedure 5.3.

Case B - Corrosion near end of stiffener

1. Remove rivets connecting the part of web stiffener to be removed inaccordance with sub-procedure 5.2.

2. Cut away the corroded portion of stiffener by flame cutting and by using anangle grinder. Avoid flame effects and grinding grooves in the web plate.Dress any flame cut edges.

3. Clean existing steelwork where new steel is to abut. Fill pitting anddepressions in the surface in accordance with sub-procedure 5.4 so thereis no void between the web and the new stiffener segment.

4. Fit the prefabricated, galvanised replacement segment of stiffener inaccordance with the details in Figure 7.2b and sub-procedure 5.2. Fit onlyfor "bracing connection" stiffeners, otherwise just remove.

5. Mark and drill bolt holes in the web to match the holes in the splicing angle.

6. Fit the prefabricated galvanised splicing angle in accordance with details onthe drawing and sub-procedure 5.2.

7. Seal any gaps at the interface between new and existing steel inaccordance with sub-procedure 5.5.

8. Prepare for and patch paint new and existing steel to the extent directed inaccordance with sub-procedure 5.3.

7.2.6 Alternative details

None.

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7.2.7 Action to avoid or minimise recurrence

Corrosion at the base of stiffeners can be addressed by stopping the new stiffenersegment above the bottom flange (if structurally acceptable) (Case B only). Referalso to sub-procedure 5.1 Arresting Corrosion.

7.2.8 Special considerations and effects of repair

None.

7.2.9 Follow-up inspection and testing

Programmed inspections only.

7.2.10 Drawing list

Figure. 7.2a and Figure 7.2b.

7.3. Repairing bearing web stiffeners with localised corrosion at base of outstandleg of stiffener

7.3.1 Description of defect

Severe corrosion and perforation to the outstand leg of riveted angle bearingstiffeners at base, where the remaining leg is in good condition.

7.3.2 Description of repair

The repair involves the removal of the severely corroded and perforated portion ofthe outstand leg of bearing stiffener and bolting a new plate to the outstand leg. Thenew plate must bear hard on bottom flange.

7.3.3 Engineering discussion

See 7.1.3.

7.3.4 Procedure outline

1. Cut away the corroded portion of outstand leg of stiffener by flame cuttingand by using an angle grinder. Avoid flame effects in the remaining leg ofstiffener. Dress any flame cut edges.

2. Clamp new plate with holes drilled to outstand leg. New plate must bearhard on bottom flange.

3. Drill existing stiffener and grind smooth all burrs.

4. Bolt new plate to existing stiffener.

5. Prepare for and patch paint new and existing steelwork.

7.3.5 Sub-procedure required

Ref 5.1 Arresting corrosion.

Ref 5.2.2.1 Oxy-fuel cutting.

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Ref 5.2.2.3 Preparing the hole for the bolt.

Ref 5.2.2.4 Install the bolt

Ref 5.3 Patch painting.

7.4. Relief of corrosion site at the base of splayed angle bearing end stiffeners

7.4.1 Description of defect

Severe corrosion or conditions conducive to corrosion at the base of a splayedangle bearing stiffener in riveted girders. Refer to Figure 7.4.

7.4.2 Description of repair

The "repair" involves a modification to the stiffener so that the area can be readilycleaned, painted and maintained to prevent further corrosion.

The modification is to remove a triangular section of the splayed segment of thebearing stiffener.

7.4.3 Engineering discussion

While the removal of the section of stiffener theoretically reduces the girder'sbearing capacity, the reduction is usually only marginal. However, engineering inputshould be sought before undertaking this repair. Note that the splayed section ofstiffener is usually connected by only one rivet. This gives an indication of the smallupper limit to the compression load in the stiffener.

The splayed angle bearing stiffeners are significantly less effective than end bearingtype stiffeners used in modern practice. If the bearing detail is performing poorlyunder live load (eg excessive flexing of bearing or bed plates etc.) thenconsideration should be given to replacing the splayed angle bearing stiffener withan end bearing type stiffener.

7.4.4 Sub-procedures required

Ref 5.3 Patch Painting (including surface preparation)

7.4.5 Procedure outline

1. Remove the section of stiffener as illustrated in Figure 7.4 by oxy-fuelcutting. Avoid or minimise flame effects on the steel of the girder section.

2. Dress the flame cut steel edges by grinding. Clean the area at the base ofthe stiffener of dirt and debris by power wire brushing, grinding etc.

3. Prepare for and patch paint the area in accordance with sub-procedure 5.3.

7.4.6 Alternative details

None

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7.4.7 Action to avoid or minimise recurrence

Corrosion at the base of stiffeners can be addressed by: Applying epoxy filler to the area to produce a contour that will readily drain

water away, or

Protecting areas vulnerable to corrosion with denso tape.

Refer to sub-procedure 5.1 - Arresting Corrosion.

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7.4.8 Special considerations and effects of repair

None.

7.4.9 Follow-up inspection and testing

Programmed inspections only.

Pay particular attention to maintenance of the paint system in the vicinity of thebearing.

7.4.10 Drawing list

Figure 7.47.5. Repairing corrosion at bottom flange bracing connection

7.5.1 Description of defect

Severe corrosion in riveted girders at the intersection of bracing, web stiffeners andthe bottom flange leading to significant loss of section in one or more of thecomponents.

7.5.2 Description of repair

The repair involves a replacement of severely corroded elements and possiblyadjustment of the detail, in a structurally acceptable manner, to avoid recurrence ofthe defect.

The repair procedure in 7.2 may be appropriate for the repair of web stiffeners.

Bracing members, damaged by corrosion, can be replaced in accordance with repairprocedure 11.1.

Where significant corrosion of the bottom flange has occurred, the repair procedurein 6.1 may be required.

Where the loss of section due to corrosion is less than that at which repair isrequired, sub-procedure 5.1 for arresting corrosion may be appropriate.

7.5.3 Engineering discussion

At the location under consideration, all the elements - the bottom flange, the webstiffeners and web, the braces and connection gusset

may be active parts of the bracing system.

It should be noted that in a sway bracing system, a bending moment will be appliedto the web stiffeners if the intersection of the centroids of the horizontal and diagonalbraces is not on the web centreline.

As a consequence, changes to the details to avoid further corrosion should not bemade in conjunction with the repair without an engineering assessment to determineif the resulting detail will be structurally satisfactory.

The standard repair procedure involves reinstatement of the detail, arrest ofcorrosion and protection against corrosion by an appropriate means.

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To assess the necessity for component repair or replacement, the followingguideline should be used: Repair or replace a component if the section loss,uniformly spread, exceeds 10%.

Notwithstanding the need for an engineering assessment, details of a possiblemodification of a typical connection are shown in Figure 7.5. The modification to thedetail involves cutting back of the horizontal leg of the brace angle to eliminate thehorizontal interface with the flange. If no rivets are removed by this modification it islikely to be structurally acceptable. If the degree of corrosion requires, the webstiffener is to be repaired in accordance with procedure 7.2 and the gusset platereplaced in accordance with procedure 11.1.

If the engineering assessment for the particular case indicates that the proposedmodification is not structurally satisfactory, consideration should be given tocompensating for the cut away leg of the brace angle by increasing the size andthickness or steel grade of the gusset plate and the number of connecting bolts.

Warning:

Bracing should be removed at only one location at a time and temporary bracing tocompensate must be installed if suitable load restrictions are not placed on the structure.

7.5.4 Sub-procedures required

Ref 5.1 Arresting Corrosion

Ref 5.2 Removing Rivets and Replacing with Bolts

Ref 5.3 Patch Painting (including surface preparation)

Ref 5.4 Filling Voids

Ref 5.5 Sealing Interfaces

7.5.5 Procedure outline

1. Install temporary braces as required to compensate for the braces that are to bedisconnected.

2. Remove rivets as necessary and remove the gusset plate.

3. If structurally acceptable, modify members as detailed by flame cutting or withan angle grinder. Avoid flame effects and grinding grooves on the flange andweb of main girder. Completely remove the brace if necessary to avoid theseeffects.

Dress any flame cut edges by grinding.

4. Repair the web stiffener if required in accordance with procedure 7.2.

5. Clean all steel surfaces of loose rust and paint by scraping and power wirebrushing.

6. Reassemble the connection with a new prefabricated galvanised gusset plate ifrequired. In the process fill voids, including surface pitting, as required by the

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detail in accordance with sub-procedure 5.4. Install new bolts in accordancewith sub-procedure 5.2.

7. ‘Prepare for and patch paint new and existing steel to the extent directed inaccordance with sub-procedure 5.3.

7.5.6 Alternative details

Consider complete replacement of connected bracing members.

7.5.7 Action to avoid or minimise recurrence

Included in procedure

7.5.8 Special considerations and effects of repair

As stated in 7.4.3, 7.5.3, 7.6.3, modification to the detail should only be made if anengineering assessment shows that it is structurally satisfactory.

7.5.9 Follow-up inspection and testing

Programmed inspections only.

7.5.10 Drawing list

Figure 7.5.

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7.6. Replacing bearing plates(See 22.4 for bearing pad replacement)

7.6.1 Description of defect

Severe corrosion of bearing plates and attachment bolts in riveted girder bridges.

7.6.2 Description of repair

The method of repair is to replace the bearing plate with a new galvanisedequivalent. The repair procedure describes methods of installing the new bearingplate with a minimum lift of the girder.

7.6.3 Engineering discussion

Weather conditions, in particular, buckling of track in hot weather must beconsidered before disturbing the bridge.

A severely corroded bearing plate should be replaced.

It may be prudent to replace a severely corroded bearing plate, even if it appears tofunction properly, to ensure the ongoing performance of the bridge.

Girder attachment bolts should be replaced if they are corroded to the extent thatthey are unable to restrain the girder against upward movement and/or if theyprevent longitudinal movement at the expansion end.

Restore the capacity of the girder to move longitudinally at the expansion end ifsevere corrosion and obstructions have removed this capacity.

If the repair is to be carried out with the bridge open to traffic, temporary support tothe girder including jacks, brackets, struts etc. are to be designed or selected to suitthe load that will be applied.

Where screws in tapped holes are used to attach the bearing plate, fabricate theplate from steel of grade 350 or higher. The screws then can be sufficientlytensioned.

7.6.4 Sub-procedures required

Ref 5.2 Removing Rivets and Replacing with Bolts

Ref 5.3 Patch Painting (including surface preparation)

Ref 5.4 Filling Voids

Ref 5.5 Sealing Interfaces

7.6.5 Procedure outline

1. Remove existing attachment bolts between girder and bed plate. Ifnecessary drill out the bolt shank to a larger diameter and tap the hole in thebed plate to suit the new attachment bolt. Alternative attachmentarrangement 2 or 3 shown in Figure 7.6b is to be adopted, drill and tap newholes in the bed plate to suit.

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2. Raise the girder(s) by jacking the minimum amount required to enablecompletion of the replacement operation. Raise all girders at one end,simultaneously if necessary, to avoid overstressing cross-connectingmembers. Lock jacks or pack under the girders to prevent accidentaldropping of the girders. If the bridge is to remain open to traffic, restrain thegirders longitudinally by blocking against the abutments, unless they aresuitably restrained at the remote end bearings.

3. Remove rivets connecting the bearing plates in accordance with sub-procedure 5.2 and remove the bearing plate.

4. Clean the bed plate and underside of the girder flange to remove loose rust,dirt etc. Use wire brushing if possible. Prepare the existing holes for newbolts by reaming, dressing etc. as required by sub-procedure 5.2.

5. If the underside of the flange is severely corroded, pitted or uneven, apply aneven coat of epoxy filler to the underside of the flange over the bearing platecontact area. Apply sufficient epoxy to fill any pitting voids on the undersideof the flange. Refer to sub-procedure 5.4 - Filling Voids.

Preferred Option

6. a) Fit new prefabricated galvanised bearing plate with holes pre drilledto suit fixed and expansion ends as required. Length of new bearingplate to allow fitting of 3 bolts past bed plate.

b) Weld bearing plate to bottom flange. Weld not to extend past bedplate.

c) Drill bottom flange and grind smooth all burrs.d) Install new bolts.e) Plug and weld up rivet holes.f) Prepare for patch painting.

See detail D shown in Figure 7.6c.

Alternative Option

Fit the new, prefabricated, galvanised bearing plate. Fixing bolts are to be inaccordance with one of the alternative details shown in Figure 7.6a. Tighten thefixing bolts.

If epoxy filler was applied, use the bolt tightening to squeeze the epoxy into anyvoids. Ensure that the bearing plate remains precisely parallel to the girder flangeso that it will sit evenly on the bed plate when the girder is lowered.

Ensure that the bearing plate edges and attachment bolt holes align precisely withthe guides and bolt holes of the bed plate.

7. At the expansion end only apply a liberal layer of lithium disulphide grease tothe underside of the bearing plate.

8. Lower the girder(s) onto the bed plates, checking for proper fit. If epoxy fillerwas used, do not lower the girder(s) until the epoxy has cured.

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9. Fit new attachment bolts in accordance with one of the alternative detailsshown in Figure 7.6a, Figure 7.6b and Figure 7.6c.

7.6.6 Alternative details

Several alternative arrangements for securing the new bearing plate and for theattachment bolts are shown in Figure 7.6a, Figure 7.6b and Figure 7.6c.

The use of stainless steel for the new bearing plate and fixing bolts could beconsidered if the environment is aggressive. Using stainless steel will also avoid theminor problems associated with galvanising zinc entering tapped holes.

For 350 grade bearing plate, a long thread engagement in a tapped hole (1.5 xdiameter) is required with high strength bolts to develop adequate tension capacity.Where the thickness of the bearing plate is less than the required threadengagement and cannot be increased, use a high strength structural steel such asBisalloy 80 for the plate. With this material the thread engagement is to be equal tothe screw diameter.

7.6.7 Action to avoid or minimise recurrence

Routine maintenance to the paint system and to clean dirt and debris from thebearing area. Ensure that longitudinal movement of the expansion end is notprevented.

7.6.8 Special considerations and effects of repair

None.

7.6.9 Follow-up inspection and testing

Programmed inspections only.

Check all bolts for tightness during routine inspections.

7.6.10 Drawing list

Figure 7.6a, Figure 7.6b and Figure 7.6c.

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7.7. Repairing cracked and broken wind brace welded connections

7.7.1 Description of defect

Cracked and broken wind brace members that have been welded at end and centre(main girder) connections.

7.7.2 Description of repair

The repair involves removing welded area of wind brace and connecting new windbrace using gusset plates and bolting.

If broken wind brace is in good condition it may be re-used.

7.7.3 Engineering discussion

In bridges with flat bar wind braces consideration should be given to replacing flatbars with angles.

If flat bars are to be replaced with angles, carry out design check to determine sizeof angles to be used.

Design new gusset plate to suit end connection bolts.

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7.7.4 Procedure outline

1. Prepare new gusset plates.

2. Remove cracked/broken wind brace member by oxy-fuel cutting. Do notallow the cutting flame to damage the main girder flange. Leave cut areaproud if necessary.

3. Grind smooth after removing brace member.

4. Mark flange for location of bolts.

5. Drill flange and grind smooth all burrs.

6. Mark and drill new wind brace, grinding smooth all burrs.

7. Install new wind brace. Fill voids and pitting -see sub procedure 5.4. Fitnew bolts in accordance with sub procedure 5.2.

8. Prepare for patch paint.

7.7.5 Sub procedures required

Ref 5.2.2.1 Oxy-fuel cutting.

Ref 5.2.2.3 Prepare the hole for the bolts.

Ref.5.2.2.4 Install the bolt.

7.7.6 Drawing list

Figure 7.5 Detail B

8. Repairing fatigue damage

8.1. Intercepting fatigue cracks

8.1.1 Description of defect

Fatigue cracks in any steel element.

8.1.2 Description of action

Drill a hole at the tip of a fatigue crack and install a tensioned bolt in the hole. Thisprocedure is not a repair as such, but a course of action that may delay propagationof fatigue cracks.

8.1.3 Engineering discussion

Fatigue cracks occur in a properly designed structure when it nears the end of itsdesign life or in poorly designed details where unanticipated high stress levels orfatigue initiation points occur.

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The progress of fatigue cracks is not easily halted other than by changing thestructural behaviour of the part to dramatically reduce or eliminate the tensilestresses at the crack location. (Refer to procedure 8.2 for an example.) The pre-compression of the region near the crack tip by the tensioning of a bolt has beenfound to inhibit crack propagation.

Warning:

Procedure 8.1 may be used to delay propagation of a fatigue crack, but is unlikely tobe a permanent solution.

After carrying out this procedure, the crack site must be regularly monitored todetect new cracks emerging from the hole perimeter. This is particularly important innon-redundant structures where sudden propagation of a crack will lead to collapse.

8.1.4 Sub-procedures required

None.

8.1.5 Procedure outline

1. Determine the position of the end of the fatigue crack by magnetic particletesting, close visual inspection or other suitable means.

2. Drill a hole of at least 20mm diameter to intercept the crack. Locate thecentre of the hole at the observed crack tip. The preferred hole size is 25 to26mm to suit an M24 Bolt.

3. Use magnetic particle testing on the inside of the hole to confirm that thereare no other cracks around the perimeter of the hole other than the entrycrack, i.e. confirm that the tip of the crack has been drilled out.

4. Install and fully tension a high strength galvanised bolt in the hole. The boltis to have standard washers under both head and nut.

8.1.6 Alternative details

None.

8.1.7 Action to avoid or minimise recurrence

Not applicable.

8.1.8 Special considerations and effects of repair

Do not paint the inside of the hole or the surrounding area as this may hide newcracks forming at the hole edge.

8.1.9 Follow-up inspection and testing

As there is no guarantee that the above procedure will be effective in inhibiting thecrack propagation, inspections of the defect should continue on the same basis as ifthe procedure had not been carried out.

8.1.10 Drawing list

Refer to detail B in Figure 8.2.

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8.2. Repairing fatigue cracks at connections of coped I-sections

8.2.1 Description of defect

Fatigue cracks in an Ι-section web, commencing from the tensile edge adjacent tothe point where the flange has been stopped. Refer to the detail in Figure 8.2.

8.2.2 Description of repair

The repair comprises:

1. Drilling a hole at the end of the fatigue crack and subsequently installing ahigh strength bolt fully tensioned.

2. Fitting extended connection brackets that bolts to the girder web.

The brackets are to relieve the tensile stresses at the crack and bridge between theconnection bolts and the sound portion of the Ι-sections.

8.2.3 Engineering discussion

Fatigue cracks occur in a properly designed structure when it nears the end of itsdesign life or in poorly designed details where unanticipated high stress levels orfatigue initiation points occur.

A common instance of the latter is the subject of this repair and is illustrated inFigure 8.2.

Where the flanges of an Ι-section are curtailed at a distance from the point ofeffective pinned support, or where there is rotational restraint to the girder end, thebending moment may be significant. With only the web to resist the moment, highlevels of stress result. Furthermore, coping of the web or termination of the flange toweb weld may create a fatigue initiation site.

Drilling a hole at the fatigue crack tip is only a temporary measure. It may or maynot delay further crack propagation.

This repair procedure aims to significantly reduce the tensile stress at the crack siteby fitting steel brackets to bridge between the end connection and the sound sectionof Ι-girder.

The procedure described and the details shown in Figure 8.2 are intended toillustrate the principles of the repair rather than any specific case.

A thorough engineering design and the detailing of the steel bracket and itsconnections are required for each particular case. Note that it may not always bepossible to devise a suitable bracket. As a general principle, new brackets shouldbe substantial in section to keep stress levels low.

The design, fabrication and installation effort required by the repair procedure maybe substantial. Close consideration should be given to complete replacement of theΙ-section (in accordance with procedure 11.1) particularly when the member sizeand/or length is small.

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A bridge possession is normally required to implement this repair as the member isto be disconnected.

8.2.4 Sub-procedures required

Only the principles of the repair are given. Any of the sub-procedures may or maynot be required, depending on the designed details.

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8.2.5 Procedure outline

1. Determine the position of the end of the fatigue crack by magnetic particletesting, close visual inspection or other suitable means.

2. Drill a hole of at least 20mm diameter to intercept the crack. Locate thecentre of the hole at the observed crack tip. The preferred hole size is 25 to26mm to suit an M24 Bolt.

3. Drill other holes in the member to suit the brackets to be installed.

4. Temporarily support the end of the member under repair.

5. Disconnect the end of the member by removing rivets etc. as required to fitthe new brackets.

6. Fit new prefabricated, galvanised brackets in accordance with the designdetails. Install and fully tension all bolts including the bolt through the holeat the crack tip.

7. Prepare for and patch paint new steelwork and areas of existing steelworkto the extent directed in accordance with sub-procedure 5.3.

8.2.6 Alternative details

None.

8.2.7 Action to avoid or minimise recurrence

Avoid similar design details in new bridges.

8.2.8 Special considerations and effects of repair

Depending on the details of the new bracket(s), the fatigue crack may be hidden,preventing ongoing monitoring. The member should be inspected regularly foradequate performance under load.

Note that it may not be possible to design brackets with a long fatigue life.

8.2.9 Follow-up inspection and testing

Programmed inspections to monitor the performance of new connection, theprogress of the original crack if possible and check for cracks in the new brackets.

8.2.10 Drawing list

Figure 8.2.

9. Repairing impact damage

9.1. Description of Defect

Any damage to bridge elements caused by impact from road or rail vehicles.

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9.2. Engineering Discussion

The comments of Section 9 are, in the main, drawn directly from the National Co-operative Highway Research Program Report 271 -"Guideline for Evaluation andRepair of Damaged Steel Bridge Members". It is recommended that this documentbe referred to for further detailed comment on the issues and techniques discussedhereunder.

Steel bridge elements including major components such as girders or trussmembers and minor components such as bracing members are frequently damagedby vehicle impact. Once the damage has been detected repair of the damagedcomponents must be undertaken.

In order to ensure that the repair method adopted is cost effective and restores therequired bridge capacity, the following sequence of actions is required:

1. Inspection of damage2. Assessment of damage3. Selection of repair method

A range of repair methods is currently available. These are shown in Table 9.4 thatcompares appropriateness of repair method with type of impact damage.

It can be seen from the table that many of the repair methods are excluded for"Fracture-Critical Members" (FCM's). These are defined as:

"(a) ...those tension members or tension components of members whosefailure would be expected to result in collapse of the bridge or inability ofthe bridge to perform its design function.

(b) Tension components of steel bridges include all portions of tension membersand those portions of flexural members subjected to tension stress. Anyattachment having a length in the direction of the tension stress greater than100mm that is welded to a tension component of a FCM shall be consideredpart of the tension component and, therefore, shall be considered Fracture-Critical."

(AREA Chapter 15, Section 1.14.2.)

The majority of cases of impact damage encountered by ARTC would be toFCM's, i.e. tension flanges of girders and truss tension members.

The applicable range of repairs in most cases will therefore be reduced to full orpartial replacement of the damaged member, or flame straightening of the memberfollowed by installation of bolted cover plates to fully replace the damaged section.

9.3. Sub-procedures required

Repairs to impact damage can involve all of the sub-procedures defined in Chapter5. Techniques associated with the following procedures may also be appropriatewith minor modification, depending on the form of the impact damage:

Ref 6.1 Repairing flange corrosion in riveted girders.

Ref 6.2 Repairing flange corrosion in rolled or welded girders.

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Ref 6.4 Repairing webs with localised corrosion.

Ref 6.5 Repairing corroded bottom flanges of jack arch bridges.

Ref 7.2 Repairing intermediate web stiffeners with localisedcorrosion.

Ref 7.5 Repairing corrosion of bottom flange bracing connection.

Ref 8.1 Intercepting fatigue cracks.

Ref 10.2 Repairing corroded angle columns (temporary supportavailable).

Ref 10.3 Repairing corroded 4-angle columns (no temporarysupport).

Ref 11.1 Replacing members or elements of riveted members.

Further information on the specific repair techniques relating to impact damage iscontained in the previously referenced Report 271.

9.4. Procedure outline

9.4.1 Inspection of damage

Initial inspection and action

Carry out an initial inspection to ensure safety to the user and to reduce furtherdamage to the bridge. When damage is severe, an experienced structural engineershould make the initial inspection and determine whether to restrict traffic or closethe bridge. Preliminary strengthening should be made immediately to preventfurther damage. Preliminary strengthening may also be made to allow traffic on thebridge. These preliminary actions are normally based on judgment supplemented bybrief calculations. If a severely damaged member is fracture-critical, immediatesteps should be taken to prevent bridge collapse. When a member is damagedbeyond repair, the engineer may recommend at this time to partially or whollyreplace the member. When safety of the user is in question, the bridge should beclosed until it is conclusively determined that traffic can be safely restored.

Inspection sequence and record

Commence inspection with the most critically damaged area first, followed byinspection of other damage in descending order of severity. Inspect the mainsupporting members first. Tension members should be inspected for indication ofcracking. Compression members should be inspected for indications of buckling.When more than one member has been damaged a complete description ofdamage for each member should be given.

Painted surfaces should be visually inspected for cracks. Cracks in paint and ruststaining are indications of cracking in the steel. Heavy coatings of ductile paint maybridge over cracks that are tight. When there is any doubt about ability to inspect forcracks, the paint should be removed. Damaged fracture-critical members should beblast cleaned and magnetic particle inspected.

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All areas inspected, including those areas inspected that did not suffer damage,should be recorded. This procedure aids the decision-making process of what, ifanything, should be done to repair a member.

Monitoring of repairs

Follow-up inspection of repairs shall be made on a regular basis. Members thathave complete restoration should be inspected with the same frequency as thecomplete bridge. Member repairs where there is some doubt regarding strength anddurability should be inspected at more frequent intervals. Repairs to fracture-criticalmembers should receive close consideration with respect to inspection frequency.

9.4.2 Assessment of damage

General

Preliminary assessment of damage shall be made during inspection of damage asdescribed under Section 9.4.1. Final assessment of damage shall involve at leastone experienced engineer.

Strength of damaged member

During assessment of damage, a complete evaluation of strength shall be made.This analysis should determine stress levels in the damaged member, and thesestresses shall be compared to the design stresses. This analysis shall allow for alldamage effects such as reduction of section, member distortion etc. Service loadstress should always be computed. Overload, ultimate load, and fatigue stressesshould be calculated as appropriate. Calculations should consider the effect ofstress range and the fatigue category of the member. All preliminary calculationsand decisions made during the inspection phase shall be reviewed.

Fracture-Critical Members

Fracture-critical members shall receive a more rigorous assessment of damage thannon fracture-critical members. Selection of repair procedures for fracture-criticalmembers shall be more conservative than selecting repair procedures for nonfracture-critical members. In general, crack repairs shall be made with boltedcover plates. If other methods are used, such as welding or flamestraightening, elements shall be fully strengthened by adding new boltedcover plates. Enough new material shall be added so that the damagedmaterial can be neglected in computing strength.

Primary members

Primary members can be classified as compression or tension members. Primarymembers in tension shall be considered to be (classified as) Fracture-CriticalMembers. Tensile areas of members such as tensile portions of girders in bendingare treated as tensile members. Many of the limiting restrictions in this manual applyonly to tension members.

To qualify as a compression member, no combination of loading shall producetension in the portion of the member being repaired. Compression members are notfatigue critical and, therefore, stress range limitations used for tensile members donot apply. Charpy impact toughness requirements apply to tension members only.

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Most crack repairs and partial replacements in compression areas may besatisfactorily done by welding

Secondary members

Secondary members are stressed because of deflection of primary members and/orare stressed because of secondary loads such as wind and earthquake. Secondarymembers that carry compression only shall be assessed and repaired in the samemanner as primary compression members. Tension secondary members may berepaired by flame straightening and hot mechanical or cold mechanicalstraightening. Cracks can be repaired by straightening and welding provided thesteel is weldable. No limitation on maximum strain shall be placed on secondarymembers, provided they can be straightened to allowable alignment.

Straightening of FCMs

Any primary tension member may be straightened but all affected fatigue-criticalareas are to be plated except those areas where straightening has been achievedwithout mechanical assistance.

Edge strain (amount of yielding) can be estimated from table 9.1

Maximum versines (2% yielding on edge)Flange width - mm 300 chord 600 chord 1200 chord

100 4.5 18 72120 3.8 15 60140 3.2 13 51160 2.8 11 45180 2.5 10 40200 2.3 9 36250 1.8 7 29300 1.5 6 24350 1.3 5 21400 1.1 5 18450 1.0 4 16500 0.9 4 14

Table 9.1 - Edge strain (amount of yielding)

Assuming the measured distortion is a circular curve, the edge strain (percent) isgiven by

2400

C

wvS

where

w = flange width,

v= versine

C = chord (all in mm)

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and the radius of curvature by

vL

R8

2

where

L = chord length

V = versine (gap)

Sufficient area is to be added to compensate for the damaged section (in theunlikely event that the damaged member/component happens to fracture). As aminimum, 50% additional area is to be added. This minimum addition is based onthe simple premise that if the member is initially designed for a working stress ofabout 0.5 Fy, the straightened member element could be neglected entirely and themaximum stress would not exceed Fy.

Straightening of compression members

Compression members are not generally subject to fatigue failure but it is critical toensure that buckling does not occur.

Calculation of damage curvature

The assessment of damage to a member and selection of the repair method canbest be accomplished from accurate inspection information. A sufficient number ofmeasurements must be made to apply the proposed guidelines. The assessmentprocess should provide information that can be used to select the appropriate repairprocedure.

The best way to estimate curvature is by measuring versines of short chords.Straight edges (or spirit levels) 600mm or 1200mm long held against the inside ofthe curvature are more convenient than using string lines.

Nicks and Gouges

Nicks and gouges shall be carefully described and photographed. Superficial nicksand gouges can be repaired by grinding smooth. More serious damage to weldablesteel in compression members and secondary members can be repaired by welding.Other cases can usually be repaired by adding bolted cover plates. Requiring partialreplacement due to nicks and gouges is rare.

The distinction between superficial and serious shall be made by stresscalculations. As a guide, superficial nicks or gouges can be taken as thoseresulting in less than 10% loss of section of the affected element.

Cracks

Crack assessment must be preceded by a detailed inspection to locate the cracksand determine their length and width, including visual inspection supplemented withmagnetic particle, or dye penetrant testing. Impact cracks are usually surfaceconnected and ultrasonic testing is not generally necessary. The stress and shockof impact will sometimes cause cracking well away from the area of principaldamage.

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Look for spalling of paint or scale as an indication that some unusual strain hasoccurred at such locations and use as a guideline for areas of detailed inspection.Visual examination is not to be limited to these areas, however, since a crack mayoccur in areas that were shock loaded but were not strained enough to spall thepaint or scale. Visual inspection shall be supplemented with magnetic particleinspection in suspect areas.

Particular attention should be given to the examination of the toes of butt and filletwelds in areas subjected to damage as this is an area where cracks often occur.

Field inspection for cracks is done by magnetic particle, dye penetrant andoccasionally ultrasonic inspection.

9.4.3 Selection of repair procedure

General

Repair solutions can be selected from the following range. A combination of repairprocedures may result in the best repair solution. Refer to Table 9.2.

Straightening procedures need to done with care to prevent over-straightening (iecreating bending in opposite direction) and damage from straightening forces anddevices. Also distortions due to yielding must not be confused with those due torestraints from other members.

Flame straightening

This repair method does not significantly degrade steel properties, but is notgenerally effective where yielding has exceeded about 1%. It may be considered forthe repair of all bent members with the following exceptions:

Do not flame straighten fracture-critical members unless the flame-straightened area is fully supplemented by bolted cover plates.

Do not attempt to flame straighten excessively wrinkled plates or plate withexcessive kinks. It is nearly impossible to flame straighten this type ofdamage.

Hot mechanical straightening

This is a process where heat is applied to all sides of a bent member, and while themember is still hot it is straightened by applying force. Agencies that use this

method restrict the maximum temperature to 640o

C. The results of this type ofstraightening are highly dependent on operator skill. Lack of skill (or care) isfrequently indicated by waviness of edges (especially the convex side of thedamage) and local indentations due to local hot yielding under jacking loads.

It is believed that flame straightening is a superior method and should be used inlieu of hot mechanical straightening for all primary tension members, wherepractical. Hot mechanical straightening may be used on primary compressionmembers or secondary members provided the operators have the skill to produceresults that are free of wrinkles, cracks, bulges, and poor alignment.

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Cold mechanical straightening

Cold mechanical straightening is a process where an accidentally bent member isstraightened by applying force. No heat is used. It is believed that a bridge membercan be cold straightened once without causing significant degradation, provided theplastic strain is limited to 5% nominal strain.

Cold mechanical straightening shall not be applied to member areas that havecracks, nicks, or gouges, or to fracture-critical members. Cold mechanicalstraightening should not be applied to members with low Charpy impact values. It isnot recommended that twisted or rotated members be cold straightened.

Welding

Welding may be used for several types of repair, including defect or crack repair,welding replacement segments into place, and adding straightening plates bywelding. Poorly executed weld repairs in tensile areas can be very dangerous and insome instances may do more harm than good. Fracture-critical members shall notbe repaired by welding unless fully strengthened by additional bolted material.

The steels to be repair welded shall be weldable steels.

Do not weld members with low Charpy impact values unless plated in addition.

Bolting

Bolting may be used as a repair method or as a supplement to other repair methods.Replacement of a damaged element with a new piece of steel fastened with fullytensioned high-strength bolts is regarded as the safest method of repair. Replacingdamaged riveted elements with bolted material may not be excessively difficult andshould be considered.

Fracture-critical members shall be repaired by bolting or repaired by other methodsand fully strengthened by adding new bolted material.

Partial replacement

In some instances damage will be so serious that partial replacement is necessary.This damage includes excessively wrinkled plates, excessive deformation andbends, tears in member elements, and large cracks.

Partial replacement will normally consist of removing the damaged area andreplacement with either a welded insert or a bolted splice insert.

Welded inserts are not recommended for fracture-critical members. Partialreplacement by bolting and welding is an acceptable method, provided thelongitudinal web weld is located in a compression area.

Partial replacements can be used in conjunction with other repair methods, such asflame straightening. For example, a bent member with a crack could be flamestraightened and the crack repaired by bolted cover plates.

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Complete replacement

Complete replacement of a member is normally the most expensive method ofrepair.

If a member is excessively damaged throughout its full length, replacement may bethe only alternative. Other less difficult methods of repair should be carefully studiedprior to selecting complete replacement.

Repair Method to ConsiderDamage Assessment Factors

Fla

me

Str

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teni

ng

Hot

Mec

hani

cal

Str

aigh

teni

ng

Col

dM

echa

nica

lS

trai

ghte

ning

Wel

ding

Fla

me

Str

aigh

teni

ngsu

pple

men

ted

byB

oltin

g

Fie

ldW

eldi

ngsu

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men

ted

byB

oltin

g

Bol

ting

Par

tialR

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cem

ent

Ful

lRep

lace

men

t

Weldable Steel Non-Weldable Steel Low Charpy Impact Values Adequate Charpy ImpactValues Fracture-Critical Member Primary Tension Member * * Secondary Members All Compression Members Tearing and Excessive Wrinkles Primary Tension MemberCurvature Strain MeetsGuidelines

* *

Primary Tension MemberCurvature Strain Does Not MeetGuidelines

Member Curvature Radius Morethan

Member will return to correct position when adjacent membersor joints are straightened

Cracks - Weldable Steel Non Weldable Steel Superficial Nicks and Gouges Grind Defect SmoothNicks and Gouges WeldableSteel

* Flame straightening is recommended

Table 9.2 - Selection of repair method for impact damage

Strength of repair method

Fracture-critical members should be repaired by methods that unquestionablyrestore full strength. These methods may include bolted splices, partial replacementby bolting, and full replacement. All loading capacities, including service load,overload, and ultimate load, should be fully restored, and the service life should befully regained.

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Non–fracture-critical members may be repaired by the same methods used forfracture-critical members. However, other less costly methods should also beconsidered and used as appropriate.

Durability of repair

Durability of repair must be given a high priority. All methods of repair should havedurability equal to or better than the original member. The accessibility of all parts ofa repaired structure for inspection, cleaning, and painting shall be accomplished bythe proper proportioning of repairs and the design of their details. Closed sections,and pockets or depressions that will retain water, shall be avoided. Pockets shall beprovided with effective drain holes or filled with waterproofing material.

9.4.4 Action to avoid or minimise recurrence

Install low clearance warning signs and alternative route signs. Install loading gauges remote from bridge site to warn oversize vehicles. Install crash beams to protect superstructure elements and kerb barriers to

protect substructure elements.

9.4.5 Special considerations and effects of repair

Refer to Section 9.2.

9.4.6 Follow-up inspection and testing

Refer to Section 9.4 Point 3.

Check for growth of cracks where cover plates for repair are less than full sectionrequirements.

10. Repairing stepways and footways structures

10.1. Repairing steel risers and stringers in stepways

10.1.1 Description of defect

Severe corrosion of steel risers and stringers and their connections leading to asignificant loss of cross-sectional area and consequent reduction in strength.

10.1.2 Description of repair

Stringers with severe corrosion to flanges should be replaced. Where severecorrosion is limited to the web, a web cover plate may be welded in lieu of completereplacement.

Risers with severe corrosion are to be replaced entirely with galvanised steelchannels, site welded to stringers.

10.1.3 Engineering discussion

Members should be repaired or replaced when loss of section results in a strengthor stiffness reduction below 75% of which is required at any particular location.

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A simple design check should be carried out to check the strength loss, but thefollowing guidelines may be applied:

Risers: Replace members exhibiting in excess of

= 20% loss in cross-sectional area of both flanges combined,or= 40% loss in cross-sectional area of the web.

Stringers: Replace members exhibiting in excess of 20% loss in cross-sectionalarea of both flanges combined or 30% loss in cross-sectional area ofweb plate. Fit cover plates to webs of members exhibiting between10% and 30% loss in cross-sectional area of the web.

Consideration should be given to complete replacement of all risers or all risers andstringers in stepways where a significant proportion of individual elements wouldrequire replacement.

Although bolted connections have generally been used in this manual as thestandard for steel repair, site welding is the proposed method of connection of newsteel elements in this repair procedure. The locations where welding is required aretypically low stress areas in stepways and fatigue is not usually critical as live loadstress ranges and cycles are small.

Notwithstanding the above, the weldability of the steel is to be checked byappropriate tests or scientific investigations and all completed welds are to bechecked for defects.

Where stringers are to be replaced, adopt the lower end support arrangementillustrated in detail D of Figure 10.1b to keep the structure clear of the ground.

10.1.4 Sub-procedures required

Ref 5.1 Arresting Corrosion

Ref 5.2 Removing Rivets and Replacing with Bolts

Ref 5.3 Patch Painting (including surface preparation)

10.1.5 Procedure outline

Case A - Stringers and risers to be replaced

(Only if cost evaluation shows that total stepway renewal is not the cost effectivesolution).1. Remove precast treads and handrails etc.

2. Remove stringers and risers. Remove rivets securing stringers inaccordance with sub-procedure 5.2.

3. Install new galvanised stringers, fabricated to existing steelwork, exceptuse the lower end support detail as shown in Figure 10.1b. Use galvanisedsplice plates where required to connect stringer segments. Use galvanisedbolts in lieu of rivets.

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4. Prepare new galvanised risers for installation by cutting and trimmingflanges at the ends, all as detailed in Figure 10.1a.

5. Site weld the new risers to the stringers at positions and levels to suit theprecast step units to be used.

6. Prepare for and patch paint at the riser connections and other areas ofsteel to extent directed in accordance with sub-procedure 5.3. Note thespecial preparation required for rough surfaces such as site fillet welds.Where galvanised surfaces are to be painted, use the appropriate paintsystem and surface preparation as described in sub-procedure 5.3.

7. Refit precast treads and handrails using new galvanised or stainless steelbolts and fittings.

Case B - Risers only to be replaced

1. Remove precast treads and handrails etc.

2. Remove risers to be replaced by oxy-fuel cutting adjacent to theattachment to the stringers. Do not allow the cutting flame to burn orotherwise affect the stringers that are to remain. Remove otherattachments supporting risers.

3. Grind smooth the face of the stringer web and expose the base metal forwelding.

4. Prepare new galvanised risers for installation by cutting and trimmingflanges at the ends, all as detailed on in Figure 10.1a.

5. Site weld the new risers to the stringers at positions and levels to suitprecast step units to be used.

6. Prepare for and patch paint at the riser connections and other areas ofsteel to extent directed in accordance with sub-procedure 5.3. Note thespecial preparation required for rough surfaces such as site fillet welds.Where galvanised surfaces are to be painted, use the appropriate paintsystem and surface preparation as described in sub-procedure 5.3.

7. Refit precast treads and handrails using new galvanised or stainless steelbolts and fittings.

Case C - Risers to be replaced and stringer web to be plated

1. Remove precast treads and handrails etc.

2. Remove risers to be replaced by oxy-fuel cutting adjacent to theattachment to the stringers. Do not allow the cutting flame to burn orotherwise affect the stringers that are to remain. Remove otherattachments supporting the risers.

3. Grind smooth the inner face of the stringer web to remove any remainingsteel from the cross member and any other protrusion that would interferewith the cover plate. Where rivets project through web, provide holes in thecover plate.

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4. Remove all loose rust from the face of the web to be plated by mechanicalwire brushing. Fill all areas of pitting and all depressions with epoxy filler tocreate a smooth even surface for mounting the cover plate, all inaccordance with sub-procedure 5.4.

5. Fit prefabricated, galvanised 8mm web cover plates and fix to the stringersby site welding, all in accordance with the details in Figure 10.1b.

6. Prepare new galvanised risers for installation by cutting and trimmingflanges at the ends, all as detailed in Figure 10.1a.

7. Site weld the new risers to the stringers at positions and levels to suitprecast step units to be used.

8. Prepare for and patch paint at the riser connections and other areas ofsteel to extent directed in accordance with sub-procedure 5.3. Note thespecial preparation required for rough surfaces such as site fillet welds.Where galvanised surfaces are to be painted, use the appropriate paintsystem and surface preparation as described in sub-procedure 5.3.

9. Refit precast treads and handrails using new galvanised or stainless steelbolts and fittings.

10.1.6 Alternative details

None.

10.1.7 Action to avoid or minimise recurrence

Routine maintenance to remove build up of dirt and debris, particularly at locationsof site welds.

10.1.8 Special considerations and effects of repair

None.

10.1.9 Follow-up inspection and testing

Programmed inspections only.

Pay particular attention to inspection for corrosion at site welds.

10.1.10 Drawing List

Figure 10.1a and Figure 10.1b

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10.2. Repairing corroded angle colums(temporary support available)

10.2.1 Description of defect

Severe corrosion of multiple angle columns resulting in significant loss of cross-sectional area. This procedure covers the case where the structure can betemporarily supported, allowing complete removal of the column.

10.2.2 Description of repair

The repair involves complete or partial replacement of the column with a galvanisedUniversal Column (UC) section that is less prone to corrosion damage. Concretefootings with significant damage are to be repaired or rebuilt in conjunction with thisrepair.

10.2.3 Engineering discussion

An engineering assessment to determine the necessity of the repair and the extentof column replacement should be carried out.

In the absence of an engineering assessment, adopt the following guideline.

Replace columns or segments of columns where the maximum loss of cross-sectional area exceeds 20%.

It should be noted that columns comprising 2 and 4 angles often have a muchgreater axial load capacity than is required, provided they are adequately braced.On the other hand, columns supporting structures that have had concrete overlaydecks added may be highly loaded.

If severe corrosion has occurred over a significant portion of the existing column,complete replacement is recommended. Partial replacement of the lower part of thecolumn should only be adopted if severe corrosion is limited to the lower quarter,with the remainder in good condition and likely to remain so.

The top connection of the replacement column to the supported structure or theremainder of the column must be detailed to ensure proper load transfer.

Where concrete footings to columns have deteriorated significantly and are notrepairable, they should be rebuilt in reinforced concrete. The ground bearing area isnot to be less than that of the existing footing.

Temporary support must be provided at adjacent columns that become unbracedduring the repair. The axial load capacity of such columns is significantly reducedby the disconnection of braces.

Refer to Table 10.1 for replacement column sizes.

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To replace angle sizeUC size2 Leg 4 Leg

150 UC 23 102 x 108 x 8 76 x 76 x 5150 UC 30 127 x 127 x 8 76 x 76 x 8150 UC 37 127 x 127 x 10 76 x 76 x 10200 UC 46 127 x 127 x 16 89 x 89 x 10200 UC 60 152 x 152 x 12 102 x 102 x 12250 UC 73 152 x 152 x 16 102 x 102 x 12310 UC 97 200 x 200 x 16 127 x 127 x 12

Table 10.1 - Replacement UC sizes

10.2.4 Sub-procedures required

Ref 5.2 Removing Rivets and Replacing with Bolts

Ref 5.3 Patch Painting (including surface preparation)

10.2.5 Procedure Outline

1. Install temporary supports to allow removal of the column.

2. Remove the rivets connecting bracing to the column then remove thecolumn. If the concrete footing is to remain, cut a pocket at the base of thecolumns to permit oxy-fuel cutting of the steel 50mm below the concretesurface.

3. Repair the existing footing or build a new footing in reinforced concrete ifrequired. Drill holes for hold-down bolts.

4. Install the new column and complete the base detail as shown in Figure10.2. Connect to structure or remainder of column above

5. Trim bracing members to size and drill new holes for connection to the newbracing cleats.

6. Prepare for and patch paint new and existing steel to the extent directed allin accordance with sub-procedure 5.3.

10.2.6 Alternative details

None.

10.2.7 Action to avoid or minimise recurrence

The proposed details minimise future corrosion if routine maintenance is carried out.

10.2.8 Special considerations and effects of repair

None.

10.2.9 Follow-up inspection and testing

Routine inspections only.

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10.2.10 Drawing list

Figure 10.2.

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10.3. Repairing corroded 4-angle colums(no temporary support)

10.3.1 Description of defect

Severe corrosion of 4-angle column resulting in significant loss of cross-sectionalarea. This procedure covers the case where the column must continue to carry loadduring the repair as temporary support of the structure is not possible.

10.3.2 Description of repair

The repair involves progressive replacement of each angle of the column, in part orin full. Only one angle is removed from the column at any time. The remainingangles support the dead load of the structure. Partial replacement involves splicingnew, galvanised angle segments to the existing steelwork by bolting or, wherepermissible, welding.

10.3.3 Engineering discussion

An engineering assessment to determine the necessity of the repair and the extentof column replacement should be carried out

In the absence of an engineering assessment, adopt the following guideline.

Replace columns or segments of columns where the maximum loss of cross-sectional area exceeds 20%.

It should be noted that columns comprising 2 and 4 angles often have a muchgreater axial load capacity than is required, provided they are adequately braced.On the other hand, columns supporting structures that have had concrete overlaydecks added may be highly loaded.

It must be recognised that the bracing system interconnecting columns is oftenessential to achieve the required axial load capacity in the columns. The repairprocedure has been devised to ensure that the column under repair remains bracedat all times. Only by an engineering assessment of the particular case can it bedetermined if bracing can be disconnected during the repair.

Where concrete footings to columns have deteriorated significantly and are notrepairable, they should be rebuilt in reinforced concrete. The ground bearing areaand founding level are not to be less than that of the existing footing.Bolting is the preferred method of connecting new, galvanised angle segments toexisting steelwork. Welded splices, involving full penetration butt welding of theangles, may be used where it can be determined by analysis and testing thatexisting steels are weldable.

The preferred location for bolted splices is immediately above or below bracingconnection points.

10.3.4 Sub-procedures required

Ref 5.1 Arresting Corrosion

Ref 5.2 Removing Rivets and Replacing with Bolts

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Ref 5.3 Patch Painting (including surface preparation)

Ref 5.4 Filling Voids

Ref 5.5 Sealing Interfaces

10.3.5 Procedure outline

1. Cut a pocket in the concrete footing around the base of the column asshown in Figure 10.3b. If welded splices are to be adopted, excavatesufficient to expose an uncorroded section of column.

2. Drill holes for hold-down bolts. Commence the procedure described indetail in Section 10.3.6 to replace the angles (segments) one by one.

As each of the 4 angle segments is positioned, complete the base connection (HDbolt and base plate or welded splice) and the upper splice connection (bolted orwelded). The bolts in the bolted splice connection will need to be removed andreinserted as described for bracing and packing bolts during the procedure.

Mortar is to be packed under each individual base plate before the next angle isremoved to ensure adequate transfer of load.

Fill voids at the heel of splice angles as they are installed. Refer to Section D ofFigure 10.3a.

3. Seal any open interfaces between individual base plates and at spliceangles or at backing bars as required. Refer to sub-procedure 5.5.

4. Apply epoxy filler between the angles at the base, profiled as shown inFigure 10.3c to promote free drainage of water from column base.

5. Prepare for and paint new steelwork and areas of existing steelwork to theextent directed in accordance with Sub-procedure 5.3.

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10.3.6 Procedure for removing angles one-by-one

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10.3.7 Alternative details

Details of bolted and welded splice alternatives have been provided.

10.3.8 Action to avoid or minimise recurrence

Routine maintenance to remove built-up dirt and debris between angles, at the baseand at packs etc. fitted between angles.

Epoxy fill between the angles at the base as illustrated in Figure 10.3c to promotefree drainage of water from column base.

10.3.9 Special considerations and effects of repair

None.

10.3.10 Follow-up inspection and testing

Programmed inspections only.

10.3.11 1 Drawing list

Figure 10.3a, Figure 10.3b, Figure 10.3c.

11. Complete replacement of members

11.1. Replacing members or elements of riveted members

11.1.1 Description of defect

Any impact damage, severe corrosion or fatigue cracking of a member wherecomplete replacement of the member or, in the case of riveted members, one ormore components of that member is feasible.

11.1.2 Description of repair

Complete replacement of the member or element of a riveted member.

11.1.3 Engineering discussion

An engineering assessment to select the appropriate repair for a defect maydetermine that the best option is the complete replacement of the members or theelement of a riveted member.

11.1.4 Sub-procedures required

Ref 5.2 Removing Rivets and Replacing with Bolts

Ref 5.3 Patch Painting (including surface preparation)

11.1.5 Procedure outline

1. Determine the size, shape and layout dimension for bolt holes by carefulmeasurement on site.

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2. Fabricate and galvanise the replacement member or elements.

3. Fit any temporary bracing or support members required.

4. Unbolt connecting bolts or remove connecting rivets in accordance with sub-procedure 5.2. Remove the member or component.

5. Prepare the area of interface to the new member or element by cleaning,grinding and painting if required.

6. Fit the new member or element and complete the bolted connections inaccordance with sub-procedure 5.2.

7.7. Prepare for and patch paint new and existing steelwork to the extent directed

in accordance with sub-procedure 5.3.

11.1.6 Alternative details

The new member and its connections may differ in detail from the member itreplaces provided it has been designed for the appropriate loads and effects andthat the capacity of the structure or part of the structure is not reduced.

HUCK BOM blind fasteners may be used where there is access to only one side ofthe connection.

11.1.7 Action to avoid or minimise recurrence

None

Special considerations and effects of repair

None.

11.1.8 Follow-up inspections and testing

Programmed inspections only.

11.1.9 Drawing list

None.

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Bridge Repair Manual

Part 3Concrete Repairs

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12. Introduction

12.1. General

This Section aims to provide a simple guide to understanding the causes andmechanism of concrete deterioration, identification of common types of defects andselection of suitable repair materials and techniques. It is limited to repair methodsthat can be easily carried out by maintenance personnel and general contractors. Itsapplication is limited to reinforced concrete structures only. The methods givenherein should not be used for repairing prestressed concrete structures.

Repairs that appear to be difficult and extensive due to severe deterioration and thatmay require technical investigation and special equipment should be arrangedthrough organisations experienced and skilled in testing and repair of concrete.

Almost all concrete structures are subject to some kind of deterioration. The damagecaused by the deterioration may be minor, that need not even be repaired, or it maybe very significant requiring immediate attention. Some defects may appear minorin the beginning but if left untreated could grow into major repair operations later.

It is therefore important to understand the mechanism of deterioration, what types ofdefects can develop, how to assess whether a defect is minor or significant and thento decide how to repair the defect and what are the most appropriate materials andrepair methods.

12.2. Health and safety

It must be emphasised that in all types of repair and construction work, health andsafety of all personnel is of paramount importance.

Attention is therefore drawn to Chapter 3 "Health and Safety" that highlights theprocedures for ensuring the safety of workers, and public as well as theenvironment.

12.3. References

The subject matter of concrete repairs has been obtained from a number of sources.These, as well as other references that could be useful for additional and detailedinformation, are given at the end of the Section. The assistance obtained from thevarious references is gratefully acknowledged.

13. Deterioration of concrete

13.1. Factors affecting deterioration

Deterioration of concrete is affected by the following factors:

Quality of the constituent materials (cement, sand, aggregate, admixturesand water used in the manufacture of concrete).

Environmental conditions (exposure to air, water, chemicals, industrialpollutants, marine condition, frost etc).

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Physical properties of concrete (permeability, compressive strength, density,cement content, shrinkage characteristics).

Standard of workmanship during construction (fixing of formwork andreinforcement, placing, compaction and curing of concrete).

Concrete cover to steel reinforcement.

Design practice (mix design, detailing of reinforcement and concrete cover,practicality of construction).

13.2. Causes of deterioration

The main causes of deterioration of concrete are summarised below:

13.2.1 Corrosion of reinforcement

Rusting or corrosion of reinforcement is one of the major causes of deterioration ofreinforced concrete. Corrosion involves a combination of processes, mainlycarbonation and chloride contamination, leading to de-passivation of steel and itssubsequent corrosion by electrolytic reaction.

In theory, the steel reinforcement is protected from rusting by a film of oxide that isstable in the alkaline environment of the concrete surrounding it. The alkalinity isprovided by the free calcium hydroxide (lime) present in the Portland cement. Theprocess of corrosion is initiated by de-passivation of the steel, i.e., breakdown of theprotective oxide layer due to degradation of the alkaline environment. The alkalinityin concrete may be reduced by either of the following causes:

Leaching out of the free lime by water if the concrete is porous.

Carbonation: Penetration into concrete of carbon dioxide present in theatmosphere. The carbon dioxide dissolves in the pore water of the concreteand reacts with the free calcium hydroxide to form neutral calcium carbonate.This reaction progressively lowers the alkalinity of concrete that results inremoval of the passive oxide layer from the steel. The carbonation rate isvery dependent on the concrete quality. Concrete with high water/cementand high porosity carbonates very rapidly.

Chloride contamination: The chlorides can come from a number of sourcesincluding contaminated aggregates, admixtures such as calcium chloride andexposure to sea water, salt spray or saline water. The chlorides in the porewater within the concrete form an electrolyte and the chloride ions locally de-passivate the steel reinforcement by breaking down the protective oxidelayer even in highly alkaline concrete.

The depassivation of steel creates the environment that leads to corrosion of steel inpresence of moisture, oxygen and an electrolyte. An electrolyte can be formed byvery small quantities of carbon dioxide, sulphates or chlorides in the pore water.The electrolytes set up an electrolytic cell action between anodic and cathodic

regions formed on the steel. The electrons from the Fe++

ions flow from the anode

through the steel to the cathode where OH-

ions are formed. The OH-

ions flow from

cathode through the concrete to the anode where they combine with the Fe++

ions to

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form the complex hydrated iron oxides and hydroxides known as rust. (See Fig.13.1).

The corrosion process is usually slow but always progressive. The products ofcorrosion occupy a volume greater than the parent metal. This volume increasegenerates high internal pressures that cause debonding, cracking and eventuallyspalling of the concrete.

The corrosion is therefore primarily an electrical process that results in formation ofrust at the anode regions on the reinforcement bars. (See Fig. 13.2).

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13.2.2 Sulphate Attack

Sulphate attack is initiated by sulphates that may be present in ground water or areformed by penetration into concrete of sulphur dioxide from the air, particularly inareas of industrial pollution. The sulphates react with calcium hydroxide to formgypsum (CaSO4) that subsequently reacts with tricalcium aluminate (C3A) of thecement to form a swelling sulphoaluminate substance known as ettringite. Concreteaffected by sulphate attack expands, initiating cracking and spalling that providesaccess to reinforcing steel for the very aggressive sulphate ions resulting incorrosion of steel.

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13.2.3 Alkali aggregate reactivity

Certain aggregates can react with the alkali present in cement to form a gel thatswells by absorbing moisture and cracks the surrounding concrete. As the reactionadvances cracks extend over the surface in a random "mud crack" pattern andpopouts, appearing first on the most weathered surfaces. Alkali aggregate reaction(AAR) also manifests as closing up of gaps in concrete and development of cracksalong stress lines in the vicinity of concentrated loads such as bearings andprestressed anchorage zones. In the long term the gel exudes through the cracksas white efflorescence and the concrete shatters into small blocks or along stresslines, but may be held together by steel reinforcement. The effects of AAR areunsightly and structurally debilitating.

13.2.4 Shrinkage, thermal and load effects

Cracking is induced in concrete structures when free movement due to shrinkage ofconcrete and thermal expansion and contraction is restrained, even under simpleloads. Thermal effects include those occurring during the heat of hydration in freshconcrete poured in restrained locations (eg against "cold" joints). Cracking resultswhen the new concrete cools and shrinks.

In continuous structures temperature gradients may also cause flexural cracking dueto large sagging moments produced over the supports. Similarly, differentialshrinkage between precast girders and cast-in-place deck of continuous bridgesmay result in cracks in the region of hogging moments.

Cracks produced by these effects should have been allowed for in the design, andare most likely to occur due to bad design, poor detailing and poor construction. Thestructural significance of these cracks should be checked by a structural engineerprior to any treatment that may range from no action to external strengthening. If theconcrete is sound such cracks should have little effect on corrosion unless they runalong reinforcing steel or are very large.

13.2.5 Frost and salt attack

Frost attack is unusual in Australia but salt attack is more common and will occurwhere concrete is in intimate contact with sea, salt lakes or high salinity soils.

Under frost the water in the pores of concrete freezes and expands generating highinternal pressures that shatter the concrete surface. Salt in a saturated solution canalso seep into concrete pores and crystallise by evaporation of the water. Thecrystals expand and generate high pressures that spall the surface of the concrete.Both effects are pronounced in poor quality concrete and lead to corrosion of steel.

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13.2.6 Impact forces

Impact damage can be caused in bridge structures by:

Collision of, or glancing blows from, motor vehicles against piers,abutments and parapets.

Derailment of trains.

Overheight vehicles striking against the underside of the bridgesuperstructure.

Impact of heavy floating logs carried by rapid flowing streams against thebridge structure.

This type of damage generally causes cracking and spalling of concrete with orwithout exposure of reinforcing steel. Severe impact may also result in rupture orfracture of members and collapse of the bridge.

Impact damage should be repaired promptly before the reinforcement has started torust and before the damaged surfaces are affected by carbonation or contamination.(See Fig. 13.5).

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13.2.7 Overloading

Overloading of bridge structures may occur due to vehicles with above legal limitweight, increase in train loads since the construction of bridges, extremes oftemperature causing excessive movements, high temperature differentials within thestructure, high winds, excessive build up of road metal or ballast on the deck or buildup of flood debris against the structure. Overloading can cause cracking of concretemembers. Excessive overloading may result in fracture of members and collapse ofbridge. Cracks that have formed as a result of accidental overload will tend to bevery fine after the load has been removed and often need no treatment. Crackswider than 0.3 mm may need to be sealed.

For increased train loads, strength of all components of the bridges should beassessed by structural calculations.

13.2.8 Faulty construction

Faulty construction is one of the most common causes of early deterioration.Common construction faults include:

14. Formwork not cleaned out properly (pieces of timber, nails and debrisembedded in finished concrete).

Formwork not made watertight (honeycombed concrete due to loss of

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cement grout).

Inadequate compaction (voids in concrete). (See Fig. 13.6).

Over compaction (laitance on top surface leading to scaling).

Lack of sufficient concrete cover to steel either by failure to fix thereinforcement correctly or due to poor design.

Inadequate and insufficient curing.

14.1.1 Deterioration at joints

Joints in structures are specially vulnerable to deterioration for several reasons:

They can be difficult to construct and the concrete at a joint may lackcompaction.

They may act as paths for the entry of salty water or carbon dioxide.

They may fail to work as joints forcing the concrete to crack at an adjacentplane of weakness (eg at the end of dowels or at the fin of a waterstop).

They may not be intended to be active joints (eg construction joints) but maysubsequently become active without having any provision for sealing.

These faults will eventually result in rusting of reinforcement after the concrete hasbecome carbonated. If repair action is taken quickly, before the reinforcement has

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started to corrode, it is possible to prevent or greatly reduce the extent of damagefrom these causes.

15. Types of defects

15.1. IntroductionCommon defects that occur in concrete structures and need repair action are asfollows:

Cracking Spalling Scaling - Cement rendering breaking away Delamination Leaching Rust stains Honeycombing Fire damage Dampness Leaking joints Breaking up of repairs Shattering - Bearing pads common in all bridges Crushing - Bearing pads common in all bridges

15.2. Cracking

Cracking can be an important indicator of deterioration taking place in concrete andpossible corrosion of reinforcement steel depending on the size, extent and locationof the cracks. Because the significance of each type of crack is different, it isimportant to distinguish between them. Seven types of cracks generally occur.

Longitudinal cracks (formed in hardened concrete)

These cracks run directly under or over and parallel to reinforcing bars and arecaused by build up of rust on the reinforcement. Eventually they will lead to spallingand complete loss of concrete cover. Longitudinal cracks cannot be treated withoutremoval of the deteriorated concrete and renewing the cover. (See Fig. 14.1).

Transverse cracks (formed in hardened concrete)

Cracks transverse to the reinforcement are caused by concrete shrinkage, thermalcontraction or structural loading. The width and distribution of these cracks iscontrolled by the amount and disposition of the reinforcement.

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Where there is no secondary reinforcement (as in beams), these cracks will only betransverse to the main reinforcement and are harmless unless they are very wide orthe environment is exceptionally aggressive. (See Fig. 14.2).

Where reinforcement runs in two directions at right angles (as in slabs), cracks thatare transverse to secondary bars will tend to coincide with the main bars becausereinforcement of the larger size tends to act as a crack inducer. Unless thesecracks are treated soon after they appear they could cause rusting of reinforcementand further deterioration.

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Shear cracks (formed in hardened concrete)

Shear cracks are caused by structural loading or movement of supports (eg due tofoundation settlement) or lateral displacement of frames and columns. Occurrenceof shear cracks will result in reduced strength of a member. They may also causerusting if left untreated.

Plastic shrinkage cracks (formed in unhardened concrete)

In the construction of concrete surfaces such as floor slabs or decks, loss ofmoisture from the surface due to rapid evaporation causes cracks on the surface.These cracks are harmless unless the concrete slab will later be exposed to salt orother contamination that would result in deterioration. (See Fig. 14.3).

Plastic settlement cracks (formed in unhardened concrete)

These cracks develop during construction when high slump concrete is used,resulting in settlement of the solids and bleeding of water to the top especially indeep sections. Settlement cracks form at the top where the reinforcement hassupported the aggregate and stopped it from settling, while water collects under thereinforcement displacing the cement grout and leaves the steel unprotected. Thecracks form longitudinally over the reinforcement and are a common cause ofserious corrosion. (See Fig. 14.4).

Map cracks

Map cracking is caused by alkali-aggregate reaction over an extended period oftime. The cracks are internal in origin and result in breaking up of concrete and lossof strength.

Surface crazing

Craze cracks are fine, random cracks or fissures that develop on concrete surfaces.They result from shrinkage of the concrete surface during or after hardening and are

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caused by insufficient curing, excessive finishing or casting against formwork. Theirsignificance is mainly aesthetic. (See Fig. 14.5).

15.3. Spalling

Spalling is defined as a depression resulting from detachment of a fragment ofconcrete from the larger mass by impact, by action of weather, by overstress or byexpansion within the larger mass. The major cause of spalling is expansion resultingfrom corrosion of reinforcement. Spalling caused by impact can weaken thestructure locally and expose the reinforcement to corrosion. (See Figs. 14.6 and14.7).

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15.4. Scaling

Scaling of concrete surfaces is defined as local flaking or peeling away of portions ofconcrete or mortar near surface. As the deterioration continues, coarse aggregateparticles are exposed and eventually become loose and are dislodged. (See Fig.14.8).

Scaling occurs where the surface layers of concrete are not finished dense andhomogenous. Poor finishing practices result in weak layers of grout at the top ofconcrete surfaces that easily peel away by weathering or abrasion.

Light scaling refers to the loss of surface mortar only without exposing coarseaggregate. Medium and severe scaling involves loss of mortar with increasingexposure of aggregate. Very severe scaling refers to loss of coarse aggregatetogether with the mortar.

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15.5. Delamination

Delamination refers to separation of layers of concrete from bridge decks, beams orwalls at or near the level of the top or outermost layer of reinforcing steel andgenerally parallel to the surface of the concrete member. The delamination is notpossible to identify visually as the concrete surface appears intact on the outside. Itcan, however, be detected by tapping the surface with a heavy rod or hammer whena hollow or drumming sound is given off indicating the separation of concrete fromthe reinforcement.

With practice, this sound can be identified accurately enough to mark the affectedarea on the surface of the concrete.

The major cause of delaminations is the expansion resulting from corrosion ofreinforcing steel. As soon as delamination is detected steps should be taken toascertain the cause of corrosion including laboratory testing of concrete samplesand appropriate repair action initiated. If a successful repair is not made, concreteabove the delamination interface will eventually become dislodged and a spall willresult.

15.6. Leaching

Leaching or efflorescence is the white deposit of salts or lime powder formedcommonly on the underside of deck slabs or vertical faces of abutments, piers andwingwalls. It is caused by surface or subsoil water leaching through the cracks andpores in the concrete. The water dissolves the lime and other salts in concrete (or,may already be contaminated with salts from the subsoil). The dissolved substancesare deposited as white powder on concrete surface after the evaporation of water.(See Fig. 14.9).

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15.7. Rust stains

Brown or rust coloured stains on concrete surface indicate corrosion of steelreinforcement. (See Fig. 14.10).

15.8. Honeycombing

Honeycombing is lack of mortar in the spaces between coarse aggregate particles.It is caused by insufficient compaction or vibration during placement of concrete andresults in porous and weak concrete. The voids also provide channels for ingress ofwater, oxygen and corrosive agents such as carbon dioxide, chlorides and sulphatesthat will eventually cause corrosion of steel reinforcement. (See Fig. 14.11).

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15.9. Dampness

Moderately wet or moist areas of concrete indicate penetration of moisture and willeventually lead to corrosion of reinforcement and deterioration of concrete. Thesource of moisture is often from ponding or improper drainage over or in the vicinityof the structure. This should be investigated and remedial measures taken asappropriate.

15.10. Leaking joints

Deterioration or loss of sealants and jointing materials from the joints and/ordeterioration or lack of waterproofing membranes results in penetration of waterthrough the joints. Apart from being a nuisance, it causes ugly stains and growth ofalgae around the joints. The penetrating water along with dissolved contaminantswill also find a way into porous or weak concrete leading to deterioration of thestructure.

15.11. Breaking up of repairs

Past repairs are indicative of problems in the structure. The repairs should bemonitored during inspections. The condition of the repair or patch will usuallyindicate whether the underlying problem has been solved or is still continuing.Cracking, delamination, spalling or rust stains in or around the repair indicate thatthe problem still exists and further investigation and repair are needed.

16. Assessment of deterioration

IMPORTANT NOTE:The most important matter in any assessment of damage is to establish if the strength andstability of the structure are adversely affected. Where safety of a structure is in question,professional advice should be sought immediately for the protection of the structure aswell as its users against further damage, collapse or injury. (See Fig. 15.1).

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WarningEven the most basic joint depends on the concrete cover for its strength.Before removing any concrete from a load bearing structure consider carefully whetherthe concrete you propose to remove is providing essential support for the structure.If it could be, support the structure first.

16.1. General

To successfully repair a deteriorated concrete structure it is essential to identify thecause, extent and rate of deterioration of concrete and whether or not the cause isstill active.

A step by step procedure for assessing deterioration is given below. This procedureincludes a number of simple tests that can be easily carried out on site. It is notessential to carry out all the tests and judgement should be used in applying thetests according to the severity of the problem at hand.

It is also recognised that resources for carrying out these tests may not be availableand detailed investigation may have to be entrusted to specialist firms or consultingengineers who have appropriate expertise to establish the causes of deteriorationand advise on what repair action should be taken.

16.2. Assessment procedures

1. Before proceeding, assess if detailed examination of the damage ordeterioration will require track closure, power outage, pedestrian and trafficrestrictions, assistance from police and utility authorities (Gas, Electricity,Telecom, Water Board), worksite protection, special equipment (ladders,cherry pickers) and any special safety measures.

2. Study previous investigation and repair reports available, if any. Examinethe condition of the past repairs to determine whether they have beensuccessful or if the deterioration is growing worse.

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3. Carry out a visual inspection of the structure and, if necessary, use handmagnifiers, binoculars and telephoto photography to record the type andextent of deterioration. Estimate the crack widths. If possible, ascertain theobvious causes of deterioration such as reinforcement corrosion, poordrainage, environmental conditions, accidental damage etc.

4. Examine for hollowness and delaminations by tapping with a hammer,medium size spanner or a steel rod. Use chain-drags on slabs. Assess andmark out suspected areas of hollowness and delaminations.

5. Ascertain if the cracks are "live", that is, their width changes under thermal orstructural loading. This can be detected with a mechanical strain gauge heldon gauge discs glued to the concrete surface. Cracks that are due to appliedload will move immediately the load is changed (eg. under traffic passingover the bridge). Cracks due to thermal movement move when thetemperature of the element alters. Measurements made three or four times aday should establish whether a crack is live or not.

6. Estimate the concrete cover to reinforcement using electromagnetic covermeters or by actual measurement where concrete is broken andreinforcement is exposed. Check if the cover provided is adequate for theexposure conditions, or is as per drawings (if the drawings are available).

7. Testing for carbonation: Break off small pieces of concrete from differentareas of the structure using hammer and cold chisel and test freshly exposedconcrete surfaces by spraying with 2 percent solution of phenolphthalein inalcohol. This pH indicator solution will change colour according to thealkalinity of the concrete. The solution remains pink and is easily visible onconcrete that has retained its alkalinity but becomes colourless on concretethat has lost its alkalinity by carbonation. The test will thus indicate the depthto that the concrete has been carbonated from the surface.

8. Testing for chloride contamination: To determine the chloride content ofconcrete, samples are obtained by drilling holes in the concrete andcollecting the dust produced. (If there is any surface salt built up, it must beremoved before drilling). The dust samples are collected at a range ofdifferent depths, eg. 0-10 mm, 10-25 mm, 25-50 mm and so on to determinehow the chloride content changes with depth from the surface. It also helpsto establish whether the chloride was present in the concrete when it wascast, or whether it penetrated the concrete from the surroundings. (See Fig.15.2).

The concrete samples are treated with acid to dissolve the cement and the chloridecontent is determined by titration against silver nitrate.

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16.3. Other detection methods

Listed below are additional tests that require special equipment and significant skillsand experience to obtain usable results. Such testing methods would have to beundertaken by specialist personnel skilled in the field of diagnostic testing.

Half-cell potential measurements to assess corrosive activity in concrete andthe probability of corrosion in steel reinforcement.

Ultrasonic pulse velocity measurements to locate areas of delaminations andhoneycombed concrete.

Electrical resistivity measurements to assess qualitatively the rate ofcorrosion.

Permeability tests to measure the water absorption of concrete.

In-situ compressive strength measurements using Schmidt Hammer.

Core sample testing for strength, permeability, contamination, compositionand density.

Measuring deflection of structural members under known applied loads.

17. Repair materials

17.1. Introduction

No matter how carefully a repair procedure is carried out, using the wrong materialwill most likely lead to early repair failure. Therefore, selection of appropriatematerials is an absolute requirement for obtaining durable repairs.

The basic criterion for selecting a repair material is that its material properties matchthe properties of the base concrete and a good bond is achieved and maintained atthe repair interface.

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17.2. Material properties

17.2.1 Factors affecting repairs

The material properties that affect the quality of a repair are:

Dimensional stabilityBond failure between new and old concrete is usually caused by relatively largeshrinkage of the new concrete (or mortar) while the old concrete does not shrinkfurther. Therefore, the repair material must be either shrinkage free or else be ableto shrink without losing bond.

Coefficient of thermal expansionWhen a composite of two materials of widely varying thermal coefficients undergoesa significant temperature change, differences in volume changes can cause failureeither at the bond line or within the section of the lower strength. Therefore, whenmaking large or thick patches or when placing an overlay, it is important to use amaterial with a coefficient of thermal expansion similar to that of the concrete beingrepaired.

Modulus of elasticityThe modulus of elasticity of a material is a measure of its stiffness. High modulusmaterials do not deform under load as much as the low modulus materials.Consequently, when materials with widely differing moduli are in contact with eachother and subjected to a common load, the lower modulus material would tend toyield or bulge transferring the load to the stronger material that if overloaded maythen fracture. For this reason, a wall or section made of relatively flexible (lowmodulus) material should not be patched with a stiff (high modulus) material.

PermeabilityPermeability refers to the capability of a material to transmit liquids or vapours.Good quality concrete is relatively impermeable to liquids but freely transmitsvapours. If impermeable materials (such as epoxies) are used for large patches,overlays or coatings, moisture vapour that passes up through the base concrete canbe entrapped between the concrete and the topping. Entrapped moisture can causea failure either at the bond line or within the weaker of the two sections.

Impermeable materials should also generally be avoided in patching concrete thathas been damaged due to corrosion of reinforcing bars as it may accelerate the rateof corrosion.

For the above reasons, whenever possible cementitious materials should be usedfor repairing concrete structures due to their compatible physical properties with theparent concrete. Cementitious mortars and concretes may be modified by theaddition of polymers but are always preferable to resin mortars if circumstancesmake it practical to use them.

17.3. Types of Repairs

17.3.1 General

A large variety of materials are used in the repair of concrete structures. Thesematerials may be used singly or in combination to achieve the best results accordingto the circumstances of a particular repair job. It is therefore essential to know the

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characteristics and application requirements of different materials so that anappropriate selection can be made for the repair in hand.

The materials commonly used for concrete repairs are:

Polymers (synthetic latexes) and polymer modified cement mortars andconcretes.

Synthetic resins and resin based material.

Unmodified cement based mortars and concretes.

Steel reinforcement coatings.

Substrate bonding coats.

Acrylic concretes.

Non-shrink hydraulic cement mortars.

Sprayed concrete.

Protective coatings.

Flexible joint sealants.

17.3.2 Polymers (synthetic latexes) and polymer modified cement mortars andconcretes

Synthetic latexes are made by dispersing polymer particles in water to form apolymer emulsion. When these emulsions are added to Portland cementconcrete/mortar, the spheres of polymer coalesce to form a film that coats theaggregate particles and hydrating cement grains and seals off the voids.

The polymer modified cementitious mortars and concretes are high performancerepair materials that work monolithically with parent concrete due to their similarphysical properties such as modulus of elasticity and coefficient of thermalexpansion. Their other good attributes are:

increased workability (therefore, less water-cement ratio),

excellent bond to existing concrete and steel in dry, damp or wet conditions,

low shrinkage,

high impermeability to water,

higher resistance to chloride ion and carbon dioxide penetration,

inherent alkalinity to passivate the steel reinforcement,

higher strength,

increased resistance to freeze-thaw damage and chemical attack,

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higher abrasion resistance.

The three basic polymers used as latex modifiers for concrete are:

polyvinyl acetates (PVA)

acrylics

styrene-butadiene rubber (SBR).

PVAs are not recommended for use in wet environments because some types mayhydrolyse and break down.

SBR latexes develop a brownish coat after being exposed to sunlight and this maymake them unsuitable for patching applications where colour matching is important.

16.3.2.1 Limitations

The working life of polymer modified mixes is relatively short. Therefore, thequantity of mix for a particular job should be limited according to the placing andfinishing time - about 20 minutes. If the mortar or concrete is manipulated afterthe latex has coalesced, cracking may occur on drying.

Application of polymers is also sensitive to temperature. At low temperatures thepolymer spheres will not coalesce to form a durable film around cement andaggregate particles. At high temperatures their working time is too short allowinglittle time to finish the repair. Manufacturers' instructions in this regard should becarefully followed.

16.3.2.2 Bonding coat

To obtain a high bond between the latex concrete overlay or mortar patch andthe base concrete, a bond coat is brushed or broomed onto the preparedconcrete surface. This bond coat can be the mixture used for the overlay orpatch, or made by mixing undiluted latex with Portland cement. The surface isfirst thoroughly wetted with clean water for not less than one hour prior toplacement. After removing all free water but with the surface still damp, sufficientmixed material to coat all bonding surfaces is then placed and vigorouslybroomed to assure maximum contact with the old concrete. The rate ofapplication of bonding material should be limited so that the bond coat does notdry before being covered with repair mortar or concrete.

16.3.2.3 Curing

The curing procedure of polymer modified concrete is different from normalconcrete. Wax or resin found in most curing compounds are incompatible withlatex and should not be used without prior evaluation.

The polymer film formed in polymer modified concrete helps to maintain highlevels of internal moisture in the concrete. Because of this, prolonged curing isneither necessary nor recommended. To prevent shrinkage cracking before thefilm has formed, however, all finishing operations must be completed and thesurface covered with a single layer of wet burlap as soon as the surface willsupport it. The curing cover is completed by placing a layer of polyethylene film

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over the wet burlap. This is left in place for 24 hours after that the burlap andpolyethylene are removed and the surface is permitted to dry for 3 to 5 days.

17.3.3 Synthetic resins and resin based materials

Epoxies are frequently used as repair materials because they bond well to almost allmaterials, cure rapidly, are high in both tensile and compressive strengths, exhibitgood chemical resistance, and they shrink very little during curing. Applicationsinclude use in bonding concrete (hardened to hardened, and hardened to fresh) andin patches, overlays and protective coatings.

However, there are significant differences between the physical properties of resinsand concrete. In particular, resins have an elastic modulus that is about one-tenththat of the concrete and coefficient of thermal expansion 5 to 8 times higher thanthat of concrete. The strength of resin based materials in compression is usuallyhigher than the strength of concrete, in tension it is much higher. These differencesresult in excessive stresses at the bond interface so that delamination of the epoxyrepair is likely to occur either at the interface or just within the concrete substrate.As a result, epoxy mortar repairs are more suitable for thin and small volumerepairs.

Further, in contrast to the cementitious materials that re-passivate the steelreinforcing bar, epoxy resin materials do not passivate the bar but rather arrestcorrosion only by excluding the oxygen due to their low permeability to moisture andgases. In fact, in marine environments epoxy repair materials are likely to trapchloride spray against reinforcement and introduce in-built potential chloride attackon the steel.

Epoxy resins offer excellent repairs in the following situations:

- Repairs of cracks up to 6 mm width by injection with low viscosity unfilledepoxy resin that has the potential to penetrate and seal cracks down to 0.02mm width. Crack injection is normally associated with dead cracks that arebasically inactive and do not move.

(If the cracks are live and continue to move with changing loads ortemperatures, they cannot be repaired with resins. In such cases, cracks aretreated as expansion joints and sealed with flexible materials).

- Bonding of new concrete to old concrete. Epoxy resin formulations provideexcellent adhesives and can give long drying times prior to placing of repairmaterials. This is particularly useful where complicated formwork has to beassembled.

- Bonding of steel, brick, concrete blocks and other materials to existingconcrete (i.e., use as adhesive).

- Epoxy resin grouts, mortar and concretes for reinstating deterioratedconcrete or patching in thin layer applications without problems of dryingshrinkage associated with cementitious repairs.

- Resin mixtures can be made fluid enough to flow into places by gravity sothat inaccessible places can be filled with them and compaction is

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unnecessary. This is valuable for packing bearings, machine bases and soon.

Epoxy compounds consist of a resin, a curing agent (hardener) and modifiers thatmake them suitable for specific end uses. Modifiers include accelerators that makethe rate of cure depend less on temperature, dilutents that reduce viscosity andimprove workability, and fillers such as sand and aggregate that lower cost,decrease shrinkage and reduce the volume change due to thermal expansion.

The resin generally consists of two components that are batched by volume andthoroughly mixed before the incorporation of aggregate. Chemical reactions start assoon as the resin components are combined and the working time will depend onthe system, the temperature and the handling procedure.

Accurate batching and proper mixing of the components is crucial for attainingmaximum strength and other properties of the epoxy materials. For this reason theyshould be mixed in whole batches that are obtained pre-proportioned from thesupplier.

If formwork is used with epoxy materials or epoxy modified concrete, the formsurfaces should be coated with a release agent compatible with the epoxy.

Surfaces of base concrete and steel should be primed with neat resin. Placementand consolidation should be done in layers of limited thickness as recommended bythe epoxy formulator.

Considerable skill and experience are needed for the successful application ofepoxy resin materials. They have to be applied within a very limited time before theyharden and have to be handled cleanly to avoid contamination of both the resinmixture and the people working with them. Therefore, it is advisable to employspecialists to supply them as well as apply them.

17.3.4 Unmodified cement based mortars and concretes

To match properties of the base concrete as closely as possible Portland cementmortar and concrete are frequently the best choices for the repair material.However, if there is a difference in aggregate source, maximum aggregate size orwater content, properties will differ. Also, the in-place concrete probably will haveundergone considerable drying shrinkage so that differential volume changesbetween a repair and the in-place concrete will almost certainly occur. Effects ofdifferential volume change can generally be minimised by maximising aggregatesize, minimising the water content and by following good curing procedures.

The concrete mix used for repairs must be capable of producing highly impermeableconcrete. Additives such as ground granulated blast furnace slag, pulverised fuelash or microsilica can be used in repair mixes to increase impermeability in thesame way as in new concrete. The use of accelerating admixtures may beadvantageous but the admixture itself should not contain more than 1 percentchloride ion by weight and the resulting total concrete should not contain more than0.1 percent chloride ion by weight of cement.

The nominal maximum size of the coarse aggregate should be less than of thepatch or overlay depth, but not more than 10 mm, bearing in mind that the concretemay have to get into fairly tight locations.

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The water-cement ratio should not exceed 0.4 by weight, lower ratios beingpreferred. Slump of mixes for shallow patches and overlays should not exceed 25mm. The slump of mixes that are to be consolidated around reinforcing steel byinternal vibration should not exceed 75 mm.

Accurately batched and properly mixed concrete is essential to the success ofrepairs. To avoid variability in site mixed concrete due to difficulty of accurateproportioning, pre-packaging at the maintenance shop or other suitable locationshould be considered. If the aggregate cannot be completely dried it must bepackaged separately from cement.

A number of proprietary pre-packaged cement based mortars and groutsincorporating special cements, chemical additives and admixtures, speciallyformulated to exhibit high bond, high strength and non-shrink properties are alsoavailable in the market. Prior to using any proprietary material its suitability for aparticular job must be verified from the manufacturer's printed literature.

Cement based unmodified materials do not always adhere successfully to oldconcrete and it is important that the old concrete be kept wet for a period of 12 to 24hours prior to repair to ensure that the old concrete does not suck away water fromthe new concrete thus preventing full hydration of the cement at the critical interface.However, prior to placing the new concrete the surface of the parent concrete mustbe dry and without free water so that the water-cement ratio at the interface is notincreased.

The other alternative is to prime the repair areas with Portland cement or latexmodified Portland cement grout or an epoxy system. A bonding agent must beapplied for low slump mixes.

The Portland cement grout should consist of a mixture of 1 part cement to ¾ or 1part fine aggregate and sufficient water to make a heavy cream consistency.

Polymer-modified bonding grouts have a short drying time (normally less than 30minutes) and cannot be used if there is much form fixing to be done before theconcrete can be cast.

Epoxy bonding coats have two special advantages. Firstly, they can be formulatedto have long open times, that makes them suitable for use in hot climates, or whenformwork has to be fixed after the bonding coat has been applied. Secondly, theymay provide a more effective barrier than cement grouts against the migration ofchlorides.

Note:Although they are water compatible, epoxy bonding coats are applied to a dry concretesurface. However, specially formulated resins are available for application to dampsurfaces also.

16.3.4.1 Curing

With low water-cement ratio repair concrete, a continuous water cure is thepreferred method for strength development.

Curing compounds may be used, however, they neither furnish desirable externalwater to low water-cement ratio mixes nor do they provide any cooling effect.They should not be used if additional material is to be later bonded to the surface

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being cured. Curing compounds should be applied at twice their usual rate toshotcrete and to other rough textured surfaces. It is essential that freshly placedsurfaces be kept moist until curing is initiated. A fog spray or a film should beused if there is to be any delay in application of curing compounds.

17.3.5 Steel reinforcement coatings

The purpose of using reinforcement primers and coatings is to ensure:

Adequate bond between steel and repair material.

Protection of steel in the repair zone against further corrosion.

Prevention of corrosion progressing under the primer.

The following types of coatings can be applied to steel reinforcement:

Cement slurry.

Cement slurry modified with polymer or latex emulsion.

Epoxy resin (with or without alkaline admixture).

Inhibitive primers (such as zinc chromate primer).

Zinc rich epoxy primers.

Alternatively, the cement paste from a well designed cementitious repair mix mayprotect the reinforcement better than any separately applied coating.

Caution:A coating is not an alternative to removing chloride contamination from the reinforcementnor will it prevent corrosion from being caused by chlorides that are already present on thereinforcement. It is therefore essential to remove the rust and chlorides from corrodedsteel before applying any primer.

Where the repair is cement based, coating of cement slurry (or the cement paste inthe repair mortar or concrete itself) would create a lasting alkaline environment onthe surface of the steel and offer a high degree of impermeability to water, carbondioxide and chloride ions.

Polymer modified cement slurries may dry too quickly to be effective in repairswhere forms have to be fixed after the coating is done, but they are suitable wherethe delay is short.

Use of epoxy resins, inhibitive primers and zinc rich primers should only be madeafter consultation with concrete repair experts, as in certain circumstances thesecoatings may do more harm than good.

Epoxy resin coatings act as an impermeable barrier against external moisture andgases, but if any chlorides are trapped under the coating the corrosion of steel couldstill continue.

Use of zinc rich paint: Where corrosion is due to a local flaw in generally soundconcrete, the grit blasted bar may be coated with zinc rich paint. Where there is

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generally poor quality concrete but the environmental attack is such that corrosionhas occurred in a limited area (i.e. there may be a large number of cathodescompared with the anodic corrosion sites), the anodic zinc coating may be rapidlyused up and steel re-attacked. In this case zinc rich paint should not be used.Where there is generally poor concrete and corrosion is very widespread (that is,there are many anodic as well as cathodic sites) zinc rich paint may be used.

17.3.6 Substrate bonding coats

Provided that the surface of the parent concrete has been properly roughened andall loose material removed, it is not essential to have a bonding layer. There is awidespread opinion that it is helpful, and whether one is used depends primarily onthe practicality of applying it.

Independent advice should be sought as to that product to use, remembering somebonding agents intended for use inside buildings actually break down eventually inthe presence of moisture. The practical difficulty lies in the requirement for theagent to be applied so that it is tacky at the time of placement of the repair material.The bonding coat will prevent bonding if it is allowed to become dry.

For epoxy materials the bonding coat consists of the same resin as used for therepair material.

For cementitious mortar and concrete, it is possible to use Portland cement grout,latex modified Portland cement grout or an epoxy system according to thepracticality of the situation. Detailed description of bonding coats has already beenincluded with relevant repair materials.

17.3.7 Acrylic concretes

Note: Description of this material is given as a matter of interest only. Its userequires training and special skills and repairs should best be entrusted toexperts.

Unlike normal Portland cement concrete, acrylic concrete contains no water and noPortland cement. It is made by mixing aggregates with acrylic monomers thatpolymerise during curing to form hard, tough concrete. Two types of monomers areavailable for making acrylic concrete: methyl methacrylate (MMA) and highmolecular weight methacrylate (HMWM).

Acrylic concrete is expensive, so obviously it cannot be used everywhere. However,because it develops compressive strength of 35 MPa to 70 MPa in 1 to 2 hours, ithas been used to repair pavements, bridge decks, parking decks and warehouseand factory floors that cannot be closed to traffic for several hours or days.

Acrylic concrete has few voids making it dense and impermeable. It resists intrusionof water, chlorides and most other corrosive chemicals. It develops high bondstrength with Portland cement concrete. Therefore, it is often used as an overlay,6mm to 50mm thick, on top of Portland cement concrete. A primer of catalysedacrylic monomer is usually brushed on the base concrete first.

Because of its low viscosity, the acrylic penetrates into the pores of Portland cementconcrete to produce a mechanical bond with the substrate.

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The aggregate for making acrylic concrete should be bone dry, with a maximummoisture content of 0.5 percent. Normally, these products are sold as pre-packagedsystems and manufacturer's instructions should be followed for mixing andapplication.

Both methyl methacrylate (MMA) and high molecular weight methacrylate (HMWM)gain strength in a matter of hours, but they are different in a few important ways.MMA has a low flash point, therefore, it is easily flammable, produces a non-toxicbut disagreeable odour, and has a short pot life. HMWM, on the other hand, has ahigh flash point and its odour is not strong. HMWM is easier and safer to use thanMMA but it also costs significantly more.

Because of its low viscosity, low volatility and relatively good bond strength, HMWMhas been used without aggregate to weld together inactive cracks in Portlandcement concrete. After mixing with a catalyst HMWM is poured onto the concretesurface and distributed with a squeegee. Material must be applied within 15minutes after mixing. If cracks are blown clean and dry beforehand, the monomercan penetrate the full depth of the cracks. However, monomers should not be usedto repair active cracks.

Caution:Personnel handling and mixing monomers should use eye-protection andimpervious gloves and aprons; respirators with chemical filters should be availablefor those who wish to use them. Mixing of monomers should be carried out in ashaded, well-ventilated area, free of ignition sources. Storage and handling of allmaterials must be done in accordance with manufacturer's recommendations.

17.3.8 Non-shrink hydraulic cement mortars

A number of proprietary Portland cement based products are available as non-shrink repair materials. Most of these products contain components that cause themortar or concrete to expand after it has hardened. The expansion is intended toovercome or compensate for the expected drying shrinkage and to maintain a tightbond to the material with that it is in contact. Then, when it undergoes subsequentdrying, the loss of moisture simply relieves the compressive stress instead ofcausing shrinkage.

Non-shrink cement mortars and grouts can be used in the following applications:

Repairing honeycombing, shrinkage cracks and spalls

Filling holes left by tie wires

Making watertight seals around penetrations

Stopping leaks

Patching precast concrete

Providing mortar beds under bearings and base plates

Anchoring bolts, dowels and rods.

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It is best to purchase the non-shrink mortar in standard packages rather than in bulk.Proportioning with standard packages is simple: all the user needs to do is mix thepackage contents with the recommended amount of water and aggregates.

17.3.9 Protective coatings

Surface coatings are used on concrete structures to provide additional protectionagainst ingress of water, water soluble salts and atmospheric gases. In addition,they enhance the aesthetic appearance and help in hiding the patchy appearance ofconcrete that has been repaired in different places.

It should be noted however that when concrete is already showing signs ofdeterioration and tests show that enough salt is present at the reinforcement tomake it rust, adding a protective coating will not help in reducing such deterioration.In such circumstances it is essential that the concrete be repaired first, and then, ifthe environment warrants, protected against further deterioration by application ofsuitable surface treatment.

For whatever reason the coatings are applied it must be accepted that they will notlast as long as a durable concrete surface and re-coating will be needed from timeto time.

Basically, there are two types of protective coatings:

1. Film forming - relying on adhesion to concrete.

2. Non-film forming - that penetrate into the concrete surface.

Film forming coatings are made from:

polyurethane resins

epoxy resins

coal tar epoxy

chlorinated rubber

acrylics

bituminous materials

polymer modified cement

Penetration type coatings are formulated with Silane/Siloxane.

Generally, film-forming coatings are highly efficient against ingress of moisture,water soluble salts (chlorides) and gases and vapours (carbon dioxide). However,build up of water vapour pressure behind them especially if water can get into theconcrete from another face can cause the coating to blister and peel off unless theadhesion of the film to concrete is very good. Also, if the film lacks elasticity andfails to bridge across active cracks or subsequently formed shrinkage cracks,pollutants will find easy ingress into the concrete at the site of cracked coating andwill eventually cause deterioration in concrete.

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Film forming coatings require significant amount of surface preparation. The surfaceof concrete must be free of oils, grease, loose surface layers, dust and surfacedefects such as blow holes and shrinkage cracks. The surface is either sand-blasted or grit/water blasted and steam cleaned and imperfections filled with suitablelevelling or fairing coats prior to the application of the coating system. Mostproprietary coating systems consist of a separate primer that improves the adhesionof the coating to the concrete and resists peeling or blistering. Also, pigmentedcoatings give much better protection and are more durable than unpigmentedcoatings.

Protective coating systems based on silane/siloxane are penetrating type sealersthat impregnate concrete and react with the moisture and silicates present in thecement thus modifying the concrete surface to form a water repellant but vapourpermeable barrier. Silane/Siloxane coatings, therefore, prevent contaminationagainst water soluble chlorides but being vapour permeable are not effective againstcarbonation.

Penetration type coatings require less surface preparation. However, a dry concretesurface is essential for successful application. They generally impregnate the outer2 to 5mm of the concrete surface and effectively seal blow holes, cracks up to0.3mm and other minor irregularities.

All proprietary coatings perform differently from each other in regard to ease ofapplication, adhesion to concrete, resistance against ingress of moisture, solublesalts and gases, durability, ability to stretch and bridge cracks and othercharacteristics. Their selection therefore should be made with care according to therequirements of the repair job in hand.

17.3.10 Sprayed concrete

(Source: Concrete Institute of Australia, Recommended Practice Sprayed Concrete,1987)

Note: Sprayed Concrete is a specialised work that requires skilled operators. Onlyan engineer with the knowledge of, and experience with, the material shoulddecide where and how it should be used.

Sprayed concrete consists of a mixture of cement, aggregate and water (it may alsocontain fibres and/or other admixtures) forcefully projected onto a surface through ahose and nozzle by means of compressed air.

Sprayed concrete develops excellent bond, is homogeneous and compact and doesnot sag in wall and overhead applications. It is thus suited to a wide range of coatingand lining operations.

There are two different techniques for applying sprayed concrete:

Dry-mix process

In the dry-mix process cement and aggregate are mixed together and metered into aregulated high-pressure hose. The compressed air carries the mixture to a specialnozzle equipped with a controlled water spray that dampens the mixture anddispenses it on to the receiving surface. The volume of the water added is controlledby the nozzle operator.

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Wet-mix process

In the wet-mix process a mixture of cement and aggregate mixed with water ismetered into the delivery hose and conveyed towards the nozzle where compressedair is injected that then projects the mixture into place.

Concrete sprayed by wet process has lower impact velocity than with the dryprocess because of inertia. Moreover, the extra workability required for pumping wetconcrete dictates the use of higher water content. Strict control is required in thewet-mix process to ensure pumpable concrete at all times, otherwise if the deliveryhose is blocked spraying has to be disrupted till the pipes can be cleared.

In the dry-mix process the quality of mix delivered on the surface relies heavily onthe operator's competence as the rate at that water is added has to be controlledmanually. But with a skilled operator it does give better control and adjustment andthereby better quality. Dry-mix process is often the preferred technique.

In addition to suitability, the economics of the use of sprayed concrete must also beconsidered. For some applications, sprayed concrete may be more economicalthan conventional in-situ concrete because it needs little or no formwork nor anycompaction, and the equipment for placing and mixing is small, portable type.

16.3.10.1 Limitations

Sprayed concrete also has some limitations that should be kept in mind. Theseare:

The finished product is largely dependent on the operator skill. Qualitycontrol, supervision and testing are difficult.

Correct batching of powdered admixtures in dry-mix is very difficult.Some admixtures can be hazardous to handle also.

Sprayed concrete must be reinforced with small mesh, small diameterreinforcement (or fibre reinforcement added to the mix) to prevent dryingshrinkage.

Dust from the dry-mix process can be objectionable. Protection must beprovided for adjacent buildings, materials, trees and gardens.

Curing in sprayed concrete is more critical than in ordinary work becauseof the small thickness usually applied. If curing compounds are used,they should be applied at twice their usual rate.

Sprayed concrete may have shrinkage and thermal properties differentfrom the concrete it is being applied to. (To minimise the effect ofdifferential shrinkage and thermal expansion latex admixtures and/or latexbased coatings to substrate may be used, but keeping in mind the limitedworking time available with latex based products).

Sprayed concrete can have relatively high porosity and permeability.

Poor weather conditions such as wind, rain and cold can severely affectthe application of sprayed concrete.

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The overall thickness of horizontal and vertical work is virtually unlimited(though for practical and economic reasons it is kept to less than 200mm).However, overhead work is generally limited to about 80mm thickness inone day.

Except for thin sections, the cost per cubic metre is generally higher thanfor in-situ work.

Sprayed concrete is difficult to finish. It is probably best not to trowel orfloat it.

17.3.11 Flexible joint sealants

Flexible joint sealants are required in repairing live cracks that are subject tomovement due to applied loads, shrinkage and temperature. Such cracks cannot besealed with rigid repair materials, such as epoxies, as failure would occur either inthe repair material or a new crack will develop elsewhere in the concrete.

There are three types of sealants in general use. Their properties are given below:

Mastics

1. generally viscous liquids of non-drying oils or low melting asphalts

2. movement capability not exceeding 15%

3. sealant recess depth/width ratio up to 2:1

4. extrude at high ambient temperatures

Thermoplastics

5. include asphalts, rubber modified asphalts, pitches and coal tar

6. liquid or semi-viscous when heated

7. pouring temperatures are usually above 100o

C

8. sealant recess depth/width ratio of 1:1

9. movement capability up to 25%

10. susceptible to ultra violet light, lose elasticity

11. extrude at high ambient temperatures

Elastomers

1. polysulphides, epoxy polysulphides, polyurethanes, silicones and acrylics

2. one part or two part materials

3. superior to other sealants

4. excellent adhesion to concrete

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5. not susceptible to softening within normal range of ambient temperatures

6. higher movement capability: up to 50% to 100%

7. sealant recess depth/width up to 1:2

8. Choice of a sealant generally depends on the following factors:

9. Movement capability of the sealant

10. Resistance to environmental exposure (weather, ultra violetradiation, water penetration, chemicals, etc.)

11. Adhesive properties, curing rate and paintability

12. Service temperature range

13. Sealant width/depth ratio (modulus characteristics)

14. Trafficability

15. Applicability in horizontal and vertical situations.

A large number of proprietary sealants are available. Choice for any repairapplication should be made according to the particular requirements of the job.Manufacturer's printed instructions should be strictly followed.

17.4. Questions to consider before choosing a repair material

(Source: Concrete Construction October 1984)

Concrete repair materials can be formulated to provide a wide variety of properties.Because the properties affect performance of the repair, choosing the right productrequires careful study. Suppliers of repair materials can help repair contractorschoose the right product but they need to know the anticipated service conditionsand the conditions under that the product will be applied. If you have not told thesupplier the answers to the following questions, you probably have not told himenough about the repair conditions for him to help you choose the best repairmaterial.

17.4.1 Application conditions

How thick is the repair section?In thick sections, heat generated during curing of the repair material may build upand produce unacceptable thermal stresses. Some materials may shrink too muchwhen placed in thick layers and some materials will spall if placed in thin layers.Others can be feather edged. When aggregates are used as an inexpensive filler orextender, the maximum size of aggregate that can be used will be dictated by theminimum thickness of the repair.

Will the substrate be moist?Some polymer materials will not cure properly in the presence of moisture. Othersare moisture insensitive. Heat generated during initial curing of some repair

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materials may create steam in a moist environment and the steam may cause failureof the repair.

At what temperature will the repair material be placed?Portland cement hydration ceases at or near freezing temperatures and cement

modifier emulsions won't coalesce to form films at temperatures below about 5o

C.Other repair materials can be used at temperatures well below freezing, althoughsetting time may be increased. High temperatures will make many repair materialsset faster, decreasing the working life or precluding their use entirely.

Will repairs be carried out in poorly ventilated areas or in areas where use offlammable materials is not permitted?Components of some repair materials are volatile and combustible. Odour can alsobe a problem.

Is the repair section on a vertical surface or on the underside of a horizontalmember?For unformed wall or soffit patches, repair materials must adhere to the substratewithout sagging.

16.4.2 Service conditions

How soon does the repair have to be put into service?If repairs are subject to early loading, rapid strength gain characteristics areessential.

Will the material be exposed to chemicals such as acids, sulphates, chloridesor strong solvents?Acids and sulphates will attack Portland cement-based materials, and chlorides maycause corrosion of reinforcing steel. Strong solvents may soften some materials.

Will the repair bear heavy traffic?Perhaps a material with good abrasion resistance and good skid resistance isnecessary.

Must the material bond to steel as well as to the concrete substrate?

What are the maximum and minimum temperatures that the material will besubjected to in service?Because thermal movements can cause stresses in the repair material or at thebond line, the range of service temperatures must be considered.

Will the finished repair be exposed to vibration?For applications such as machinery pedestals, vibration can cause distress in brittlerepair materials.

Is appearance of the repair important?If colour matching or duplication of original concrete texture is needed, many repairmaterials will be unsuitable.

How long must the repair last?If the repair is only temporary, perhaps a lower cost, less durable, or more easilyapplied material can be used.

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18. Repair options

18.1. Establish need for repairs

Before proceeding with the repairs an evaluation should be made to determine theneed for repairs. Repairs may be required for any of the following reasons:

Strength, stiffness and durabilityDamage needs to be repaired if it reduces the strength, stiffness or durability of thestructure to an unacceptable level. For example impact damage to beams andcolumns or loss of reinforcement by corrosion. In such cases calculations should becarried out to determine the stress levels and deformations in the damagedelements to assess the severity of damage and urgency for repairs.

AppearanceRepairs may be required to improve the appearance of the concrete surface, forexample some types of cracks, minor spalls, scaling, efflorescence, impact damage,etc. These defects may not immediately affect the strength of the structure but if leftuntreated could lead to further deterioration.

Functional performanceRepairs required if the function of the structure is impaired even if the strength,stiffness or appearance are not significantly affected. Examples: broken treads andhandrails on stairs, loss of sealants from expansion joints, dampness due to pondingof water, etc.

Prevention of further deteriorationSome repairs need to be undertaken to prevent the existing minor deteriorationgrowing worse if left unattended. For example: evidence of chloride penetrationwithout corrosion may require coating the concrete surface with silane to limit furtherchloride ingress.

18.2. Repair options

Depending on the nature of damage, urgency of repairs and availability of funds andresources, one of the following options may be adopted:

1. Do nothing other than carry out regular safety inspections. Wait and see.

2. Take action to prevent the deterioration from getting worse.

3. Carry out repairs to restore deteriorating parts of the structure to asatisfactory condition.

4. Demolish and re-build all or part of the structure.

18.3. Selection of repair methods

Having determined the repair option, it then remains to select an appropriate repairmethod for the job in hand.

Selection of the repair method depends on the location, type and extent ofdeterioration and the cause thereof. For a particular defect there may be one or

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more possible repair solutions. Therefore, a comprehensive knowledge of repairmethods and procedures is essential. These are given in the next Section.

19. Introduction to concrete repair procedures

19.1. General

This chapter presents methods for repairing common types of defects and damageto concrete structures. Techniques that require special equipment and expertisesuch as cathodic protection, chloride removal, re-alkalisation have been excluded.However, it should be noted that the conventional repair procedures for dealing withthe effects of reinforcement corrosion may be limited in their effectiveness. To haveany chance of success, rigorous adherence to the following procedures is essentialand patch repairs may extend well beyond the area of the initial damage. Even so,fresh electrolytic cells leading to immediate resumption of corrosion may occur atthe boundaries of the repair and the repair may have a very short life. Therefore,where damage is due to reinforcement corrosion, expert advice should be soughtwith a view to determining if more specialised techniques will be more cost-effective.

19.2. Repair methods

Chapters 20 to 26 cover the following repair methods:

1. Repairing cracks2. Patch repairs3. Recasting with concrete4. Repairs for corrosion5. Sprayed concrete6. Protective coatings

19.3. Sub-procedures

The procedures listed below are preparatory items of work generally required to becarried out prior to actual repairs. Some of them are common to different methodsof repairs and are referred to as "sub-procedures" in the Repair Methods.

1. Removing damaged concrete2. Removing concrete at joints3. Cleaning concrete substrate for patch repairs and re-casting4. Cleaning concrete surface for overlays5. Cleaning reinforcement6. Adding reinforcement7. Applying bonding coat to concrete8. Coating reinforcement9. Formwork for re-casting concrete10. Curing11. Surface preparation for external coatings.

The sub-procedures are described in Chapter 19.

19.4. Steps in repair work

1. Carry out detailed damage survey. Indicate location, extent, severity andparticulars of the damage.

2. Investigate the cause of damage or deterioration by conducting field and

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laboratory tests as necessary. If corrosion is present establish the cause.(Alternatively, determine if it is necessary to engage services of specialistconsultants to carry out the investigation).

3. Assess the strength and stability of the damaged structure.4. Establish the urgency of repairs.5. Examine alternative repair options, materials and methods.6. Assess if the repair work would require track closure, power outage, people

and traffic control, flagmen, assistance from police and utility authorities,falsework, temporary structures and health, safety and environmentalprotection measures.

7. Estimate the cost of repairs. Obtain competitive quotations/ tenders ifnecessary.

8. Prepare a project repair report on basis of the above. Recommend if therepair work be done by day labour, contract or through specialist agencies.

9. Organise the repairs.

20. Sub-procedures

20.1. Removing damaged concrete (sub-procedure)

20.1.1 Engineering discussion

Removal of damaged or deteriorated concrete may be necessary in severalsituations, such as:

Corrosion of reinforcement leading to cracking, spalling and delamination ofconcrete.

Impact damage causing cracks and spalls. Construction defects resulting in honeycombing, cracks and scaling. efective joints causing corrosion to reinforcement, cracking of concrete and

leaking. Repair of broken up old repairs.

Regardless of type of deterioration, all unsound and disintegrated concrete must beremoved.

Where reinforcement corrosion is the cause of the problem, obviously concrete mustbe removed to a depth that includes all the affected reinforcement and leaves someroom behind it as well, so as to give an adequate thickness of cover to steel in everydirection. If the new concrete is dense and of high quality this should inhibit the rateof new carbonation.

Where chloride contamination is the problem, there are more points to consider. Ifthe contamination comes from the original mix, limited concrete removal will not givecomplete protection to steel. In this situation coating the reinforcement with epoxyresins may be considered but advice should be sought on the risk of rapid corrosionwhere the coating terminates . But if the chloride contamination has come from asalty environment, the depth to which the concrete has been contaminated shouldbe determined by testing. The concrete cover should then be removed to a depthwhere chloride contamination is less than 0.1% of cement. If the salty environmentis aggressive, coating the finished concrete surface after the repairs should also beconsidered.

The extent of concrete removal depends on the extent of damage. It may belocalised or widespread. If the damage is due to severe but local corrosion in

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reinforcement requiring addition of bars, it may be sufficient to remove only thedamaged area of concrete plus the length needed to bond the new reinforcement.Concrete may be removed by power tools or by water blasting with or withoutentrained abrasives. If abrasive is entrained in the water jet, it also removes most ofthe rust from the exposed reinforcement.

If concrete is broken out from inside a large area of generally sound concrete, theedges of the area to be repaired should be cut with a perpendicular saw cut at least15mm deep to avoid a feathered edge finish. The feathered edges of repairedconcrete will easily prise off as a result of changes in stress. The face of the sawcut must be roughened slightly (eg. with a needle gun) to help the repair material tobond with it. (See Figs. 19.1a and 19.1b).

In situations of soffit repairs to beams and slabs, profile of removed concrete shouldbe planned to allow escape of air during re-casting. Vent holes may be drilledthrough the slab for the same purpose.

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20.1.2 Procedure

1. Before removing any concrete from a load bearing structure considercarefully whether the concrete to be removed is providing essential supportfor the structure. If yes, support the structure first.

2. Ascertain the area of damaged concrete to be removed and repaired.Consider extending the repair area to some line where the boundary of thenew work will fit in with a feature of the structure.

3. Mark the repair area with horizontal and vertical lines. Avoid sharp acuteangles and re-entrant corners.

4. Make perpendicular saw cuts along the lines. Depth of saw cut should beminimum 15mm, maximum 20mm. Take care not to cut throughreinforcement bars. For small areas and where saw cutting is not practical,use chipping tools to remove concrete but ensure that edges of repair areaare cut perpendicular to the surface.

5. Remove the damaged concrete within the saw cut boundaries to the depthrequired using power tools and/or high pressure water blasting. If removalof material has exposed more than half of the perimeter of reinforcing bars,remove the concrete further to expose the bars completely with minimum20mm clearance behind the bars to ensure encasement and bond.

Exposure of steel reinforcement must also continue along its length untilnon-corroded steel is reached and continued at least 50mm beyond toshow sound rust-free metal.

Corners of the removed concrete at the substrate level should be roundedto obtain good contact between the substrate and patch material.

6. Roughen the edges of saw cuts with needle guns.

7. Ensure that all weak and flaky concrete is removed throughout thesubstrate.

20.2. Removing concrete at joints (Sub-procedure)

20.2.1 Engineering discussion

Three types of joints are provided in reinforced concrete structures:

Construction joints Contraction joints Expansion joints

At construction joints the structure is intended to remain monolithic withoutmovement across the joint.

Expansion and contraction joints, however, are provided to allow movement in thestructure due to shrinkage, creep and thermal effects.

Depending upon the joint detail, a joint may incorporate continuous reinforcementacross it (or, the reinforcement may be stopped on either side of it), dowel bars for

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shear transfer and water stops and sealants to prevent water penetration. Becauseof the complexity of detail at the joints, they are difficult to construct and theconcrete at a joint may become porous and honeycombed due to lack ofcompaction. Therefore, it is not surprising that many joints fail resulting in crackingof concrete, corrosion of reinforcement and water penetration.

Construction joints that open and behave as unintended movement joints must bewidened and sealed at the external face as soon as they are noticed and beforecontamination can occur. (Refer methods for repairing cracks).

A badly deteriorated joint must be repaired by removing the affected concrete andreconstructing the joint.

Removing the concrete 'cover' at a joint is often a matter of removing concrete bothon the external surface and the internal joint face and it usually results in removingall the concrete in the immediate vicinity of the joint. The reinforcement, however,must be left in place so that the re-cast concrete can be tied in to the existingconcrete.

If the joint incorporates dowel bars, it is often necessary to remove the dowelassembly completely. This means that all the concrete may have to be removed asfar as 500mm on either side of the joint.

Repairing dowelled joints that allow movement by removing the concrete on oneside only seldom succeeds, because often it is the lack of accurate alignment of thedowels that causes distress in the joint by not permitting free sliding of the concretemember. In such cases the dowel bars must also be removed and replaced by pre-assembled dowels that are set parallel to each other and in one plane and installedaccurately in formwork perpendicular to the joint plane before concrete is cast.

20.2.2 Procedure

1. If necessary, support the structure on both sides of the joint before anyconcrete is removed.

2. Ascertain the area of damaged concrete to be removed.3. Mark the repair area with lines running parallel and perpendicular to the

joint.4. Make perpendicular saw cuts 15 to 20mm deep along the lines. Take care

not to cut through reinforcement bars.5. Remove the damaged concrete between the saw cut and joint to the depth

required.6. If the concrete requires removal through full depth of a slab, the slab should

be cut below the saw cut at an angle of approximately 20o

to the vertical,sloping towards the joint. To achieve a neat joint on the soffit of the slab,consider making a saw cut on the soffit also offset from the saw cut at thetop of slab to give a sloping construction joint. (See Fig. 19.2).

7. Roughen the edges of saw cut with needle guns.8. Ensure that all weak and flaky concrete is removed.

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20.3. Cleaning concrete substrate for patch repairs and re-casting (sub-procedure)

20.3.1 Engineering Discussion

To ensure good adhesion of mortar or new concrete to the parent material, thesubstrate should be clean and free of dust and loose material.

20.3.2 Procedure

1. After removal of damaged concrete, remove loose particles and dust withhigh pressure water or vacuum cleaning. Air blowing may be effective, butthe compressor should be equipped with a functioning oil trap to preventcontamination of concrete by oil.

2. Do final cleaning immediately before placement of repair material to ensurethat all contamination is eliminated.

All concrete surfaces on that new ovrelays are to be bonded must be cleaned of dirt,oil, grease, asphalt, tar, laitance and deteriorated concrete. Ashpalt or oil particularlyinterfere with methyl methacrylate polymerisation and therefore must be removedthoroughly. Detergents may remove suface oil contamination, however, oils thathave penetrated the surface should be removed by chipping or scarification.

20.4. Cleaning Concrete Surface for Overlays

20.4.1 Engineering Discussion

All concrete surfaces on that new overlays are to be bonded must be cleaned of dirt,oil, grease, asphalt, tar, laitance and deteriorated concrete. Asphalt or oilparticularly interfere with methyl methacrylate polymerisation and therefore must beremoved thoroughly. Detergents may remove surface oil contamination, however,oils that have penetrated the surface should be removed by chipping or scarification.

20.4.2 Procedure

1. Remove tar and asphalt by mechanical means followed by sandblasting.2. Remove all traces of dirt, oil and grease by scrubbing with a proprietary

alkaline detergent solution such as sodium metasilicate or trisodiumphosphate. Wash with plenty of water to ensure complete removal of thedetergent. Dirt alone may be removed by water blasting, with wire brushesor similar mechanical means.

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3. If oil has penetrated into surface, remove affected concrete by chipping orscarifying followed by water or sand blasting to remove loose material.

4. Remove laitance and deteriorated concrete by water or sand blasting.5. Immediately prior to application of overlay material, blow the concrete

surface with clean, dry and oil free compressed air to ensure completeremoval of all dust and loose particles.

20.5. Cleaning reinforcement (Sub-procedure)

20.5.1 Engineering discussion

If the deterioration of concrete has been caused by corrosion of reinforcement, theproducts of corrosion must be removed before placing the new concrete, otherwisethe repair will not be effective. If the damage is due to chloride contamination, it isessential to remove all rust from the steel, as any residual rust will be contaminatedwith chlorides that could restart the corrosion later.

Water-abrasive blasting is the most effective method for cleaning the reinforcement.The abrasion removes the solid rust and water dissolves the chlorides away.Enough concrete must be cut away on the blind side of the reinforcement to allowroom for water-abrasive blasting - the space will be needed for providing concretecover to steel anyway.

If the cause of damage is carbonation, rust removal is less critical and it will besufficient to remove any loose rust that might prevent adhesion of repair material tosteel.

20.5.2 Procedure

1. Ascertain from test results if chloride contamination has occurred.2. Inspect the reinforcement after the concrete has been removed.3. If deterioration is due to chloride contamination or if the reinforcement is

covered with loose corrosion products and has developed pits, use water-abrasive blasting till all the rust is removed and steel has achieved Class2½ "Near White" surface cleaning to AS1627.4.

4. If there is no chloride contamination and the rust is slight and adheres fastto steel, without signs of loose scales and pitting, clean the reinforcementby water blasting only to remove any loose material.

20.6. Adding reinforcement (Sub-procedure)

20.6.1 Engineering discussion

If rusting has reduced the cross-sectional area of reinforcement by more than 15%,extra reinforcement must be added before the repair is made good to restore thecross-sectional area to its original value.

20.6.2 Procedure

- Inspect the exposed reinforcement for damage after the concrete coverhas been removed.

- Examine if corrosion has reduced the cross-sectional area of any bars bymore than 15%. If yes, measure the length over that such corrosionextends.

- The length of lapping bar required = corroded length + 2 x splice lengthrequired by AS3600.

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- Lapping bars shall be of the same diameter as the existing bars.- Ensure that sufficient concrete is removed to accommodate the lapping

bars (See Fig. 19.3).- Clean concrete and existing reinforcement as per sub-procedure 19.3 and

19.5.- Attach the lapping bars to existing bars with tie wires or by welding.

Ensure that lapping bars will have adequate concrete cover all around. Ifwelds are used remove all weld slag and splatter from steel and concrete.

20.7. Applying bonding coat to concrete (Sub-procedure)

20.7.1 Engineering discussion

Engineering aspects of bonding coats have been discussed in Chapter 16 "RepairMaterials".

If the selected repair method requires application of a proprietary bonding coat toconcrete substrate, it is essential first to read the manufacturer's instructions forpreparation and application of the particular bonding material. These must bestrictly followed. Directions given here are for general guidance only.

Working time of different types of bonding coats varies and is often limited.

The bonding coat will prevent bonding if it is allowed to dry. It is therefore importantto plan beforehand the timing for its application so that the repair can be completedwithin the allowed working period.

"Wetness" of concrete substrate required prior to application of bonding coats is alsodifferent for different bonding materials. Generally, epoxy bonding coats are appliedto dry surfaces, but specially formulated resins are available for damp surfaces also.Cementitious bonding coats (whether modified with latex or unmodified) require thesubstrate to be "pre-wetted" but only just damp at the time of application.

20.7.2 Procedure

Clean the concrete surface as per sub-procedures 19.3 and 19.4 and steelreinforcement as per sub-procedure 19.5.

For applying unmodified cementitious bonding coat, eg. Portland cementgrout, (or repair mortar or concrete), keep the concrete surface wet for 12 to24 hours prior to starting repair.

For applying latex modified Portland cement bonding coat (or repair mortaror concrete), keep the concrete surface wet for at least one hour.

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Remove all free water and allow the surface to dry until it is just damp.

Apply the bonding coat material with a brush or broom working it vigorouslyinto the substrate.

For applying epoxy based bonding coats, allow the substrate to drycompletely (unless the epoxy is formulated for application on damp surface).

Apply the bonding coat material with a brush or broom working it vigorouslyinto the substrate. Cover only as much area of the substrate as can berepaired or overlaid with repair mortar or concrete within the working time ofthe bonding material.

Apply the bonding material progressively as the repair work advances.

20.8. Coating reinforcement (Sub-procedure)

20.8.1 Engineering discussion

Engineering aspect of coating steel reinforcement has been discussed in Chapter 16"Repair Materials".

Apart from cement slurry, other coatings are generally proprietary products and it isessential to read the manufacturer's instructions for their application. These mustbe strictly followed.

20.8.2 Procedure

- Clean the steel reinforcement as per sub-procedure 19.5.- If required, add lapping reinforcement as per sub-procedure- Apply the selected bonding coat to steel bars with a brush working vigorously

to ensure that bars are evenly covered all around.- Remember, working time of bonding coats is limited. Therefore, follow

immediately with the repair material.

20.9. Formwork for re-casting concrete (Sub-procedure)

20.9.1 Engineering discussion

Where deteriorated concrete in structural elements is to be replaced, it must be re-cast using appropriate formwork. Often the space for re-casting concrete is verylimited, necessitating the use of super-plasticised or pumped concrete andcompacting with external vibrators.

Formwork for re-casting repairs must be very rigid and well-supported to prevent thenew concrete from sagging away from the old concrete under its own weight, towithstand pumping forces if concrete is to be pumped into forms and to withstandthe forces of clamped-on external vibrators.

Heavy gauge steel forms are preferable because as well as being rigid they allowquicker dissipation of heat of hydration of the fresh concrete thus reducing thecontraction stresses. Formwork should be provided with birdmouth hoppers andopenings where appropriate for feeding new concrete and inserting poker vibrators.(See Fig. 19.4). Form releasing agents used should be compatible with the repairmaterials, particularly epoxy based and latex modified concretes and grouts.

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20.9.2 Procedure

1. Pre-assemble the formwork. Use appropriate form release agent to suit therepair material to be placed.

2. Fix the formwork and its supports immediately after applying bonding coatsto concrete substrate and reinforcement.

3. Make the forms mortar tight by sealing with building tape or sealants alongall joints.

4. Clean the forms of all the debris before placing any concrete.

5. Place re-casting concrete within the working time of bonding coats if used.

6. Ensure good compaction of concrete using pokers and external vibrators.

20.10. Curing (Sub-procedure)

20.10.1 Engineering discussion

All types of cementitious repair need thorough and continuous curing to developstrength and impermeability and to reduce drying shrinkage to a minimum whilebond strength is developing.

Water used for curing shall be free from ingredients harmful to concrete.

Curing procedures for polymer modified and unmodified cementitious materials aredifferent and have been discussed at length under "Repair Materials". Epoxy basedmaterials are self-curing and do not require external curing.

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Curing compounds should not be used with latex modified concretes as the wax orresin in most curing compounds is incompatible with latex.

Curing compounds should also not be used if additional material is to be bondedlater to the surface being cured.

Continuous water cure is always preferable to membrane cure. Curing membranesdo not provide any reserve of extra water to make up for any that escapes and arenot likely to provide enough curing in the critical early stages. Curing membranesapplied after the wet cure, however, can help to slow down drying.

20.10.2 Procedure for curing latex modified cementitious concretes andmortars

1. Complete all surface finishing operations as soon as possible (beforeformation of the polymer film). Protect freshly finished surface from rain ordamage from other causes.

2. As soon as the surface can support it and prior to formation of polymer film,cover the surface with a single layer of wet hessian. Place polyethylene filmover the wet hessian to prevent moisture loss by evaporation.

3. Remove polyethylene film and hessian after 24 hours. Allow the surface todry for 3 to 5 days.

20.10.3 Directions for curing unmodified cementitious concretes and mortars

1. Complete all finishing operations before the concrete or mortar starts setting.Protect freshly finished surface from rain or damage from other causes.

2. Keep concrete moist by light water spray immediately after initial set, untilcuring methods are in place.

3. Cover with saturated hessian sheets followed by polyethylene film to preventmoisture loss. Alternatively, the surface may be cured by continuousspraying or flooding with water.

Curing shall be continued for minimum 4 days in temperate weather and 7 days inhot, dry or windy conditions.

20.11. Surface preparation for external coatings (Sub-procedure)

20.11.1 Engineering discussion

Preparation of concrete surfaces is necessary to achieve bonding of film formingcoatings and penetration of penetration type coatings.

In new structures, this preparation may only require removal of oil or wax formrelease agents and curing compounds that could be sticking to concrete and preventadhesion of coatings.

In old structures, apart from repairing any deterioration, surfaces will need to becleaned of dirt, dust, oil, grease, old paint, moss and algae growth.

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The surface also needs to be reasonably dry for the coatings to stick properly andresist peeling and blistering. (However, for cementitious coatings the surfaces haveto be pre-soaked with water and should be just damp before application of coating).

Coating materials are available as proprietary products. Manufacturer's instructionsregarding surface preparation and application should be carefully studied andfollowed before undertaking any work.

20.11.2 Procedure

1. Clean the surfaces to be coated by suitable methods according to existingcondition of the structure. Use high pressure water jets, sandblasting (wet ordry), power operated wire brushes, grinding discs, etc to remove dirt,laitance, weak concrete, corrosion affected concrete and any otherdeterioration. Remove oil and grease with proprietary alkaline detergents,and moss and algae with fungicidal solutions, rinse off the solutions withlarge quantities of water.

2. Repair all deterioration in concrete such as cracks, spalls, reinforcementcorrosion, etc.

3. Fill surface irregularities, blow holes, tie-wire holes and the like with suitablefairing, levelling or sealing coats or mortars.

4. Allow the repairs to set and cure.

5. Allow the concrete to dry. (For cementitious coatings, however, pre-soak theconcrete with water for 24 hours. Remove free water and allow to dry till justdamp).

6. Immediately prior to application of primer or final protective coat, as required,remove any dust and loose particles with oil free compressed air.

21. Repairing cracks

21.1. Types of cracks

Description of various types of cracks that can occur in concrete structures has beengiven in Chapter 14.

For purposes of repair, however, there are two types of cracks:

1. Dead cracks - These are inactive cracks and do not move

2. Live cracks -These are subject to movement due to applied loads andtemperature changes.

21.2. Repair methods for cracks

Dead cracks can be repaired by any of the following methods:

Epoxy injection

Grouting

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Routing and sealing

Drilling and plugging

Stitching

Adding reinforcement

Overlays and surface treatments

Live cracks can be repaired by:

Flexible sealing.

21.3. Cracks that should be repaired

Not all cracks are structurally significant. The vast majority are caused by shrinkageor other tension stresses that develop as the structure supports itself and have noinfluence on strength or durability.

It is important to recognise if cracking is of a size and type that is harmful, and actaccordingly.

Generally, fine cracks up to 0.3mm width have no adverse effect whenreinforcement cover is adequate. Fine cracking will also heal autogenously as thefree cement is exposed to moisture. In this process calcium hydroxide in the cementreacts with carbon dioxide and moisture forming calcium carbonate and calciumhydroxide crystals that tend to seal the crack. Healing will not occur if the crack issubjected to movement or if there is flow of water through it.

Flexural cracks in a bending member do not normally progress beyond the neutralaxis and have a reduced width at the tensile reinforcement. In such cases a surfacecrack width of 0.5mm is usually acceptable. In members protected from driving rainand in absence of aggressive marine and industrial environment, even 1mm crackscan be tolerated.

Stable cracks of the size and type described are generally harmless and need notbe repaired.

Harmful cracks develop due to such factors as carbonation, chlorination, alkali-aggregate reaction, corrosion, overloading of structure, foundation movement,insufficient reinforcement and lack of adequate cover. It is important to identify thepresence of these causes. All harmful cracks must be repaired.

Longitudinal cracks expose long lengths of reinforcement to possible sources ofcontamination and they must always be regarded as potentially dangerous, even ifthey may not be already the result of rusting.

Cracks due to severe deterioration (as in corrosion and impact damage) thatnecessitate removal and replacement of concrete will require repair methods otherthan crack repairs.Transverse cracks may or may not be serious depending on their width, location andthe exposure conditions.

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21.4. Epoxy injection

Note: Epoxy injection of cracks in concrete is a highly skilled process; its successdepends largely on the experience of the operator. It is not a process thatshould be attempted by a general contractor. Information given below is,therefore, for general guidance only.

21.4.1 Engineering discussion

Epoxy injection is used to restore structural soundness of structures afflicted withinactive cracks. Cracks as narrow as .05mm can be bonded and sealed by injectingwith low viscosity epoxy. Cracks wider than 6mm generally require a mix of epoxyand mineral filler, or Portland cement grout. The technique generally involves drillingholes at close intervals along the cracks, fitting them with entry ports, then injectingthe epoxy under pressure.

Some cracks extending downwards from nearly horizontal surfaces may be filled bygravity if the width of crack is more than 0.5mm and depth is less than 300mm. Forthis, the top surface edges should be chipped or sawn to form a small trough toprovide an inlet for gravity flow of resin into the crack.

Except for certain specialised epoxies, the method cannot be used if the cracks areactively leaking. While moist cracks can be injected, water or other contaminants inthe crack will reduce the effectiveness of the epoxy repair.

21.4.2 Repair procedure

- Clean the cracks. Remove any contamination (such as oil, grease, dirt, fineparticles of concrete) from the cracks with water under high pressure, orsome specially effective solvent. Blow out the residual water or solvent in thecrack with filtered (dust and oil free) compressed air or allow adequate timefor air drying.

Note: The epoxy system used should be capable of bonding to wet surfacesunless it can be assured that the crack is dry.

- Seal cracks at the surface to keep the epoxy from leaking out before it hasgelled. The surface can be sealed by brushing an epoxy on the surface ofthe crack and allowing it to harden. If extremely high injection pressures areneeded, cut a 12mm deep x 20mm wide V-groove along the crack, fill with anepoxy and strike off flush with the surface.

- Drill holes into the crack for fitting pipe nipple entry ports for epoxy injection.A vacuum chuck and bit are useful in preventing the cracks from beingchoked with drill dust. Spacing of ports varies between 150mm to 500mmgenerally depending on the width and depth of the cracks. Establish the firstand last entry ports at or near the bottom and top, respectively, of anyvertical crack, or at the ends of any horizontal crack in a vertical or horizontalmember.

- Mix the epoxy. There are two methods for mixing epoxy, batch orcontinuous.

In batch mixing the adhesive components are mixed according to themanufacturer's instructions using a mechanical stirrer.

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Mix only the amount of adhesive that can be used prior tocommencement of gelling of the material.

In the continuous mixing system, the two adhesive components passthrough metering and driving pumps prior to passing through anautomatic mixing head. The continuous mixing system allows the useof fast setting adhesives that have a short working life.

- Inject the epoxy. Epoxy can be injected with hydraulic pumps, paint pressurepots or air-activated caulking guns. Select the injection pressure carefully.Increased pressure does not necessarily accelerate the rate of injection. Infact, excessive pressure can propagate the existing crack further.

If the crack is vertical, commence the injection of epoxy at the lowest entryport until the epoxy exudes from the next port above. Cap the lower port andrepeat the process at successively higher ports till the crack has beencompletely filled and all ports have been capped.

For horizontal cracks, carry out the injection from one end of the crack to theother in the same manner. The crack is full only if the pressure can bemaintained. If the pressure cannot be maintained, the epoxy is still flowinginto the crack or leaking out from somewhere.

- After the crack has been sealed, remove the projecting entry ports and fillholes with an epoxy patching compound. If required, remove or even out thesurface seals by grinding in order to restore the appearance of the structure.Apply surface coating if it is part of the repair process.

21.5. Grouting

21.5.1 Engineering discussion

Wide cracks that are inactive may be repaired by filling with Portland cement grout.Grout mixture may contain cement and water or cement plus sand and waterdepending on the width of the crack. Other admixtures or polymers may be used toimprove the properties of the grout, such as bond. The water-cement ratio shouldbe kept as low as practical to maximise strength and minimise shrinkage.

21.5.2 Repair procedure

1. If the surfaces in the crack are contaminated with oil or grease, remove thecontamination with detergents. If oil and grease have penetrated intoconcrete, remove the affected concrete and repair by replacing with freshconcrete.

2. Flush out all dust and debris from the crack with high pressure water jets.

3. Install grout nipples at intervals astride the crack.

4. Seal the crack between the nipples with a sealant.

5. Flush the crack to clean it and test the seal.

6. Grout the crack until it is completely filled. Maintain the grout pressure forseveral minutes to ensure good penetration.

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7. Remove the nipples and fill holes with cement mortar.

21.6. Routing and sealing

21.6.1 Engineering discussion

Routing and sealing is used for repairing dead cracks that are of no structuralsignificance. The method involves enlarging the crack along its exposed face andfilling it with a suitable joint sealant.

This is the simplest and most common technique for crack repair and can beexecuted with relatively untrained labour. It is suitable for both fine pattern cracksand larger isolated defects, but will not be effective on active cracks and crackssubject to a pronounced hydrostatic pressure.

The purpose of the sealant is to prevent water from reaching the reinforcing steel,development of hydrostatic pressure within the crack, staining of concrete surfaceand causing moisture problems on the far side of the crack.

The sealant material is often an epoxy compound. There are many commercialproducts and type and grade of sealant most suitable for the specific purpose andconditions of exposure should be selected.

21.6.2 Repair procedure

1. Prepare a minimum 6mm wide x 6mm deep V-groove at the surface alongthe crack using a concrete saw, hand tools or pneumatic tools. (See Fig.20.1).

2. Clean the groove with an oil free air jet. Allow to dry completely beforeplacing the sealant.

3. Apply the sealant as per manufacturer's instructions.

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21.7. Drilling and plugging

21.7.1 Engineering discussion

This method is most often used to repair vertical retaining walls and consists ofdrilling a hole down the length of the crack and grouting it to form a key. (See Fig.20.2). The crack must run reasonably straight and the hole must be large enough tointersect the crack along its full length and provide enough section of shear key tostructurally take the loads exerted on it. The grout key prevents transversemovement of the sections of concrete wall adjacent to the crack. It will also reduceheavy leakage through the crack and loss of soil from behind the wall.

If water tightness is also required in addition to the structural load transfer, a secondhole should be drilled and filled with a resilient material of low modulus, the first holebeing grouted.

The grout is made up of cement and sand (1:3) and water. The water-cement ratioshould be kept as low as practical to maximise strength and minimise shrinkage.Other admixtures or polymers may be added to improve the properties of the grout.

20.7.2 Repair procedure

1. Drill a 50mm to 75mm diameter hole centred on and following the crack.

2. Flush the hole and crack with high pressure water jet to remove dust anddebris. (Caution: Restrict flushing to the minimum so that backfill soil is notwashed into the crack). Allow the crack to damp dry.

3. Seal the crack tight on the exposed face. Allow the seal to cure and harden.

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4. Fill the hole and crack with grout.

21.8. Stitching

Note: Stitching may be used when tensile strength must be re-established acrossmajor cracks. Stitching also tends to increase stiffness in the structure thatmay cause cracking elsewhere. This method of repair should therefore beadopted only under advice of a structural engineer.

21.8.1 Engineering discussion

This method involves drilling holes on both sides of the crack and grouting institching dogs (u-shaped metal units with short legs) that span across the crack.(See Fig. 20.3.)

Where possible, stitching should be done on both sides of a concrete section so thatfurther movement of the structure would not pry or bend the dogs. This isparticularly so in tension members where the dogs must be placed symmetrically. Inbending members however the cracks may be stitched on the tension face only.

Stitching will not close a crack but can prevent it from propagating further. If it isrequired to seal the crack, the sealing should be completed before stitching begins.

21.8.2 Repair procedure

1. If it is required, seal the crack by epoxy injection, grouting, or routing andsealing.

2. The stitching dogs should be variable in length and orientation so that thetension across the crack is not transmitted to a single plane but welldistributed in the concrete.

3. Drill holes on both sides of the crack accordingly to suit the size and location

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of the stitching dogs. Spacing of the dogs should be reduced at each end ofthe crack.

4. Clean the holes of all dust and debris.

5. Anchor legs of the dogs in holes with a non-shrink grout or epoxy resin-based grout system.

21.9. Adding reinforcement

Note: Adding reinforcement to an existing structure to repair cracks should not beundertaken without advice of a structural engineer.

21.9.1 Engineering discussion

When cracks impair the strength of a concrete structure, the structure can bestrengthened by addition of conventional or prestressed reinforcement. The methodof fixing such reinforcement will depend on particular structure and type and locationof the cracks. The damage must be examined by a structural engineer andreinforcement designed to resist the forces causing the cracks.

21.9.2 Repair procedure with conventional reinforcement

Cracked structures may be repaired by epoxy injection and reinforcing bar insertionacross the cracks. (See Fig. 20.4.)

1. Clean the cracks of dust, debris and contamination. Allow the cracks to dry.

2. Seal the cracks at exposed surfaces with an epoxy sealant approximately3mm thick and 40mm wide. Allow one or two vent holes at the top for escapeof air during epoxy injection.

3. Drill 20mm diameter holes at 45o

to the concrete surface and crossing the

crack plane at approximately 90o

. Use vacuum bits and chucks to preventdust from clogging the cracks. The holes should extend minimum 450mm oneach side of the crack. Number, spacing and location of the holes should bedetermined by design, taking care to avoid existing reinforcement.

4. Fill the holes and cracks with epoxy pumped under low pressure (350 to550kPa). The epoxy used should have very low viscosity and high modulusof elasticity and it should be capable of bonding to concrete and steel inpresence of moisture. Holes should be filled with epoxy to part depthsufficient to raise the epoxy level to surface when steel bars are inserted.

5. Insert reinforcing bars (typically 12 or 16mm diameter) into the epoxy filledholes. Clean off any overflowing epoxy immediately.

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21.9.3 Repair procedure with external prestress steel

Post-tensioning is often used to strengthen a structure damaged by structuralcracking or when the cracks have to be closed. This technique uses prestressingstrands or bars to apply a compressive force to negate the tension causing thecracks. (See Fig. 20.5). It requires a thorough design of the prestressing force,detailing of the anchorage system and analysis of the secondary effects on thestructure. The task should therefore best be entrusted to a structural engineer.

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21.10. Surface treatments

21.10.1 Engineering discussion

Slabs with numerous fine cracks caused by drying shrinkage or other one-timeoccurrences can be effectively repaired by the use of protective coatings or surfacetreatments.

Concrete surfaces that are not subjected to wear may be sealed with a low solid,epoxy resin-based system (film forming type) or silane/siloxane based coatings(penetration type) depending on the circumstances of the repair job.

Surfaces subject to traffic such as walkways, parking decks and interior slabs maybe sealed with a heavy coat of epoxy resin covered with aggregate to provide skidresistance. The method will close dormant cracks, even if the aggregate is abradedfrom the surface, since traffic cannot abrade the resin that has penetrated thecracks.

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A suitable proprietary repair system should be selected according to therequirements of the job.

21.10.2 Repair procedure

1. Select appropriate repair materials according to the particular jobrequirements.

2. Clean the surface to remove laitance, or contaminants such as grease or oil.(Refer sub-procedure 19.11.)

3. Apply the repair materials strictly according to the supplier's writtenspecifications.

21.11. Flexible sealants for live cracks

21.11.1 Engineering discussion

Live cracks are treated as movement joints and repaired with flexible sealants.

The sealant is generally installed in a wide recess cut along the crack. Thedimensions of the recess (width and depth) depend on the total crack movementand the cyclic movement capability of the joint sealant used. The crack movementshould be calculated taking into account the applied loads, shrinkage andtemperature variations.

Where aesthetics is not important and surface is not subject to traffic, the sealantmay be applied on the surface without making a recess. (See repair proceduresbelow).

The commonly used sealants for movement type of joints are polysulphides, epoxypolysulphides, polyurethanes, silicones and acrylics. They have generally excellentadhesion to concrete, high movement capability of 50% to 100% and require awidth/depth ratio of 2:1.

21.11.2 Repair procedure for recessed seal

1. If the concrete is still uncontaminated, cut a recess along the line of the crackusing a power chisel, crack cutter or saw cutting machine. Dimensions of therecess should comply with the requirements of the crack movement andsealant material. (See Fig. 20.6).

2. Clean the recess of dust and debris by wire brushing followed by air-blastingwith oil-free compressed air.

3. Coat the surfaces of the recess with primer as specified by the sealantmanufacturer.

4. Place a bond breaker (such as polyethylene strip, pressure sensitive tape orother material that will not bond to the sealant) at the bottom of the recess.

5. Fill the recess with flexible sealant as per manufacturer's instructions. Wherethe concrete is carbonated or contaminated with chlorides or hasdeteriorated due to corrosion of reinforcement, it must be broken out (refersub-procedure 19.2) and replaced and a sealed movement joint formed asdetailed above.

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21.11.3 Repair procedure for surface seal

1. Narrow cracks subject to movement, where aesthetics are not important andwhere the structure is not subject to traffic, may be sealed with a flexiblesurface seal. (See Fig. 20.7.)

2. Clean the concrete surface adjacent to the crack of laitance andcontaminants such as grease and oil. (Refer sub-procedure 19.11).

3. Coat the concrete surface along the crack in approximately 100mm widestrips with a primer recommended by the sealant manufacturer.

4. Place a 20mm wide bond breaker strip over the crack.

5. Apply minimum 60mm wide and 3mm thick flexible joint sealant over thebond breaker with a trowel.

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22. Patch repairs

22.1. Engineering discussion

Patch repairing is employed to restore small areas of otherwise sound concretedamaged by spalling, scaling, honeycombing and impact. Patch repairs aregenerally trowel applied, require none or minimum formwork and their thickness islimited to a maximum of about 100mm in high build applications.

Depending on the type, location and extent of damage and urgency of repairing,patch repairs may be carried out with Portland cement mortars, latex modifiedcementitious mortars or epoxy mortars. Characteristics of different types of mortarshave been given under Chapter 16 "Repair Materials". However, preference shouldbe given to cementitious or latex modified cementitious materials for compatibilitywith concrete.

If ordinary Portland cement is used in the mortar, the patched surface would tend tobe darker than the surrounding concrete. Therefore, a part of the Portland cementshould be replaced with white cement to lighten the patch. It is desirable to make atrial patch to achieve matching colour.

Mortar of a consistency suitable for trowelling usually does not contain enoughcement paste to coat the old concrete surface or the reinforcement adequately anda bonding coat of cement grout or polymer admixtures must be used. Bondingcoats containing polymer admixtures dry quickly and work must be organised so thatapplication of mortar follows the bonding coat within a few minutes.

22.2. Repair procedure with cement-sand mortars

1. Remove all damaged, unsound and contaminated concrete and prepare theedges of the patch area as per sub-procedure

2. Clean concrete substrate as per sub-procedure 19.3 and saturate it withwater for 24 hours prior to repair as in sub-procedure 19.7.

3. Clean the reinforcement if exposed and contaminated with rust as per sub-procedure 19.5.

Note: Patch repairs are generally done to sound concrete. Repairs fordeterioration due to corrosion are treated differently.

4. Select appropriate patch material and bonding coat for the job. It may be aproprietary pre-packaged formulation or site-mixed preparation. Forproprietary products carefully follow the manufacturer's recommendations.

For common repair jobs a cement and coarse sand mixture in the ratio of 1:3by weight is generally adequate. If the patch must match the colour of thesurrounding concrete a blend of Portland cement and white cement may beused. Normally, about one-third white cement is sufficient, but the preciseproportions can only be determined by trial.

5. Prepare the cement-sand mortar by mixing with minimum amount of water.Slump of the mix for shallow patches should not exceed 25mm.

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To minimise shrinkage in place, allow the mortar to stand for half hour aftermixing and then re-mix prior to use. Do not re-temper with water.

6. Apply the bonding coat to the concrete substrate and to the reinforcement asper sub-procedure 19.7 and 19.8.

7. Apply the mortar immediately following the bonding coat. The mortar shouldbe forcibly projected or dashed onto the substrate and placed in layers about10mm thick. Compact each layer thoroughly over the entire surface using ablunt piece of wood or hammer. Each layer should be cross-scratched tofacilitate bonding with the next layer. Generally, there need be no timedelays between the layers. For vertical and overhead repairs of considerablethickness, in order to prevent sagging of the mortar, the repair may be limitedto about 50mm thickness at one time, and should then be kept moist for aday before applying the successive layer.

8. Finish the patch to the texture of the surrounding concrete by using similarform material and hammering with a mallet or by wood floating or steeltrowelling as necessary.

9. Start curing as soon as possible. Follow sub-procedure 19.10.

22.3. Repair procedure with polymer modified cementitious mortars

1. The repair procedure is the same as for cement-sand mortars, except for thedetails noted below

2. The proportion of polymer admixtures to be added should be as permanufacturer's recommendations.

3. The working time of polymer modified mortars is relatively short. Therefore,limit the quantity of mix for a particular job such that it can be placed,compacted and finished within the working time - about 20 minutes.

4. Soak the concrete substrate with water for one hour before applying bondingcoat.

5. Apply polymer based bonding coat to concrete substrate and reinforcementas per sub-procedure 19.7. Polymer in the bonding coat should be the sameas in the repair mortar.

6. Place the mortar in the patch without any delay and before the bonding coatcan dry. Compact and finish within the working time of the mortar.

7. Do not re-work or manipulate the mortar after the latex has coalescedotherwise cracking will occur on drying.

8. Adopt the curing procedure for polymer modified mortars as laid down insub-procedure 19.10.

22.4. Repair procedure with epoxy mortars

Note: Patch repairs with epoxy mortars require special skills and should be

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entrusted to personnel experienced in mixing, handling and applying epoxymaterials. The following notes are for guidance only.

1. Do not carry out repairs with epoxy-based materials at low temperatures as itis difficult to get the mixture to harden quickly enough.

2. Restrict application of epoxy mortar to thin sections, say not exceeding20mm.

3. Prepare and clean the patch area as per sub-procedure 19.1 and 19.3. Theconcrete surface should be completely dry.

Note: Patching that is thin enough to be appropriate for repair with epoxymortar is not likely to extend down to the reinforcement, but if it does,clean the reinforcement as per sub-procedure 19.5.

4. Mix the epoxy components and aggregates accurately as recommended bythe manufacturer in a high shear mixer, preferably in whole pre-weighedbatches as supplied by the manufacturer.

Working time of resin-based materials is very short. Mix the quantities thatcan be easily placed and finished within the working time. Also, a largebatch of resin-hardener mixture has a shorter working life than a small batch.

Handle the materials cleanly to avoid contamination of both the resinmixtures and the people working with them.

5. Prime the concrete substrate (and reinforcement, if exposed) with the sameliquid resin mixture as used for the epoxy mortar. (Sub-procedure 19.7).

6. Apply the mortar with a trowel immediately following the bonding coat andfinish the repair before the resin hardens.

7. No curing is required for resin mortar patches.

23. Recasting with concrete

23.1. Engineering discussion

Recasting with concrete is required to replace concrete that has been severelydamaged and non-removal of which would lead to further deterioration and couldimpair the strength, stability and functioning of the structure. The cause of suchdamage could be corrosion of reinforcement, fracturing, spalling, delamination,honeycombing, leaking joints or any other.

Recasting with concrete generally involves removal of deteriorated concrete,cleaning up the substrate and reinforcement, setting up formwork and placement ofnew concrete.

The entire repair scheme must take into consideration the special requirements forthis kind of work, that are:

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23.2. Concrete mix design

The concrete mix used for recasting must be capable of producing highlyimpermeable concrete with adequate workability and low shrinkage.

Ideally the repair mix should be made with the same type of aggregate as theoriginal concrete to minimise thermal stress. It is also usually necessary to use asmaller (10mm) maximum aggregate size for repairs because the space for placingconcrete is often restricted. Care should be taken to ensure that aggregate will notreact with alkali from the cement particularly as a rich mix will be used.

To minimise stresses caused by drying shrinkage, the water:cement ratio should notexceed 0.4. In some situations, it may be helpful to add shrinkage-compensatingadmixtures to the mix. These admixtures work by causing slight expansion to offsetshrinkage and thermal contraction.

The repair concrete should have a high cement-paste content for bonding with oldconcrete and reinforcement and to provide high alkalinity for the protection of steel.The mix should have a minimum cement content of 410kg per cubic metre ofconcrete. For the highest concrete quality it is preferable to use both 35:65 SAcement and silica fume in the mix.

The conflicting requirements of low shrinkage and high cement content can bereconciled to some extent by the use of a super plasticiser to give a mix of mediumworkability (100 to 150mm slump) at a very low total water content.

The grading of aggregate and sand must be chosen to make a dense concrete andto keep bleeding to the absolute minimum, especially for soffit repairs wherebleeding can lead to complete separation between old and new concrete.

For small repair jobs concrete may be mixed at site, using a small concrete mixer.On site batching should be avoided. It is preferable to make trial mixes and thenpre-batch into convenient sized bags off site with only specified quantities of waterand superplasticiser to be added at site. All materials must be weigh batched.

A suggested mix design for small scale repairs is given below. These quantities willmake about 0.03 cubic metre of concrete and would fully charge a small mixer.

(Source: Austroads 1991 -"Bridge Management Practice").

Cement- Preferred 35:65 SA 13.0 kg(Type SA or A acceptable)

- Silica fume 0.5 kgIf silica fume unavailable, use 13.5kg cement)

10mm Crushed Aggregate (assumed solid SG 2.7) 36.0 kg

Sand (assumed with 2% water content) 18.5 kg

Water (maximum) 5.4 litres

Superplasticiser (nominal) (dependent upon the brand) 25 ml

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The on-site mixer must be rinsed out and charged with the dry components, then 4.5litres water added, followed by two minutes mixing. Superplasticiser should beadded while mixing continuously, and then more water added until the design slumpis achieved. A maximum of 0.9 litres extra water will be needed if the mix design iscorrect, otherwise the superplasticiser quantity should be reviewed.

Where placement quantities are large enough to justify, pre-mixed concrete from acommercial plant may be used. The mix used should have a minimum cementcontent of 410kg per cubic metre and a maximum water/cement ratio of 0.40 asspecified before.

23.2.1 Formwork

Requirements of formwork for recasting have been discussed in sub-procedure19.9.

23.2.2 Compacting recast concrete

Where concrete is replaced by recasting, it must be made to flow into place toexclude all air voids because the space for placing the concrete and using internalvibrators is often very restricted. The most practical way of achieving goodcompaction is to place the concrete in small quantities and vibrate it as the workproceeds.

External vibrators on the formwork are very effective for inducing flow andcompacting concrete in awkward places.

23.2.3 Placement of concrete

The method of placement depends very much on the individual situation but itshould ensure that well compacted concrete completely fills all voids.

Where soffits are recast, holes may be drilled through the slab and concrete placedfrom above. (See Fig. 22.1.) Alternatively, soffit formwork can be extended toprovide a series of hoppers at the open sides for feeding superplasticised "flowing"concrete, or the concrete can be pumped to the farthest point of the void through apipe that is gradually withdrawn as concreting proceeds.

Whichever method is used, any void that is confined on all sides must be filled fromthe lowest or farthest points to ensure that air is driven out as the concreteadvances, and if necessary vent holes or pipes may be provided to allow escape ofthe air.

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23.3. Repair procedures

- Support the existing structure adequately to safeguard against instability anddeformation during repair work.

- Remove all deteriorated or damaged concrete and prepare edges of repairwork as per sub-procedures 19.1 and 19.2.

- Examine the reinforcement for loss of section due to corrosion. If cross-sectional area of the reinforcement has reduced by more than 15%, arrangeextra reinforcement as necessary.

- Clean the concrete substrate and reinforcement as per sub-procedures 19.3and 19.5.

- Select a suitable bonding agent for concrete and reinforcement taking intoconsideration its limited working time available for fixing the formwork andplacing the new concrete. If concrete can be placed immediately afterapplying bonding coat, use either Portland cement grout or polymer modifiedcement grout. If delay is expected due to formwork, specially formulatedepoxy bonding agents with long working life should be used.

- Apply bonding coat to concrete substrate and reinforcement as per sub-procedures 19.7 and 19.8.

- Fix formwork, if required, as per sub-procedure 19.9.

- Place concrete in the forms by a suitable method. Compact well usinginternal or external vibrators as necessary. Finish unformed surfaces bybrooming, wood floating, steel trowelling or any other method to match theadjacent existing concrete.

- Start curing of concrete as per sub-procedure 19.10.

- Forms for load bearing structural members shall remain in position until atleast 80% of the 28 day compressive strength of the new concrete isachieved. (10 days for normal Portland cement, 7 days for high earlystrength Portland cement). Forms for non-load bearing members may beremoved after 2 to 3 days.

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- After stripping the formwork, examine the concrete for any blemishes.Repair any defective work using stiff cement mortar having the sameproportion of cement and fine aggregate as used in the concrete and bring toan even surface using wooden float.

23.4. Replacing bearing pads

23.4.1 Engineering discussion

Removal of damaged or deteriorated bearing pads may be necessary in severalsituations, such as:

Cracking Shattering Crushing Pier/Abutment - cracked and shattered. To lift/lower bridge to suit track height and superelevation

Regardless of type of deterioration, all unsound and disintegrated, bearing padsmust be removed.Carry out survey to restore track to correct height and superelevation as required.

Consideration MUST be given to repair/replace defective H.D. bolts.

Consideration MUST be given to weather conditions ie buckling of track in hotweather.

If the repair is to be carried out with the bridge open to traffic, select suitablesupports for the girders.

If H.D. bolts need replacing consider drilling new hole in bed plate for new bolt orreplace bed plate - chemical anchor new H.D. bolts.

If bearing pads are to be repaired/replaced under traffic and girders to be supportedfrom ground, prepare and erect support at least 1 week beforehand to ensuresupport does not drop under load.

23.4.2 Procedure outline

1. If bed plates are to be raised with girders, ensure bolts/studs connectingbearing plate to bed plate are in place.

2. Remove nuts from H.D. bolts or unscrew nuts to allow bed plates to beraised to correct height.

3. Raise the girders by jacking the minimum amount required to enablecompletion of the replacement operation. See 7.6.5.2.

4. Remove damaged bearing pad.

5. Assess conditon of H.D. bolts and repair/replace as required.

6. Clean concrete/masonry substrate.

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7. Locate bed plate to correct height.

8. Apply bonding coat to concrete/masonry.

9. Erect formwork.

10. Place new bearing pad material in formwork.

11. Allow time to cure.

12. Lower girders and screw up H.D. bolts.

Replacing bearing pads see the following:

7.6.5 Repairing bearing plates - Procedure outline.

16.3 Types of repair material.

17.3 Selection of repair method.

18.4 Steps in repair work.

19.1 Removing damaged concrete.

19.3 Cleaning concrete substrate for patch repair and re-costing.

19.7 Applying bonding coat to concrete.

19.9 Formwork for re-coating concrete.

24. Repairs for corrosion

The presence of corrosion in concrete structures is generally known when cracksoccur. Extensive corrosion shows up in long cracks running along the reinforcementleading to spalling and delamination/ or, corrosion may be localised due to impactdamage, honeycombing or water penetration.

In all cases it is advisable to remove the concrete and examine the extent ofcorrosion immediately. Where the corrosion is extensive, concrete should be testedfor chloride penetration and carbonation also.

If it is determined that patch repairing or re-casting with new concrete will be cost-effective then the procedures in Chapters 21 and 22 should be followed rigorously.The repair should also include cleaning the reinforcement and possibly applyingprotective treatment (refer sub-procedure 19.5 and 19.8).Consideration should begiven to the application of a protective coating to the concrete surface to limit furtheringress of chlorides and carbonation (refer Chapter 25).

25. Sprayed concrete

24.1 Engineering Discussion

A description of sprayed concrete has been given in Section 16 "Repair Materials".Sprayed concrete is highly specialised work requiring skilled operators, specialmixes, equipment and techniques. For detailed information reference should bemade to "Recommended Practice Sprayed Concrete" published by Concrete

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Institute of Australia, 1987.

Spraying is most suitable when large areas of relatively thin concrete (30 to 60mm)have to be applied, for example: in restoring or increasing the cover overreinforcement, replacing delaminated concrete, linings and coatings on rock facesand tunnel walls, stabilising excavations, and encasement of steelwork.

Where sprayed concrete is more than 50mm thick and is to withstand tensile and/orshrinkage and temperature stresses, steel fabric reinforcement should be used.Recommended fabrics are any 100 x 100mm wire spacing or greater, eg. F41, F81or more. Expanded metal meshes and heavy concentration of small-grid wire meshare not recommended as they tend to produce rebound problems. Where largediameter bars are provided, exceptional care should be taken in encasing them asthey tend to cause voids or rebound inclusions.

Sprayed concrete may be screeded and trowelled to a plane fine-textured finish, butworking may impair bonding with the background. Methods of finishing are given inthe reference given above.

Sprayed concrete employs a relatively dry mix and is often used in thin sections.Proper curing to ensure full hydration of the cement is therefore essential. Thesurface should be kept continuously wet for at least seven days. If water curing isimpractical, approved curing compounds or impermeable sheets (such aspolythene) should be used. Curing compounds may be permitted where:

drying conditions are not severe no additional concrete is to be sprayed no paint is to be applied it is aesthetically acceptable

Due to surface roughness, liquid-membrane curing compounds should be applied attwice the rate required for ordinary concrete work.

It is essential that sprayed concrete work be entrusted to specialist contractors.Accordingly, only brief outlines of repair procedures are given.

25.1. Repair procedure

1. Remove all damaged and unsound concrete from the structure to berepaired as per sub-procedure 19.1. Concrete should be so removed so thatthere is no abrupt change in thickness of repair and any square shouldersshould be tapered.

2. Clean concrete substrate and exposed reinforcement as per sub-procedure19.3 and 19.5.

3. Fix required fabric reinforcement rigidly to prevent vibration during spraying.

4. Fix formwork as required to restrict the boundaries of sprayed concrete.(See Fig. 24.1.) Coat the formwork liberally with form release agentscompatible with the spray mix.

5. Protect adjacent buildings, trees, garden, etc. from dust and reboundconcrete, that would ensue during spraying operations, with suitable covers.Ensure that local work safety regulations are adhered to.

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6. Check operation of all spraying equipment before commencing work.

7. Wet the substrate with an air/water blast before spraying concrete.

8. Apply spray concrete in layers. Build up each layer by making passes of thenozzle over the working area in a pattern of overlapping loops. To minimiserebound, the nozzle should be held nearly perpendicular to the surface beingsprayed at a distance of between 0.6m and 1.2m.

9. Finish the surface by screeding or trowelling if required.

10. Commence curing as soon as possible.

26. Protective coatings

26.1. Engineering Discussion

Protective coatings on surfaces of concrete structures are not exactly repairmethods. They are protective or preventive measures applied to inhibit thedeterioration process caused by environmental factors such as penetration bymoisture, chlorides and carbon dioxide.

Coatings may be applied in any of the following circumstances:

1. On surfaces of new structures for aesthetics and increased durability.

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2. On surfaces of the existing structures where tests indicate that chlorideingress and carbonation has occurred in the concrete but as yet no corrosionis evident, in which case application of coatings would help in reducingfurther deterioration. However, if there are signs of corrosion, application ofprotective coatings will not stop the corrosion. In this case the deterioratedconcrete should be removed and replaced by patch repairing or recasting.

3. On surfaces of newly repaired concrete to give extra protection againstrecurrence of deterioration and to conceal the repair work.

For whatever reason the coatings are applied, it has to be accepted that they do notlast forever and re-coating will be required from time to time as ongoingmaintenance. However, in some circumstances they could be a more economicalternative to carrying out repairs.

A large number of proprietary protective coating systems are available. Selection ofany coating will depend on the protection required, soundness of the concrete, easeof application and the cost involved. In all cases follow the recommendations of themanufacturer for health, safety and handling precautions and applicationtechniques.

Chlorides penetrate into concrete in solution form, ie. dissolved in water. Therefore,a coating that resists penetration of water will also resist chloride ingress.Silane/siloxane based penetration type coatings as well as film forming coatings thatstick well to the concrete surface and form waterproof skins are both effectiveagainst chloride penetration. However, build up of water vapour behind the film typecoatings can cause such coatings to blister and peel off unless their adhesion toconcrete is very good.

Carbon dioxide (and other acid gases in industrial environments) penetrate into theconcrete mainly as gases. Silane/siloxane based coatings are vapour permeableand therefore ineffective against carbonation. Rendering and painting is theaccepted treatment against carbonation. In this a fine cement-based render is firstapplied to the affected areas to remove surface imperfections, followed by an acrylicbased coating that prevents ingress of carbon dioxide.

26.2. Repair procedure for chloride build up(but no corrosion evident yet).

1. Ascertain the profile of chloride penetration into concrete. Determine if thechloride was inherent in the original concrete mix or it has entered later. Ifthere is no corrosion of steel yet, estimate on the basis of chloride profile andage of concrete the time to depassivation of steel (Browne, 1980).

2. Based on this estimate and if the concrete otherwise is in sound condition,decide whether to leave the concrete as it is and re-inspect after anappropriate interval or to take action to limit further chloride ingress. Thefollowing techniques can be considered as possible for controlling chlorideattack:

Silane/siloxane coating Cathodic protection Chloride extraction and re-alkalisation

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Procedure for silane/siloxane coating is given below. The other methodsrequire special technology and should be undertaken only in consultationwith the experts in the field.

3. Repair surface cracks and spalls if any by appropriate methods (referChapters 20 and 21).

4. Clean the surfaces to be coated of all contaminants as per sub-procedure19.1. Make good any blowholes and areas of substantial pitting with anapproved finishing compound.

5. Wash down the surfaces with clean water. Allow to dry for 24 hours.

6. Mask or protect adjacent areas, paints, sealants, asphalt or coated surface.

7. Apply silane/siloxane in at least two flood coats using a low pressuresprayer. Repeat application until correct coverage is achieved asrecommended by the manufacturer. (Silane/siloxane is also used as a primerfor some protective coating systems. Allow to dry for at least two hoursbefore applying another coating).

26.3. Repair procedure for carbonation(but no corrosion evident).

1. Monitor the situation at periodic intervals by phenolphthalein tests todetermine the progressive depth of carbonation front. No protective surfacetreatment is necessary until the carbonation front reaches the steelreinforcement.

2. Once the carbonation front reaches the steel, and if the concrete otherwise isin sound condition, any of the following options can be considered to preventfurther carbonation:

Silane/siloxane primer plus anti-carbonation coating Rendering and painting Cathodic protection Re-alkalisation

Guideline procedure for rendering and painting is given below.Depending on the proprietary materials or coating system selected, exactprocedure as recommended by the product manufacturer should be adopted.

3. Repair surface cracks and spalls, if any, by appropriate repair methods (referChapters 20 and 21).

4. Clean the surface to be coated of all contaminants as per sub-procedure19.1. Make good any blowholes and areas of substantial pitting with anapproved finishing compound.

5. Wash down the surfaces with clean water. Thoroughly soak the substrate forone hour. Allow to become damp dry without residual water.

(Instead, a primer may be applied as recommended by the productmanufacturer).

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6. Apply cement-based render with a trowel from "feather edge" to 3mmthickness. Allow to set partly before finishing finally with trowel, or spongefloat, as required.

7. Cure the render with fine spray of water or a curing material recommendedby the manufacturer. The curing material must be compatible with the anti-carbonation coating proposed to be applied. Allow at least 48 hours beforetop coating.

8. Apply the selected protective coating as per manufacturer'srecommendations. The coating should be pinhole free. One or two coatsmay be required as per product used.

27. References

1. Bridge Management Practice - AUSTROADS 1991.

2. Manual for Assessment, Maintenance and Rehabilitation of Concrete Bridges- VICROADS 1990.

3. Concrete Structures, AS3600.

4. Methods of Testing Concrete, AS1012.8-1986.

5. Durable Concrete Structures - S Guirguis, CEMENT AND CONCRETEASSOCIATION OF AUSTRALIA, TN57 (1989).

6. Recommended Practice Durable Concrete - CONCRETE INSTITUTE OFAUSTRALIA (1990).

7. Cracking of Concrete, Its Importance, Prediction and Control CONCRETEINSTITUTE OF AUSTRALIA, 1985.

8. Recommended Practice Sprayed Concrete -CONCRETE INSTITUTE OFAUSTRALIA, 1987.

9. Alkali-Aggregate Reaction in Australian Concrete Structures A Shayan,CSIRO.

10. Repair of Concrete in the Marine Environment: Cathodic Protection vsChloride Extraction - F G Collins and P A Farinha, AUSTRALIAN CIVILENGINEERING TRANSACTIONS, February 1991

11. Repair and Maintenance of Concrete Bridges with Particular Reference tothe Use of Epoxies - P M Palmer (MRD, WA), NAASRA Bridge MaintenanceSeminar Proceedings, 1979.

12. Corrosion Protection - S F Pollard (ex DMR-NSW) NAASRA BridgeMaintenance Seminar Proceedings, 1979.

13. Corrosion Damaged Concrete Assessment and Repair - Peter Pullar-Strecker, BUTTERWORTHS.

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14. Deterioration, Maintenance, and Repair of Structures Johnson Sydney M,McGRAW HILL

15. Causes, Evaluation and Repair of Cracks in Concrete Structures -ACI224.1R-84.

16. Guide for Repair of Concrete Bridge Superstructures ACI 546.1R-80.

17. Guide for Making a Condition Survey of Concrete in Service ACI 201.1R-68.

18. Standard Specification for Repairing Concrete with Epoxy Mortars - ACI503.4-79.

19. Guide for the Use of Polymers in Concrete -ACI 548.1R-86.

20. Standard Specification for Repairing Concrete with Epoxy Mortars - ACI503.4-79.

21. Guide to Joint Sealants for Concrete Structures -ACI 504R-77.

22. Routine Maintenance of Concrete Bridges - ACI 345.1R-83.

23. Mechanisms of Corrosion of Steel in Concrete in Relation to Design,Inspection and Repair of Offshore and Coastal Structures - R D Browne -ACI SP-65 (1980) pp 169-204.

24. AASHTO Manual for Bridge Maintenance, 1987.

25. Guide to Investigation of Structural Failures - Jack R Janney, ASCE.

26. Bonding New Concrete to Old - Bruce Suprenant, CONCRETECONSTRUCTION, July 1988.

27. Selecting Repair Materials -James Warner, CONCRETE CONSTRUCTION,October 1984.

28. How do you Prevent Corrosion? -CONCRETE CONSTRUCTION, February1988.

29. Equipment for Cleaning or Preparing Concrete Surfaces for Repair -BSuprenant and W Malisch, CONCRETE CONSTRUCTION, November 1986.

30. Cracks in Structures -James Hill, CONCRETE CONSTRUCTION, March1988.

31. Cathodic Protection of Reinforced Concrete, The Long Term Repair Strategy- Brian Wyatt, CONSTRUCTION REPAIR, February 1987.

32. Concrete Cracking in Coastal Areas: Problems and Solutions A Nanni and WL Lista, CONCRETE INTERNATIONAL, December 1988.

33. Chemical Grouting of Water-Bearing Cracks - S T Waring, CONCRETE

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INTERNATIONAL, August 1986.

34. The Use of Polymers in Concrete Repair - J D N Shaw, CIVILENGINEERING, June 1983.

35. Product Technical Literature:

- Fosroc- Sika- Amatek- Epirez- Ciba-Geigy- ICI- W R Grace- Master Builders Technologies- Emhart Bostik- Cementaids- Vivacity Engineering- Remedial Concrete Engineering- Denso Dimet

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Bridge Repair Manual

Part 4Masonry Repairs

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28. Introduction to masonry repairs

28.1. General

Several of ARTC’s bridges are constructed with masonry abutments, piers and wingwalls with superstructures of steel girders, reinforced concrete slabs or precastprestressed beams, while some are masonry arches supporting the railway betweenspandrel walls. All such masonry structures are generally very old and consist ofbrickwork in cement or lime mortar. Very few bridges consist of stonework, thoughstone copings and bearing sills on top of brick piers and abutments are quitecommon.

Masonry structures, like any other, can deteriorate under the effects of environment,foundation movements, impact damage and so on. As a result, masonry elementsfret, crack, move or become disfigured.

This part of the Manual lists the causes of damage and summarises methods ofrepair for masonry structures. It does not cover, however, the investigations andremedial measures for foundation movements and hydrological and hydraulicengineering problems such as erosion of stream beds, effects of floods etc. that maybe responsible for damage to the masonry. Reference on these matters should bemade to specialist engineers experienced in the particular fields.

28.2. Health and safety

Before undertaking any repairs all precautions should be taken for health and safetyof the workers and general public who may be affected by the work. Attention isdrawn to the Chapter "Health and Safety" that highlights the precautions requiredwhen handling specialised and hazardous materials and equipment duringmaintenance and repair work.

28.3. Acknowledgements

Much of the material for Masonry Repairs has been obtained from the followingsources that are gratefully acknowledged:

1. AUSTROADS 1991, Bridge Management Practice.

2. THE HERITAGE COUNCIL OF NEW SOUTH WALES, Technical InformationSheet 2, Masonry Renovations.

3. BUILDING RESEARCH ESTABLISHMENT, UK, BRE Digest 359 (March1991) Repairing Brick and Block Masonry.

29. Deterioration of Masonry

29.1. Causes of deterioration

The principal causes of deterioration of masonry structures are:

29.1.1 Ground movement

All masonry structures are vulnerable to cracking from excessive settlement ordifferential settlement of the foundations. The ground movements are caused by:

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variations in soil compressibility due to changes in groundwater levels or sitedrainage

loss of support due to soil erosion swallow holes, mining subsidence or local vibration effects desiccation of shrinkable clays in dry summers due to adjacent trees rehydration of clays following removal of adjacent trees inadequately compacted fill.

If significant foundation movement is suspected, it should be referred to ageotechnical consultant for investigation and advice.

29.1.2 Thermal movement

Fluctuations in temperature may set up stresses in walls restrained at both endssufficient to cause fracture or distortion of the wall. Movements of the superstructureelements, eg. steel girders, concrete beams and slabs can crack the supportingmasonry if sliding bearings have not been provided or if the bearings have corrodedand "seized".

29.1.3 Sulphate attack

Cement-based mortars may be attacked by sulphates derived from clay bricksthemselves or from sulphate bearing soils. The attack is gradual and occurs onlywhen the masonry remains wet for long periods. Sulphate attack causes expansionof the jointing mortar that may result in spalling of the brick edges, progressivecracking and deformation of the masonry.

If the wall is rendered, sulphate attack will produce horizontal cracking of therendering. Later, the rendering becomes hollow and more badly cracked andportions may fall away.

Suspected sulphate attack can be confirmed by chemical tests.

29.1.4 Expansion on wetting

Clay bricks undergo a slight "growth" after leaving the kiln, resulting in expansion ofbrickwork. In load bearing walls vertical expansion rarely causes problems, buthorizontal expansion can give rise to movement and vertical cracking of brickwork.These cracks often occur at or near the quoins of short returns, at setbacks orchanges in height or thickness of walls.

The bulk of the expansion and movement takes place quite early in the life of thestructure but can continue for up to 20 years.

Another cause of outward movement of masonry and cracking is the swelling ofmaterials used as hardcore or filling behind the walls. Some shales and clays usedas fill may swell when wetted and cause outward movement of walls.

29.1.5 Corrosion of embedded iron or steel

Corrosion of iron and steel embedded or enclosed in masonry can cause opening ofthe masonry joints, cracking of the masonry and rust staining. Where a steel beamis in contact with a brick cladding, rusting of the steel may displace the immediatelyadjacent courses of bricks beyond the main face of the masonry. Rusting of astanchion similarly covered may produce a vertical crack. Brick pedestals built

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around steel columns often crack due to rusting of the steel. The rusting ofunprotected steel cramps, brackets or reinforcement embedded in the masonry canalso cause trouble.

29.1.6 Unsound materials

Occasionally, masonry suffers damage because of unsoundness of the mortar or ofthe units themselves. For example, the presence of imperfectly slaked lime in amortar can produce effects ranging from minor pitting of the mortar to generalexpansion with deformation and cracking of the masonry. Similarly, unslakednodules of lime in clay bricks may cause "blowing" or spalling of brickwork when firstwetted.

Weak mortars are often porous; they are damaged by frost and flowing water,become friable and are easily eroded. The weakness may be due to low cementcontent or to unsuitable sand in the mortar mix or occasionally it is caused by dirtymixing water.

29.1.7 Salts

Salts in masonry may be derived from the bricks or stones themselves, from mortar,from soil in contact with the masonry or from sea water.

Salts in clay bricks or mortar produce an efflorescence that although unsightly isusually temporary and harmless to bricks.

Salts dissolved in ground water penetrate masonry from the foundations and backfillby capillary action or leak down from the fill materials above. When water reachesthe face of the wall in contact with air, it evaporates away leaving behind thedissolved salts that crystallise just below the surface of the wall. The pressuredeveloped due to crystallisation is sufficient to spall the surface layer of the masonryunits. If this process continues unchecked for a length of time, considerable loss ofmaterial may occur. The deterioration is more pronounced in the lime mortar jointsthat being more porous than brick or stone draw more water and therefore freteasily.

Masonry abutments and piers built in coastal water streams suffer damage byingress of salts from the sea water. The continuous cycles of wetting and drying inthe tidal zone causes disintegration of masonry surface by formation of salt crystalswithin its pores and subsequent eroding away of the disintegrated material by tides.

29.1.8 Abrasion

Water borne abrasive materials may abrade soft masonry. This can be particularlysignificant if the base flow of the watercourse is permitted to run along the faces ofpiers or abutments.

29.1.9 Impact force

Impact damage can be caused to masonry bridge structures by:

collision of or glancing blows from motor vehicles against masonryabutments, wingwalls and piers

derailment of trains overheight vehicles striking against the intrados of masonry arches

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impact of heavy floating logs carried by rapidly flowing streams against thebridge structure.

Impact damage must be investigated immediately to check if the strength andstability of the bridge are affected and repairs should be organised accordingly.

29.1.10 Overloading

Overloading of masonry bridge structures may occur due to the following:

vehicles with above legal limit weight increased train loads since the construction of the bridge excessive build up of road metal or ballast on the deck build up of flood debris against the structure excessive hydraulic pressures behind abutments and retaining walls due to

lack of drainage.

Overloading can cause cracking of the structure. Excessive overloads may evencause collapse.

29.1.11 Vegetation and marine organisms

The fill retained between spandrel walls over the arches and behind abutments,retaining walls and wing walls often contains sufficient water and nutrients to supporta large mass of vegetation. While growth of grass and small bush may help tostabilise backfill slopes and prevent erosion, large trees may damage the masonryby exerting pressure through their trunks and roots.

Roots and stems growing in crevices and joints exert a wedging force that can priseopen and dislodge the masonry. Lichen and ivy can chemically attack the surfacewhile attaching themselves to masonry.

Rock boring molluscs can attack masonry by means of chemical secretions.

30. Types of defects

30.1. Cracks

The commonest form of defect is cracking that occurs due to several reasons, suchas differential settlement of foundations or relative movement in members of thestructure, thermal movements, growth of brickwork, corrosion of embedded iron orsteel, impact damage and growth of vegetation in or around brickwork.

Cracking is specially significant if it is recent in origin and should be immediatelyinvestigated. Particularly, it must be ascertained if the cracks are live, ie. continuingto move and if they pose any threat to the strength and stability of the structure.

If the cracks are known to have existed for a long time and have not causedinstability or distortion, they need not be a cause of concern, though steps should betaken to repair them.

Cracks that have formed due to overload will tend to be very fine after the overloadis removed and may not need any treatment.

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30.1.1 Cracks in masonry arches

Masonry arch bridges are particularly sensitive to movements. Factors affecting thestability of arches include:

Differential settlement across an abutment or pier -causing longitudinalcracks along an arch ring.

Settlement of a pier or abutment foundation -this may cause lateral crackingacross an arch ring and settlement in the roadway or railway. It suggeststhat the arch has broken up into separate segments.

Settlement at the sides of an abutment or pier - this may cause diagonalcracks starting from the side of the arch at the springing and continuingtowards the centre of the arch at the crown.

Flexibility of the arch ring - causing cracks in the spandrel walls near thequarter points.

Outward movement of the spandrel walls due to the lateral pressure of thefill, particularly if the traffic loads are applied close to the parapet -this maycause longitudinal cracking near the edge of the arch.

Movement of the wing walls -this may cause cracking in adjoining abutmentsand arches.

30.2. Fretting

Fretting is surface damage caused by leaching of dissolved salts through themasonry, and cycles of wetting or drying. It disintegrates the lime mortar in thejoints and can cause spalling of the masonry units.

30.3. Spalling

Spalling of masonry is generally caused by accidental impact. It may beaccompanied by dislodgement of masonry units as well as cracking and dependingupon the extent of damage may cause loss of strength and stability in the structure.

Spalling due to other causes such as fretting, sulphate attack and unsound materialscan generally be recognised by inspection and repaired accordingly.

31. Assessment of deterioration

IMPORTANT NOTE:The most important thing in any assessment of damage or deterioration is to establish thatthe strength and stability of the structure are not affected. Where safety of a structure is inquestion, professional advice should be sought immediately for protecting the structure aswell as its users against further damage, collapse or injury.

31.1. General

Before any repairs are initiated, it is essential to identify the cause and extent of thedamage and whether or not the cause is still active.

31.2. Assessment procedure

1. Before proceeding, assess if detailed examination of the damage wouldrequire track closure, power outage, pedestrian and traffic restrictions,assistance from police and utility authorities, flagmen, special equipment for

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access and health and safety measures.

2. If the damage is old and has been repaired before, study previousinvestigation and repair reports if available. Examine the condition of thepast repairs and determine if they have been successful or the deteriorationis growing worse.

3. Carry out a visual inspection of the structure. If necessary, use handmagnifiers, binoculars and telephoto photography to assess and record thetype and extent of damage or deterioration.

4. Assess the possible causes for deterioration or damage (Refer Section 28.1"Causes of Deterioration").

5. Map the location, direction and extent of cracks. Examine if the cracks zig-zag through the joints or run through the masonry units. Measure the widthof cracks.

6. Ascertain if the cracks are moving by fixing strain gauges across them atsuitable locations. Cracks that are due to applied load will move immediatelywhen the load is changed (eg. under traffic passing over the bridge). Cracksmay also move under temperature variations. Measurements should bemade with and without traffic loads and for 4 or 5 times in a day to establishwhether a crack is live or not.

7. Check if any distortions have occurred in the load bearing elements such aswalls, abutments and piers as well as retaining structures.

Check verticality with a plumb line and measure out-of-plumbdistortion.

Check bulging in both horizontal and vertical directions using a 3metre long hardwood straight edge.

Assess the effect of these distortions on the strength and stability of thestructure using appropriate structural analysis methods.

8. Examine the bearing areas under steel, concrete and timber beams andconcrete slabs supported on top of the masonry walls, abutments and piers.Examine the extent of corrosion of steel bearings or deterioration of other slipjoints provided. Look for cracks in the masonry immediately under thebearings. Also ensure that there has not been a significant loss of support tothe superstructure.

9. If there are signs of efflorescence, leaching and percolation of water throughmasonry, assess the deterioration of masonry units and jointing mortar byfretting. Investigate if the earthfill behind the abutments and retaining wallsand fills between spandrel walls of the arches are properly drained. Check ifthe weep holes (if provided) are functioning. Dry weep holes indicate theymay be blocked.

10. Examine the substructures that are located in waterways for damage byabrasion, salts or marine organisms above the low tide mark. Check if thereis a significant loss of section (more than 15%) and jointing mortar.

11. Check the structure for deterioration by growth of vegetation in joints, near

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foundations and behind retaining walls and abutments.

32. Repair materials

32.1. General

Masonry is constructed from units of brick, stone or concrete joined together withcement or lime mortar.

In masonry repairs the most important material is mortar. It is essential tounderstand its function in masonry work and the basic principles that determine theselection of a "strong" or "weak" mortar in repair work.

The other materials used in repairing masonry are:

polymers (synthetic latexes) for modifying mortars synthetic resins concrete and grouts sealants The above materials are described in Chapter 16 "Repair

Materials".

Sometimes bricks, stone and concrete blocks are also needed to replace damagedmasonry. The basic criteria for their selection is to match them in colour, textureand strength with the existing work. No other discussion is needed here.

32.2. Function of mortar

Purpose of mortar in masonry work is twofold:

to seal the joints between masonry units to provide a bed for the units so that the loads are evenly distributed across

the joints.

The strength and rigidity of the masonry is mainly dependent on the strength ofbrick, stone or concrete units rather than the mortar. In fact, a very strong mortarcan do more harm than good.

32.3. Problems with strong mortars

Two difficulties arise with strong, rich mortars in masonry:

Cracking

Cracking is not usually attributable to directly applied loads, but is generally causedby differential or thermal movements between the various parts of the structure as aresult of thermal or shrinkage movement or foundation settlement.

When a strong mortar is used, fine cracks develop between the mortar and themasonry unit (brick, stone or concrete) that, as well as looking unsightly, may passright through the masonry units and permit the passage of water.

A weak mortar, on the other hand, permits the masonry work some freedom toabsorb movements without obvious cracking; and where cracking occurs it will tendto be distributed through the joints where it is comparatively easy to repair, ratherthan through the masonry units themselves.

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Thus there is improved resistance of masonry to cracking when weak mortars areused.

Fretting

Fretting happens when there has been continued evaporation from the wallsurfaces. With weak, porous mortars evaporation occurs mainly along the joints.But if a strong, impermeable mortar is used, the evaporation occurs from themasonry blocks and leads to spalling of bricks and fretting of sandstone. It is easierto repair the fretting of weak and porous mortar by repointing than to replace frettedbricks or stone blocks.

It is therefore better to use weak and porous mortar that can be repointed if need bethan to use strong mortars and having to re-build the wall.

32.4. Importance of lime in mortars

The addition of hydrated lime to the cement improves the mortar in a number ofways. It makes the mortar "soft", so it is then more able to absorb movements in themasonry and therefore minimises cracking. Lime in the mortar improves itsworkability - the mortar "comes off the trowel" more easily. It also improves its bondand its capacity for self-healing of cracks.

32.5. Basic principles

In general, the mortar should be slightly weaker and more permeable than themasonry units. For sandstock brick or sandstone, a cement:lime:sand mix (byvolume) of 1:2:9 to 0:1:2 is suitable. For normal bricks, 2:1:12 to 1:1:6 can be used.

In all cases, just enough water should be added to attain workable consistency ofthe mortar.

Do not use a clay-sand soil unless following a proven local tradition. Do not usecrushed stone unless it has been successfully used as building stone. Avoid anysand, clay or crushed stone that may contain salts.

33. Methods of repair

33.1. General

Methods are outlined for repairing the following most commonly occurring defects inmasonry structures:

Cracking Fretting Impact damage Corrosion of embedded iron or steel

Other repairs are briefly described under Miscellaneous Repairs.

Foundation and waterway repairs are beyond the scope of this manual and shouldbe referred to geotechnical and hydraulic engineering consultants respectively.

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33.2. Steps in repair work

Refer to Section 18.4: "Steps in Repair Work", under Concrete Repairs. Basically,the same process should be carried out for repairing masonry structures.

33.3. Strength and stability

It is not always easy to judge from appearance how far the strength and stability ofthe structure will be affected by damage or deterioration. But in general, simplecracks, even wide cracks, may not be too serious provided the masonry is notdistorted or much out of plumb.

If it is established that strength and stability are not affected, repairs can safely bedelayed until movement has ceased and the weather is favourable.

If in doubt, engineering advice should be sought for assessing the strength andstability. Engineering advice should also be sought before undertaking any majorrepairs and for supporting and strengthening severely damaged structures.

33.3.1 Strength of arch bridges

For assessing strength of masonry arch bridges, reference should be made to thefollowing publications:

Department of Transport (UK):

Departmental Advice Note BA 16/84 “The Assessment of Highway Bridges and Structures”

Departmental Standard BD 21/84 “The Assessment of Highway Bridges andStructures”

33.4. Repairs of cracks

33.4.1 Engineering discussion

When the damage results in cracks that are liable to further movement, it is notadvisable to make a permanent repair until the movement has stopped. The cracksmay be left, but if there is a risk of rain or debris penetrating into the crack, the crackmay be sealed temporarily by caulking with a mastic or flexible sealant.

Distinction should also be made between two types of cracks: cracks that run moreor less diagonally, following vertical and horizontal mortar joints and cracks thatpass straight down through a line of vertical joints and intervening masonry unitsand mortar beds.

In the first case, cracks through joints can be repaired, if necessary, by repointing.

But in the second case, it has to be considered if it is necessary to cut out andreplace the cracked units.

In both cases, the decision whether or not to repair cracks will depend mainly on twoconsiderations:

if the cracks are unsightly

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if not repaired, they are likely to encourage rain penetration.

Fine cracks (up to about 1.5mm wide) are not very conspicuous and can often beignored. However, if repairs are considered necessary to prevent rain penetration,they can be sealed by low viscosity self-hardening epoxy compounds.

Wider cracks will generally require raking out and repointing the joints and cuttingout the cracked units and replacing them.

33.4.2 Repair procedure for moving cracks

(Also refer to engineering discussion in Section 20.11 "Flexible Sealants for LiveCracks"). Cracks that are subject to movements permanently (say, due totemperature movements and live loads) should be treated as expansion joints. Ifthey are not unsightly or there is no danger of water penetration through them, theymay be left as they are, otherwise they should be sealed with a flexible sealant ofwidth and depth to suit the expected range of movement.

If the expected movements are insignificant or if the crack is not to be sealedpermanently:

(This is the most common type of repair for movement cracks in masonry).

Clean the crack of loose dust and debris, oil, algae and other contaminantsby using high pressure water jets, compressed air (oil free) or vacuumsuction. Allow the surfaces of the crack to dry.

Prime the crack surfaces with a primer recommended by sealantmanufacturer.

If the width of crack is more than 5mm insert a tight fitting closed-cellpolyethylene foam backer rod into the crack. The backer rod must be pushedto a depth such that the sealant applied will have width to depth ratio of 2:1,or minimum 5mm depth of sealant. (For cracks less than 5 mm do not insertbacker rod).

Seal the crack by caulking with a flexible sealant flush with the masonry face.

If the expected movements are significant or if the crack is to be sealedpermanently:

Provide a recessed seal or surface seal as described below:

Recessed Seal

Cut a recess along the crack using a power chisel or crack cutter.Dimensions of the recess should comply with the requirements ofthe crack movement and sealant material. (See Fig. 20.6.)

Clean the recess of dust and debris by wire brushing followed byair-blasting with oil free compressed air.

Prime the surfaces of the recess with a primer specified by thesealant manufacturer.

Place a bond breaker strip at the bottom of recess. Fill the recess with flexible sealant as per manufacturer's

instructions.

(ii) Surface Seal

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Narrow cracks subject to significant movement where aesthetics are notimportant may be sealed with a flexible surface seal. (See Fig. 20.7.)

Clean the masonry surface adjacent to the crack of dirt, algae, andother contaminants. (Refer sub-procedure 19.11, ConcreteRepairs.)

Prime the masonry surface along the crack in approximately 100mmwidth with a primer specified by the sealant manufacturer.

Place a 20mm wide bond breaker strip over the crack. Apply minimum 60mm wide and 3mm thick flexible joint sealant over

the bond breaker with a trowel.

33.4.3 Repair procedure for dead cracks

Fine cracks are best repaired by epoxy injection. This method has been fullydescribed in Section 20.4, "Epoxy Injection", under "Concrete Repairs".

Wider cracks can be repaired as follows:

1. If cracks run through masonry units and mortar beds, cut out the units andremove joint mortar. Wet the masonry. Allow to dry until it is just damp (noresidual water). Install new units, bonding with mortar similar to that in theexisting wall. Avoid strong mortar and use a well graded sand to minimiseshrinkage. Where the wall is severely exposed, polymer additives may beused in the mortar to increase bond and durability provided the sand usedhas a negligible clay content.

Note: The above procedure for replacing cracked masonry units is alsoused for repairing spalled masonry.

2. If cracks run through joints only (ie. masonry units are not affected), rake thejoints (on both sides of the walls if accessible) to a minimum depth of 15mmusing a square edged tool. Clean the joints of dust and debris with a wirebrush or by oil-free air-blasting. Wet the masonry. Allow to dry until it is justdamp. Fill and point with mortar not richer than a 1:2:9 mix ofcement:lime:sand.

33.5. Fretting

33.5.1 Engineering discussion

To stop the fretting process permanently, it will be necessary to halt the flow of saltladen water through the wall. As this is not practical, the alternative is to repair orreplace the masonry units or jointing mortar that have been damaged.

Application of waterproofing membranes to the exposed surfaces of masonry with aview to stop water entering from the back face should not be considered. Themembrane type of coatings generally blister and peel off under build up of vapour-pressure from behind. The penetration type of coatings (silane/siloxane) repel theingress of water from the front such as rain but, being breathable, do not stop waterentering from the back face and evaporating from the front face. Thus the wettingand drying process is unchecked and fretting will continue unabated.

If the masonry consists of "soft" lime mortar in the joints, do not replace it with "hard"cement mortar, it will do more harm than good. As cement mortar is less perviousthan lime mortar, more of the salt laden water permeating through the wall will now

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flow through the bricks or stone. Thus while fretting of the mortar will have beenreduced, the rate of fretting of the units will increase.

33.5.2 Repair procedure for damage to jointing mortar

Note: Repointing of joints is best done in the winter as lime mortar relies onabsorbing carbon dioxide from the air to set. This process takes time and ifthe temperature is too warm, the mortar will dry out before setting. If workingin hot weather, the mortar should be lightly sprayed with water at two to fourhour intervals for a day.

1. Where the jointing mortar has been damaged without disturbing the masonryunits, rake out all loose and fretting mortar from joints, with a square edgedtool. Rake out another 20mm of mortar to make sure that all crystallised saltis removed. Rake the joints in topmost 3-4 courses to be repaired first.

2. Thoroughly wet the masonry and allow to dry till it is just damp and withoutany residual water.

3. The mortar mix for repointing shall consist of hydrated lime and washedconcrete sand (without any clay content) in the ratio of 1 lime:4-5 sand.Sand must be free of salts. Only water that is suitable for drinking should beused for the mortar.

4. Mix dry sand and lime, then slowly add water while still mixing to make a stiffmix. As the lime takes a long time to go off, prepare the mortar some hoursin advance of the repointing operation and keep it covered with damp bagsuntil used.

5. Pack joints with the stiff mortar. Ensure that no voids are left, using apointing tool to ram the mortar into the joint. (Start at the topmost joint andwork progressively down). Tool off the joint surface to match the original.

Note: Where extensive repointing is involved carry out raking andrepointing in small sections to avoid instability. For example, workon 3-4 horizontal joints at a time and limit the length of repair tomaximum 3 metres or ¼ of length of the wall whichever is less.Allow at least 24 hours for the mortar to set before raking joints inthe next section. Start at the top and work progressivelydownwards.

33.5.3 Repair procedure for damage to masonry units

Note: Spalling usually affects only a small proportion of the units in the wall.Replacing the spalled units with new units that would match with the rest ofthe wall is difficult and it may be considered to leave things as they are untilcomplete resurfacing becomes necessary. However, if matching is notessential, spalling should be repaired as below.

CAUTION:Before commencing repairs check if the stability of the wall would be adversely affectedby removal of the spalled masonry. Remove and replace only as few spalled units at atime as necessary to ensure stability at all times.

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1. Cut out the spalled units to a depth at least 20mm beyond the depth ofspalling, or remove the whole units. Remove the jointing mortar also.

2. Wash down the broken surfaces to remove dust and debris. Allow thesurfaces to dry till it is just damp.

3. Set new units (whole or sawn as required) in place of the old with a lime andsand mortar as described in 32.5.2 above.

33.6. Impact damage

Masonry spalled by accidental impact would require removal and replacement of thespalled units and repair of cracks. Repair procedure for this is the same as for widecracks. (Refer 32.4.3-1.)

33.7. Corrosion of embedded iron or steel

1. Open up the masonry to gain access to the steelwork.

2. If corrosion is not too far advanced, thoroughly clean the metal by grit-and/orwater-blasting to remove any rust. Apply a corrosion protection system tosteel.

3. If corrosion is well advanced replace the steelwork either with carefullyprotected steel, stainless steel, or reinforced concrete.

4. Rebuild masonry. Apply protective coating such as silane/siloxane toprevent moisture penetration.

33.8. Miscellaneous repairs

33.8.1 Minor displacement of masonry

Minor displacement of parts of the masonry is not very important. However, largemovements may endanger structural stability. It is advisable to find out the cause ofall movements and take steps to prevent its continuing or recurring.

When part of the masonry is displaced horizontally, rake out the joints on thatmovement has taken place and repoint.

33.8.2 Sulphate attack

Sulphate attack that is abetted by dampness is liable to continue unless themasonry can be dried out and kept reasonably dry. The repair therefore should beaimed at investigating the cause of dampness and eliminating it if possible.

If the damage due to sulphate attack has gone too far, rebuilding may be necessary,in which case use clay bricks of low sulphate content with 1:1:6 or stronger mortar ofsulphate-resisting Portland cement.

Rendering that has been damaged by sulphate attack should not be patch repaired.It is best to strip it off and allow the masonry to dry and, preferably, to remain bare.If it is necessary to render again use a weaker mix of sulphate-resisting cement.

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33.8.3 Salt water and marine organisms

Repair of masonry damaged by salt water and marine organisms is difficult andspecialised work and should be entrusted to organisations experienced in this field.

Basically, the repair consists of cleaning of the affected masonry by grit and waterblasting and protecting the masonry by epoxies or by concrete encasement.

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Bridge Repair Manual

Appendix ARepair materials

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Inclusion of specific product brand names does not imply exclusive endorsement. Theproduct mentioned is appropriate but equivalent products are likely to be available fromother supplies.

A1. Steel

Unless noted otherwise all steel sections and plates used for strengthening in repairshall be grade 250 (or higher grade if grade 250 unavailable) - to AS3678 andAS3679.

Unless noted otherwise all steel sections and plates used in replacement membersor elements shall be grade 250 (or higher grade if grade 250 unavailable) toAS3678 and AS3679.

Other steels specified for particular repairs

Grade 350 to AS3678 and AS3679

Bisalloy 80

A2. Fasteners

High strength bolts, nuts and washers shall conform to AS1252 and shall be galvanised inaccordance with AS1214.

A3. Epoxies for filling voids

Epirez 8242

Epirez 633 (moisture tolerant)

A4. Epoxies for sealing interfaces

Epirez 8242

Epirez 633 (moisture tolerant)

Epirez D5-707 NS (flexible)

Dulux Luxepoxy Barrier Coat

A5. Patch painting systems

Taubmans Interseal 2020

Dulux Amerlock 400 GF and 400

Dulux Luxaprime zinc phosphate

A6. Concrete surface coating systems

Taubmans Intergard 215 - Interthane 80 HS

Dulux Amerlock 400 GF and 400

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A7. Bearing pad materials

Megaflow epoxy flow grout

Megapoxy H dry pack grout

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Bridge Repair Manual

Appendix BGuidelines for

Management of LeadPaint on Steel Structures

Scientific Services 31.1.95

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Preface

The objective of this document is to provide guidelines for the successful management ofhazardous lead containing paints on Authority steel structures particularly when paintremoval in preparation for repainting is carried out. As these structures vary greatly inconfiguration, size, location and function, different levels of health risk to workers and thepublic and pollution risk to the environment are presented. Thus, different levels andtypes of debris management are required to ensure health risks are reduced to anacceptable level and environmental pollution regulations are observed.

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Table of ContentsPage no.

Foreword 198

Summary 198

Scope 201

General 201

Procedure 201

Step 1 Determination of the presence of lead paint 201

Step 2 Selection of painting strategy 202

Step 3 Assessment of risks to public, other workers and environment 204

Step 4 Determination of emission control level 204

Step 5 Selection of paint removal method and containment system 205

Step 6 Selection of monitoring procedures 206

Step 7 Establishment of worker protection measures 207

Step 8 Establishment of waste handling procedures 207

Step 9 Establishment of work site cleaning requirements 207

Step 10 Estimation of project cost 208

Step 11 Preparation of project specification 208

Appendices

B1 Containment 209

B2 Air quality monitoring 218

B3 Ground (soil) monitoring 222

B4 Water and sediment monitoring 226

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Foreword

Much of the Authority's structural steelwork is primed with red lead primer, for it wasstandard practice to use red lead primer on new construction until 1968 when it wasreplaced by inorganic zinc silicate primer and old construction until 1983 when it wasreplaced by zinc rich epoxy primer. While red lead primer based systems remain intact,they present no significant health or environmental pollution hazard. However, in mostinstances these systems require repair or replacement during the design life of thestructure, and we are confronted with potential health and environmental pollution hazardsassociated with lead based paint removal during the course of surface preparation forrepainting.

Lead in any form is toxic to humans when ingested and inhaled. In the majority of casesthe most cost effective method of surface preparation for maintenance painting involvesthe partial or complete removal of existing coatings by mechanical means that pulverisethe paint into small particles that may be readily inhaled or ingested. Repeated inhalationor ingestion of lead based paint particles may produce lead poisoning (plumbism) andlesser intake may adversely effect a child's mental and emotional development. Thus,these methods of paint removal give rise to two potential health problems, i.e. inhalationand ingestion of lead-containing paint by workers and the public in the vicinity of thestructure, and the deposition of lead paint particles on nearby footpaths, streets or soilareas where they may be resuspended or tracked into houses or buildings and inhaled oringested. In most instances workers may be simply and easily protected by protectiveequipment and the public by prevention of access to the work site; however, lead paintdeposition may be much more complex and difficult to manage depending on the size,shape and location of the structure.

Many structures such as bridges are located in congested, urban areas where paintremoval operations may contaminate nearby residences; business properties orplaygrounds. Other structures are located in rural settings where grazing or recreationalareas in the vicinity of the structure may be contaminated. Further, most governmentregulatory bodies perceive lead based paint pollution of soil and waterways to be aconcern and direct its control despite the inability of the scientific community to assess thedegree of hazard posed to the environment.

Thus, the need exists for sound management of lead based paint coatings on steelstructures. This document addresses the issues critical to such management for thepurpose of facilitating selection and implementation of practicable, cost effectivemaintenance programs that minimize health hazards to workers and the public andpollution hazards to the environment.

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Summary

Lead in any form is toxic to humans when ingested or inhaled. Red lead paint removal bymechanical means, particularly by abrasive blast cleaning that is the most effectivemethod of surface preparation to achieve protection from corrosion, introduces leadbearing particulate matter into the atmosphere. This gives rise to two potential healthproblems i.e. inhalation of red lead primer particles by the operator, adjacent workers ormembers of the public in the immediate vicinity of the structure and deposition of red leadprimer particles on soil, footpaths or other areas where it may be resuspended or trackedinto houses or buildings and ultimately inhaled or ingested by the occupants.

Operators and adjacent workers may be simply and adequately protected from inhalationof red lead primer particles by air-supplied respirators and the general public by securitymeasures that prevent access to the immediate vicinity of the work.

The red lead particle deposition problem may be much more difficult to deal withdepending on the size, shape and location of the structure. Although most lead paintparticles fall within a few metres of the removal operation when dry abrasive blastcleaning, many are small enough to be carried aloft and deposited at much greaterdistances from the work area. Thus, urban bridges adjacent to businesses, residences orplaygrounds exposed to the lead laden blasting plume require greater control of blastingdebris than bridges in isolated rural settings.

The comprehensive U.S. Transport Research Board Report 265 "Removal of Lead BridgePaints" that specifically addresses health and environmental issues associated with thisoperation concludes "there is little evidence that lead compounds used in bridge paintsare hazardous to the environment when they are removed". This is attributed to the redlead primer's stability and insolubility in water characteristics that are such that it does noteasily break down and introduce free lead into either soil or water. Nevertheless,government regulatory bodies perceive lead based paint pollution of soil and waterways tobe a concern and direct its control.

Bridges over soil areas still present the hazards of resuspension and tracking, and bridgesover waterways present the hazard of swimmers ingesting that small portion of paintdebris that does not immediately settle to the bottom creating a scum on the surface of thewater that can last for some time and be carried some distance. Therefore, reasonablecontrol of blasting debris is in order in both situations.

Most bridges in rural areas and some in metropolitan areas that are not within 50 metresof a residence or other occupied dwelling may be dry abrasive blast cleaned and safelydealt with by means of ground tarpaulins to collect spent paint debris and abrasive. Thetarps should extend 2 metres beyond the edges of the bridge. Further, care should betaken in rural areas to ensure livestock do not have access to grazing area in theimmediate vicinity of the structure during the course of the contract. Bridges overwaterways should have tarpaulins arranged to catch spent blasting debris/direct it to thebank for collection and disposal. Further, any scum that forms on the water from blastingdebris should be contained with a floating boom device to prevent it from movingupstream or downstream and collected daily.

Bridges in built up metropolitan locations require significantly more stringent measures tocontain and collect debris generated during dry abrasive blast cleaning. In addition toground tarpaulins, drapes or a completely sealed enclosure may be required dependingupon the proximity of businesses, residences, schools, playgrounds or other sensitivereceptors. Where a dust free operation is dictated, wet abrasive blast cleaning may be in

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order. The higher risk of debris resuspension and tracking presented by metropolitanareas necessitates meticulous "housekeeping" procedures.

Wet abrasive blast cleaning and total debris containment introduce dramatic project costincreases to the extent the cost of a normal painting project may be multiplied three to fivefold. In view of the number of red lead primed rail bridges throughout the state, the cost ofspecifying these controls across the board is unsustainable and will rapidly bring criticalbridge repainting to a halt. As all bridges do not present the same degree of hazard tohuman health or the environment, it is reasonable to vary the control system. Thus,Maintenance Engineers should treat each structure on its own merit carefully assessingthe hazards presented and specifying appropriate controls to adequately protect humanhealth and comply with governing environmental legislation. This approach should enablea viable bridge painting program to be carried out.

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Scope

This document provides guidelines for the management of lead-containing paint onindustrial structures. It provides information for determining whether lead is present on astructure, selecting an appropriate maintenance strategy and implementing appropriatelead paint emission controls during paint removal in preparation for painting to ensurepotential health risks to workers and public are reduced to an acceptable level andenvironmental pollution regulations are observed. This guide does not addressrequirements for evaluation of worker health and safety that should be carried out inaccordance with regulatory requirements.

General

The successful management of an industrial structure coated with lead-containing paintrequires consideration of the function, design life and service environment of the structure,condition of the existing coating system, coating systems that will be effective in theservice environment, hazards associated with lead paint removal to workers, the publicand the environment and program cost. These factors and their many intertwinedelements need to be judiciously dealt with in a logical and systematic manner forsatisfactory painting program selection and implementation to take place. Thus, theseguidelines are presented in the form of a step by step procedure to facilitate theseconsiderations when designing a lead-containing paint management project.

Procedure

The procedure comprises the following steps:

Step 1 Determination of the presence of lead paint.

Step 2 Selection of painting strategy.

Step 3 Assessment of project risks to the public, other workers and the environment.Step 5 Selection of paint removal method and containment system.

Step 6 Selection of monitoring procedures.

Step 7 Establishment of worker protection measures.

Step 8 Establishment of waste handling procedures.

These steps as described below may require modification to accommodate peculiarstructures, locations or regulations. Further, there may be circumstances where small,isolated patch repairs or repairs to small structures far from the public or a waterway areto be carried out, and it may be unnecessary to follow the procedure except for regulatoryrequirements concerning worker protection and waste handling.

Step 1 Determination of the presence of lead paint

The presence of lead paint may be established by reviewing the historical painting recordsof the structure if these records are complete and include its entire painting history fromoriginal painting through last maintenance painting. If historical records are incomplete,the presence of lead paint may be determined by chemical field testing or laboratory testsof representative paint samples in accordance with AS/NZS 1580.501.1 or atomicabsorption spectroscopy.

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A paint film is considered to be lead-containing if it has 1.0% or more lead or leadcompounds by weight in the dry film. Structures showing paint work with this level of leadshould be dealt with in accordance with these guidelines.

Step 2 Selection of painting strategy

The following maintenance painting strategies are available:

(a) No painting. When a lead-containing paint is in good condition, tightly adhering tothe substrate, there is no hazard; thus, the option of leaving the coating alonemay be appropriate.

- If the coating has poor film integrity or shows poor adhesion to the substrate,consideration should be given to potential structural problems due to furthercorrosion and the possibility of the surrounding area being contaminated byflaking and peeling paint. Again, the option of leaving the coating alone subject tocarrying out periodic inspections to monitor coating deterioration may beappropriate.

-(b) Overcoating. When a lead-containing paint or system is adhering tightly to the

substrate and showing satisfactory film integrity, it may be contained on thestructure for an extended period of time by overcoating it with another topcoat orpaint system if its film thickness is not so great that the additional weight of theovercoat will weaken or break the bond between the existing system and thesubstrate.

Prior to overcoating, the existing paint system should be cleaned to remove dust,dirt, grease, oil, loose paint and other contaminants to maximize adhesion. Theovercoating material isolates the existing system from the environment therebyeliminating any hazard.

A number of systems are recommended for this application by the Paint Industry,and a few are detailed below:

(i) two-pack epoxy sealer with various topcoats;

(ii) two-pack, high build epoxy mastic;

(iii) single pack, moisture cured, polyurethane topcoat pigmented with zincor aluminium;

(iv) water borne acrylic primer with acrylic topcoat;

(v) oil modified alkyd topcoat with corrosion inhibiting pigment.

When considering this option, one should be particularly cautious where theexisting system's film integrity or adhesion to the substrate is suspect and guidedby the recommendation of the manufacturer of the overpainting system..

(c) Spot or localized repair Where a structure is exhibiting localized coatingbreakdown and steel corrosion products, surface preparation of these areas,priming and application of a finish coat to the localized areas or to the whole ofthe structure may be cost effective options depending upon the extent of thesurface area to be repaired. In this instance, a major risk with overcoating is

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inaccurate assessment of the condition and adhesion characteristic of theexisting lead based paint system, i.e. if either is poor, very early coating failurewill occur. When spot (patch) painting, care should be taken to ensure the repairsystem paint products are compatible with the existing system and provide longterm performance in the service environment.

(d) Total coating removal and replacement Surface preparation of the entirestructure, to the extent that all existing coatings are removed and a newprotective system is applied, may be a cost effective option depending upon thedesign life of the structure, despite the high short term costs associated withcoating removal, containment and disposal.

(e) Demolition and replacement of the structure It may be cost-effective to replacethe structure rather than removing and replacing the coating. Costs associatedwith the construction of field containment, the controls over emissions, andworker and environmental protection are applied to a new structure. The risk ofenvironmental, worker, or public contamination is very low, the service life of thestructure is optimized and the lead paint coated steel can be smelted andrecycled. A disadvantage of this option is the potential disruption to plantprocesses or the travelling public while the structure is demolished and replaced.

The following considerations should be taken into account when selecting a cost-effective painting strategy:

(a) Coating condition

(b) Service life of the structure

(c) Service environment of the structure

(d) Surface coating systems that will be effective in the service environment

(e) Method of surface preparation required for the coating system to performeffectively and its emission potential.

(f) The need to keep the structure or facility operational

(g) Proximity of the work to other facility workers or the public

(h) Proximity of the work to environmentally sensitive areas.

The major consideration in selecting a painting strategy is existing coating systemcondition. Accurate assessment of this condition is critical to selection of a costeffective painting strategy and should only be carried out by staff with expertise inthis field.

As the following steps are completed, it may be necessary to reassess thesuitability of the selected strategy and modify it as required.

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Step 3 Assessment of risks to public, other works and environment

The potential impact of lead-containing paint emissions on the health of the nearby public,adjacent workers other than workers performing paint removal, fixing containment andcollecting debris and the surrounding environment determines the degree of projectemission control.

The public and adjacent worker risks are estimated by assessing their proximity to thework and how often they frequent the proximity zone.

The risk to the public is estimated as nil, low, moderate or high by using the followingtable:

Public Health Risk Assessment

Frequency of public presencePublicproximity to

site Never Rare Occasional ContinualClose< 20 metres -- Moderate High High

Moderate20-50 metres -- Low Moderate High

Far> 50 metres -- Low Low Low

No Access Nil -- -- --

The risk to the adjacent workers is estimated as nil, low or high by using the followingtable:

Health risk to adjacent workers and other workers on site

Frequency of presence of personnelProximity tosite

Rare Occasional ContinualClose< 20 metres Low Low High

Moderate20-50 metres Nil Low Low

Far> 50 metres Nil Nil Nil

The environment risk is estimated by assessing the proximity of sensitive environmentreceptors such as oyster beds, drinking water intakes or market gardens to the work. It isestimated as low if sensitive receptors are not within 50 metres of the work and high ifsensitive receptors are within 50 metres of the work.

The distances nominated for proximity indicators may be varied to accommodate unusualstructure heights or locations, and in some instances a scale plot plan of the project siteand surrounding area may be of benefit.

Step 4 Determination of emission control level

The three previously determined risk indicators are combined in the matrix shown below

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to establish the level of emission control for the project. After entering the matrix with theenvironmental risk indicator (low or high), the adjacent work and public health riskindicators are entered on that half of the matrix and the intersection of these two indicatorsshows the level of emission control required for the project.

Risk to adjacent workers

Nil Low High Nil Low High

High A A A A A A

Mod B B A A A A

Low C C A B B A

PublicHealthRisk

Nil C C A B B A

Low High

Environmental Impact

A -a high level of control where minimal emissions are allowed

B -a moderate level of control where limited emissions are allowed

C -a low level of control where limited emissions are allowed.

Step 5 Selection of paint removal method and containment system

The following factors should be considered when selecting the method of paint removal:(a) Painting strategy selected in step 2.(b) Degree of surface preparation required by the maintenance system.(c) Amount of work to be performed and productivity requirements.(d) Size, configuration and accessibility of the structure.(e) Cost.

Paint removal methods are categorized into four groups based upon the level and type ofpaint emissions generated. These categories are:

(a) Emission Category 1 (Very High Emission Potential) Dry abrasive blast cleaningwith expendable or recyclable abrasives is in this category as it produces moredust than any other method of paint removal. The use of recyclable abrasivessignificantly reduces the volume of blasting debris that in most instances must betreated as a hazardous waste. Dry abrasive blast cleaning is the most effectivemethod of surface preparation for paint durability, and it has a high productionrate.

(b) Emission Category 2 (High Emission Potential) Wet abrasive blast cleaning andwater blasting are in this category. It is a dust free method of surfacepreparation; however, the wet blasting debris is more difficult to handle andtransport than dry debris. It requires the use of inhibitors to avoid flash rusting,and it is significantly slower than dry abrasive blast cleaning.

(c) Emission Category 3 (Moderate Emission Potential) Power Tool Cleaning withoutvacuum attachments and Chemical Removal are in this category. Power ToolCleaning produces significantly less dust and debris than dry abrasive blastcleaning. It is significantly less effective for paint durability than abrasive blastcleaning, and it has a medium production rate. Chemical Removal is a dust freeoperation, and the volume of debris is significantly less than abrasive blast

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cleaning. It is not a recognized method of surface preparation and pretreatmentof metal surfaces prior to protective coating; thus, further surface preparation isrequired before painting.

(d) Emission Category 4 (Low Emission Potential) Hand Tool Cleaning and PowerTool Cleaning with vacuum attachments are in this category as dust generation isminimal, and the volume of debris is significantly less than abrasive blastcleaning. Hand tool cleaning is the least effective method of surface preparationfor paint durability, and it has a low production rate.

The selected paint removal method emission category has an influence on selection ofcontainment as does the control level for emissions determined in step 4. Thecontainment system components capable of achieving Levels A, B and C of emissioncontrol for each of the emission categories are described in Appendix A.

At the completion of this step, if the method of removal and containment selected for theproject do not appear to be feasible, the painting strategy chosen in step 3 should bereconsidered.

Step 6 Selection of monitoring procedures

Project monitoring of emissions is performed to ensure adequate controls are in place toprotect the environment, the public and other workers in the vicinity of paint removal. Itshould include air quality, ground (soil) and water and sediment monitoring.

Air quality monitoring requirements may range from simple visual monitoring to elaborateinstrumental monitoring depending upon the location of the structure and method of paintremoval. Visual monitoring of dust emissions from containment or equipment duringsurface preparation and clean up is a subjective means of assessing whether the intendedlevel of control of emissions from these operations is being achieved while instrumentalmonitoring that enables a determination of the actual amount of lead as particulate matterin the atmosphere is an objective means of making this assessment. Appendix Bdescribes a method for instrumental monitoring of air quality.

Ground monitoring also may range from simple visual monitoring upon project completionto ensure all visible surface preparation debris has been removed from the work site toelaborate soil sampling and laboratory analysis of soil samples for lead prior to projectstart up and upon project completion to determine whether remediation is required orverify adequacy of project controls depending upon the location of the structure andmethod of paint removal. Appendix C describes a method for ground sampling andanalysis.

Water and sediment monitoring entails laboratory analysis of water and sediment samplesprior to project start up and upon its completion to determine whether the water orsediment has been contaminated by removal of the lead-containing paint. It is used todetermine whether remediation is required or verify adequacy of project emission controls.It is not used as a process control measure unless the project is near a drinking waterintake. In which instance, sampling and analysis should be carried out as arranged withthe Water Authority. Appendix D describes a method for water/sediment sampling andanalysis.

The methods, frequency and duration of monitoring are dependent upon the emissionspotential of the removal method, potential public health risk, potential adjacent workerhealth risk and potential environmental impact risk. The greater the potential health andenvironmental risks and the higher the emissions potential, the greater is the need formonitoring.

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Step 7 Establishment of worker protection measures

All personnel on the project who are exposed to lead paint removal should be adequatelyprotected to avoid inhalation or ingestion of lead paint and precautions should be taken toprevent them from inadvertently carrying lead containing dust or debris from the work siteto domestic or public locations where it continues to present a health hazard. Allmeasures adopted shall comply with governing legislation.

As the exposure standard for lead is 150 µg/m3

of air, it is necessary to determine thatemployees on the project are exposed to this or a higher level of lead during the courseof paint removal and collection of debris for disposal and implement appropriate controlmeasures. This determination may be made by evaluating monitoring data acquired onsimilar projects or monitoring the personal breathing zones of exposed workers at thebeginning of the project.

The following control measures are available to limit exposure to lead

(a) isolation of the work area(b) engineering devices(c) safe work practices(d) administrative practices.

Respirators are required whenever the concentration of lead is at or above the exposurestandard. Respiratory protective devices shall comply with AS 1716,and their selection,use and maintenance shall be carried out in accordance with AS 1715.

Protective clothing and equipment, housekeeping procedures, hygiene facilities, medicalsurveillance and employee training requirements specified in regulations shall be strictlyobserved.

Large, complex projects may warrant a written compliance program implemented andmaintained by an individual who is capable of identifying hazards and authorized to takeprompt corrective measures to eliminate them.

Step 8 Establishment of handling procedures

Debris generated during the removal of lead-containing paint should be collected in sucha manner that its release into the surrounding environment is minimized, placed in sound,suitable containers marked "hazardous waste" and stored on site so as to minimizecontainer corrosion and damage.

A representative sample of the debris should be analysed for lead in accordance with USEPA Method 1311 Toxicity Characteristic Leaching Procedure (TCLP). If the lead contentis less than 5 ppm, the debris is classified as non-hazardous waste, re-marked "non-hazardous waste" and disposed of in accordance with statutory regulations. If the leadcontent is 5 ppm or more, the debris is classified hazardous retaining its "hazardouswaste" marking and disposed of in accordance with statutory regulations.

Step 9 Establishment of work site cleaning requirements

The worksite should be returned to the condition that existed prior to starting work.

There should be no visual evidence of paint removal debris on the structure or itssurrounding environment.

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Reusable equipment should be cleaned in such a manner that release of paint removaldebris to the surrounding environment is minimized and it shows no visual evidence ofpaint removal debris at the time of its removal from the work site.

Consumable materials shall be disposed of in accordance with statutory regulations.

Step 10 Estimation of project cost

Having completed a preliminary project design by working through steps 1-9, an estimateof project cost should be prepared. If the cost is outside budget constraints, projectreassessment should be undertaken by working through steps 2-9 again and repeatingthe process until cost is within budget.

Step 11 Preparation of project specification

A project specification should be prepared that clearly addresses the issues of worker andpublic health and environmental pollution as well as surface preparation and painting.

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Bridge Repair Manual

Appendix B1Containment

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B1-1 Scope

This Appendix provides information on containment systems used for controllingemissions during the course of lead paint removal.

B1-2 General

Containment system components capable of achieving these levels of emission control foreach paint removal emission category are shown in Table B1. Emission control level A isa high level of control where only minimal emissions are allowed, B is a moderate level ofcontrol where limited emissions are allowed and C is a low level of control where limitedemissions are allowed.

B1-3 Containment system components

B1-3.1 Description

The components that comprise the containment/cocoon are described in B1-3.2-B1-3.6 below.

B1-3.2 Containment material rigidity

B1-3.2.1 General

The materials used to construct the shell of the containment cocoon and groundcovers can be either rigid or flexible. The rigidity or flexibility of the materials hasno bearing on the ability of the containment enclosure to control emissions.Selection of the material is based primarily on the need for long term durabilityand ease of construction.

B1-3.2.2 Rigid containment materials

Rigid containment materials consist of solid panels of plywood, aluminium, rigidmetal, plastic, fibreglass, or composites. Fire retardance of the materials shouldbe considered during selection.

B1-3.2.3 Flexible materials

Flexible containment materials consist of screens, tarpaulins, drapes, plasticsheeting, or similar materials. Fire retardance should be considered duringselection.

B1-3.3 Containment material permeability/resistance

B1-3.3.1 General

The permeability of the containment materials to air, water or chemicals willinfluence the degree of control over emissions that can be achieved. Thematerials should also be resistant to the media used for paint removal.

B1-3.3.2 Air impermeable materials

Air impermeable materials are those that are impervious to dust or wind, such asrigid panels or coated solid tarps, drapes or plastic sheeting. These materials willstop the passage of debris and essentially any air.

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B1-3.3.3 Air permeable materials

Air permeable materials are those that are formed or woven to allow air flow, butcan retain much of the larger airborne particulate.

These materials are commonly termed 'wind screens'. Because of theconstruction of the material, some dust will escape when using methods ofremoval that produce very high emissions such as abrasive blast cleaning.

B1-3.3.4 Water Impermeable materials

Water impermeable materials are any materials that are capable of containingand controlling water when wet methods of preparation are utilized. Note thatwind screens hung vertically may satisfy this objective provided the horizontalareas of the containment where ponding or standing water might be present arefabricated from solid, impermeable materials.

B1-3.3.5 Chemical/Solvent resistant materials

Chemical/solvent resistant materials are those that are not disturbed or softenedby prolonged contact with chemical or solvent stripping solutions.

B1-3.4 Support Structure

B1-3.4.1 General

The structure used to support the containment materials is classified as eitherrigid or flexible. The support structure used has no bearing on the level ofemissions control achieved. Its importance lies in the long term durability of thestructure and in the flexibility of its construction.

B1-3.4.2 Rigid support structures

Rigid support structures consist of scaffolding and framing to that thecontainment materials are affixed to allow little to no movement of thecontainment cocoon.

B1-3.4.3 Flexible support structures

A flexible support structure incorporates cables, chains, or similar systems to thatthe containment materials are affixed. Flexible support structures allow somemovement of the containment.

B1-3.5 Containment Enclosure Joints

B1-3.5.1 General

The joints between containment materials and between the materials and thestructure being prepared are either fully or partially sealed. The sealing of thejoints has an impact on the degree of emissions control provided by thecontainment system.

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B1-3.5.2 Fully sealed joints

Fully sealed joints require that all mating surfaces, between containmentmaterials and between the containment cocoon and the structure being prepared,are completely sealed. Methods of sealing include taping, caulking, Velcro, andany other material capable of forming a continuous, impermeable seal.

B1-3.5.3 Partially sealed joints

Partially sealed joints involve the mating of materials of each other and to thestructure being prepared, where the structural soundness of the joint isconsidered but a continuous, impermeable seal is not created.

B1-3.6 Containment entryways

B1-3.6.1 General

Access to and from the containment may require elaborate controls to ensurethat emissions do not escape during worker use or during windy periods thatcould cause the entryway to open. Entrances vary in sophistication from theconstruction of airlocks to the use of open seams between containment materials.

B1-3.6.2 Airlock entryway

An airlock entryway involves a minimum of one stage that is fully sealed to thecontainment. One door connects the airlock to the containment with a separatedoor to the outside. Both doors of the airlock should not be opened at the sametime, otherwise emissions may escape. The ventilation system used for thecontainment, should maintain the airlock under negative pressure. The airlockshould be equipped with a HEPA vacuum to allow gross decontamination of dustand debris from worker clothing prior to exiting.

B1-3.6.3 Resealable door entryway

Resealable doorways involve the use of entry doors capable of being repeatedlyopened and resealed. Sealing mechanisms include the use of zippers, Velcroand other similar means.

B1-3.6.4 Overlapping door tarpaulin entryway

Overlapping door tarpaulins involve two or three overlapping tarpaulins. Thissystem may have a tendency to open under windy conditions or could disruptdesigned airflow patterns when a negative pressure ventilation system is utilized.

B1-3.6.5 Open seam entryway

Open seam entryways involve an entrance to the contained area through openseams between containment materials.

B1-4 Ventilation system components

B1-4.1 Purpose

The purpose of the ventilation is to control emissions into the environment and toprovide air flow through the containment enclosure to reduce worker exposures

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to lead. Control of emissions into the environment can be achieved by creating anegative pressure condition inside containment, such that if a breach in thecontainment cocoon occurs, air from outside of the containment will flow inwardpreventing dust from escaping.

B1-4.2 Ventilation design alternatives

The ventilation can involve the use of designed mechanical systems or naturalventilation. When a mechanical system is specified, a negative pressurecondition should be required along with filtration of the exhaust air.

B1-4.3 Mechanical ventilation system

The containment enclosure is ventilated by mechanical means to ensureadequate air movement is achieved to reduce worker exposures to lead and toenhance visibility.

The system should be designed for uniform air flow through the containment ineither a cross-draft or down-draft mode.

The exhaust system should be designed with properly distributed exhaustedports or plenums, adequately sized exhaust ductwork for proper transport velocityand adequately sized discharge fans. This will provide the necessary air velocitywithin the containment to overcome system static pressure and provide properlysized and distributed make-up air points.

Air movement through the containment when using abrasive blast cleaningshould result in at least–

(a) 39 m/min cross-draft.

(b) 18 m/min down-draft.

Negative pressure achieved when using mechanical ventilation can be confirmedthrough instrument monitoring. A minimum of 0.8mm water column relative toambient conditions should be maintained. Inclined manometers or magnehelicgauges can be used for these measurements. Negative pressure can also beconfirmed visually through the concave appearance of the containment structureor by the use of smoke bombs to verify an inward flow of air at breeches in thecontainment. When using visual means, care should be taken to account for theinfluence of winds on the concave appearance of the containment enclosure ascompared with that created by the ventilation system.

B1-4.4 Natural ventilation system

Natural ventilation does not utilize mechanical equipment for moving dust anddebris through the work area. It relies on natural air flow patterns through thecontainment.

B1-4.5 Exhaust air filtration

When utilizing mechanical ventilation systems, filtration of the exhaust air shouldbe specified, otherwise airborne particulate from within the containment will beexhausted directly into the ambient air.

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Filtration systems typically employ wet or dry dust collectors or bag houses.Filtration to 2.0 µm may be necessary if workers are continually in the immediatevicinity of the exhaust. For removal methods that produce very low emissions,dust socks on the exhaust fan may be sufficient.

If paint is applied within the same containment system, it may be necessary touse a pre-filter to prevent wet paint droplets from damaging the air filtrationsystem, or to exhaust the air through an alternative filtration system such as dustsocks.

B1-5 Methods of collecting debris

B1-5.1 Handling

The debris generated within containment can be conveyed manually, by gravityor mechanically. To reduce worker exposures to lead, non-manual handlingmeans should be utilized wherever feasible.

B1-5.2 Manual collection

Manual collection involves the use of equipment such as vacuums, brooms,magnetic brooms, brushes, shovels, wheel barrows, buckets or bucket loaders tophysically move the debris to a collection point. Because of the potential forincreased worker exposure when using most of the methods, the use of vacuumis preferred.

B1-5.3 Gravity collection

Gravity collection is used for overhead work where specially designed hoppers orfunnels allow the debris to fall by gravity into duct work that channels it to acollection or reclamation point. Workers typically do not handle or contact thedebris.

B1-5.4 Mechanical conveyance

Pneumatic equipment or mechanical augers in the containment floor may beused to automatically transport the debris for collection or reclamation. As withgravity conveyance, workers have little need to handle or contact the debris.

B1-6 Designing a containment system

Guidance on the design of containment systems is found in SSPC Guide 6I(CON) andSSPC93-02. The following job site and structural considerations should be taken intoaccount when designing a containment system:

(a) Type of structure.

(b) Load bearing capacity and integrity of the containment system and of thestructure.

(c) Size and elevation of structure.

(d) Location of structure.

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(e) Proximity to other buildings, structures, operating equipment and traffic. Tightconfines may not permit the construction of certain containment devices.

(f) Local wind conditions

(g) Requirements of regulating authorities

(h) Whether the structure is riveted or welded. On certain structures; the welding ofcontainment system brackets adjacent to riveted seams should be avoided.

B1-7 Containment criteria table

Table B1 shows the containment system components capable of achieving three levels ofemission control for each paint removal emission category. Level A is a high level ofcontrol where only minimal emissions are allowed, Level B is a moderate level of controlwhere limited emissions are allowed and Level C is a low level of control where limitedemissions are allowed.

Paint removal methods based upon the level and type of paint emissions generated arecategorized as follows:

(a) Emission Category 1 Very High Emission Potential -Dry abrasive blast cleaningwith recyclable or non-recyclable abrasive.

(b) Emission Category 2 High Emission Potential - Wet abrasive blast cleaning andwater blasting.

(c) Emission Category 3 Moderate Emission Potential - Power tool cleaning withoutvacuum attachments and chemical removal.

(d) Emission Category 4 Low Emission Potential - Power tool cleaning with vacuumattachments and hand tool cleaning.

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TABLE 1

EMISSION CONTROL CONTAINMENT CRITERIA FOR PAINT REMOVAL METHOD (1)

EmissionCategory

Emissioncontrol level (2)

Containmentmaterial rigidity

Containmentmaterial (3)permeability

Containmentsupport

structure

ContainmentMaterial Joints

Containmententryway

Ventilationsystem

required

Negativepressurerequired

Exhaustfiltrationrequired

A Rigid or flexible Impermeable Rigid or flexible Fully sealed Airlock resealable Mechanical Required Required

B Rigid or flexible Permeable orimpermeable Rigid or flexible Partially sealed Overlapping Natural Not required Not required

1

Very highemissionpotential C See Note 4 NA NA NA NA Natural Not required Not required

A Rigid or flexible Impermeable Rigid or flexible Fully sealed Resealable oroverlapping Mechanical Required Required

B Rigid or flexible Permeable orimpermeable Rigid or flexible Partially sealed Overlapping Natural Not required Not required

2

High

emissionpotential

C See Note 4 NA NA NA NA Natural Not required Not required

A Rigid or flexible Impermeable Rigid or flexible Fully sealed Resealable oroverlapping Mechanical Required Required

B Rigid or flexible Permeable orimpermeable Rigid or flexible Partially sealed Overlapping or

open seam Natural Not required Not required

3

Moderateemissionpotential C See Note 4 NA NA NA NA Natural Not required Not required

4 A See Note 4 NA NA NA NA Natural Not required Not required

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B See Note 4 NA NA NA NA Natural Not required Not required

Low

emissionpotential

C See Note 4 NA NA NA NA Natural Not required Not required

NOTES:1. This guide is prepared for information only. It does not guarantee that specific controls over emissions will occur. Other combinations of

materials may provide controls over emissions equivalent to or greater than those combinations shown in the table.

2. Emission control Level A provides a high level of control, Level B a moderate level of control and Level C a low level of control.

3. Permeability addresses both air and water. Ground covers should be impermeable and of sufficient strength to withstand the impact and weightof the abrasive and equipment that might be used for cleaning or reclamation. Ground covers may also extend beyond the containmentboundary in order to capture debris that may escape. When chemicals are used, the containment materials should be resistant to both chemicalsand water.

4. Impermeable ground covers and free hanging tarps are sufficient to control emissions.

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Bridge Repair Manual

Appendix B-2Air Quality Monitoring

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B2-1 Scope

This appendix describes a method for monitoring ambient air quality in the vicinity of paintremoval operations. It enables the determination of the actual amount of lead asparticulate matter in the atmosphere utilizing sampling equipment.

B2-2 General

The purpose of air quality monitoring is to assess whether the health of the public ornearby workers is being endangered by lead or respirable emissions from the work site.

B2-3 Instrumental monitoring of TSP lead

B2-3.1 Principle

Sampling monitors are located at appropriate places around the work site.Preliminary monitoring is performed to establish background levels ofcontaminants before the removal/repair project commences, and uponcommencement of operations, monitoring of the work site is undertaken.

B2-3.2 Materials and equipment

High volume air sampling equipment -equipped with a total suspended particulate(TSP) collection head.Equipment filters - one for each monitor for each period of operation.Electrical supply - 240 V or an appropriately sized generator.Wind direction and velocity indicators.

B2-3.3 Monitor sitingB2-3.3.1 General

The selection of monitor placement locations is dependent upon a number of siteconditions, including but not limited to:

(a) surrounding topography;(b) variability in wind direction;(c) proximity to obstacles such as building and trees;(d) proximity to other sources of emissions such as automobiles.

B2-3.3.2 Determination of prevailing winds

The prevailing winds may be determined by using Weather Bureau information ora portable weather station.

B2-3.3.3 Identification of a down-wind monitoring zone

Select a down-wind monitoring zone by constructing an arc 15° on both sides ofthe prevailing wind direction.

B2-3.3.4 Placement of Monitors

The recommended procedure is as follows:

(a) Position the monitors within the down-wind monitoring zone at adistance away from the structure based on its height as described

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below. Place additional monitors at high public risk receptors such asschools, homes, or hospitals, even if they are located outside of themonitoring zone to assure protection of the public from the inhalation ofairborne lead. Locations where the public is present should takeprecedence over the criteria presented below that is based on prevailingwind and distances.

(b) For structures less than 6 m in height, locate one monitoring stationwithin the down-wind monitoring zone, in the direct line of prevailingwinds, at a distance of approximately 3 times the height of the structure.Representative high risk areas located within 30 m of the structure,regardless of prevailing wind, should also be monitored.

(c) For structures from 6m to 30m in height, establish two monitoringlocations within the monitoring zone. One should be located along oneside of the monitoring zone (left side of the 15° arc to the left of theprevailing wind), at a distance equivalent to approximately twice theaverage working height on the structure. The second monitoring locationshould be positioned along the opposite side of the monitoring zone at adistance of approximately twice the total height of the structure.Representative, high risk areas that are located within a distance of 45m or three times the total height of the structure, whichever is greater,should also be monitored.

(d) For structures greater than 30 m in height, establish two monitoringlocations in the monitoring zone as described above, except that the firstlocation should be at a distance approximately equal to the averageworking height on the structure, and the second location should beestablished at a distance no greater than twice the average workingheight. Representative, high risk areas within 90 m or twice the height ofthe structure, whichever is greater, should also be monitored.

(e) Determine if monitoring locations need to be moved depending on theanalysis of results. If wind directions are found to vary, the monitoringlocations may require repositioning. When working many spans of abridge, the monitors may have to be relocated for each span.

B2-3.3.5 Baseline monitoring

Monitoring around the project site should be conducted for a minimum of three tofive days while no work activities are underway. If the monitoring demonstratesthat there is a high degree of variability in the background levels, upwindmonitoring at a remote location away from the influences of the project siteshould be utilized to track background levels on a daily basis.

The influence of the initial baseline date or the continual upwind monitoringshould be taken into consideration when analyzing the test results to establishthe contribution of the paint removal activities to the total amount of airborne leadproximate to the work-site e.g. due to the use of leaded petrol, an allowance of10 percent above the 80% confidence interval of the background level may be

used if it exceeds 1.5 ug/m3

.

B2-3.3.6 Work Site Monitoring

The extent and direction of work site monitoring is based on the potential healthrisk to the public and nearby workers.

Four options are available:

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(i) Full time monitoringMonitoring throughout the duration of the project should be employed ifthe public is present in the vicinity of the project for most of the time (e.g.homes, schools, hospitals are next to the project site), or other workersare nearby on a continual basis.

(ii) Start-up monitoringMonitoring at project start-up us used to establish the adequacy of thecontrols over emissions. Once it is established that the results areacceptable, the monitoring is discontinued. Monitoring may be resumedif suspect emissions occur or the method of removal and containment ischanged. This type of monitoring is used in areas where the public andother workers are present on an occasional basis.

(iii) Monitoring for complaintsPublic complaints or questions regarding emissions may trigger the needfor localized, short-term assessments. The disadvantage to thisapproach is that if the assessment shows that unacceptable emissionsare occurring, the impact of the emissions prior to monitoring may bequestioned and require resolution.

(iv) No monitoringProjects outside of public access or away from other workers who arenot involved in the project should not require monitoring.

B2-3.3.7 Operation of equipment

The high volume air samples should be operated and calibrated strictly inaccordance with governing legislation.

B2-3.4 Total suspended particulate matter

Total suspended particulate matter shall be determined in accordance with AS2724.3 andanalysed for lead content in accordance with governing legislation.

B2-3.5 Reporting/record keeping

The following should be recorded:

(a) Name and location of job site.(b) Date of monitoring.(c) Time of monitoring (Time monitoring begins and ends each day).(d) Identification serial number of monitoring units.(e) Description of specific monitor locations.(f) Description and location of operations underway at time of monitoring.(g) Wind direction and velocity.(h) Flow chart verifying the rate of airflow across the filter throughout the sampling.(i) Name and address of laboratory used.(j) Laboratory test procedure utilized.(k) Laboratory test results, expressed in ug/m

3.

(l) Names of person/firm conducting the monitoring work.

Copies of all records relating to ambient air monitoring should be maintained for the lengthof the project plus a minimum of three years.

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Bridge Repair Manual

Appendix B-3Ground (Soil) Monitoring

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B3-1 Scope

The Appendix provides a method for sampling and analysing the ground (soil) in thevicinity of a project prior to its start and upon its completion to determine if the ground hasbeen contaminated by lead from the work.

B3-2 Background

Pre-existing levels of lead in the ground can vary greatly within a few metres due to pastusage of the property and to uneven distribution of previously dislodged paint chips.Thus, while this Appendix provides means for collecting and analyzing samples, suchvariability should be recognized when analyzing the data.

B3-3 Materials and equipment

Sampling tool -for the collection of ground plugs approximately 20 mm in diameter and10 mm in depth.

Sample collection bags or containers - comprised of a material such as polyethylenethat will not contaminate the sample.

Tape measure and compass -to document the precise locations of the samples

Sampling template - 300 x 300 mm with a 25 mm hole in the centre.

Deionized water - to clean the sampling equipment.

B3-4.1 General

Sample site selection depends on the configuration and location of the structure. Theproject/structure should be subdivided into logical units for sampling. The ground aroundeach structure or a portion of a structure should be considered a unique structure forsampling and sampled separately.

B3-4.2 Site selection for structures less than 16m in height

One sample should be removed on each north, south, east and west compass point at adistance away from the structure equal to its height.

For long structures, an additional sample location should be selected for every 32msegment of length. If the structure crosses over ground, samples immediately beneaththe structure as described in

4.4 should be removed.

B3-4.3 Site selection for structures greater than 16 m in height

Two samples should be removed on each north, south, east and west compass point,oneat a distance away from the structure of 16m and the other at a distance away from thestructure equal to its height.

For long structures, an additional sample in each row should be selected for every 32 msegment of length. If the structure crosses over ground, samples immediately beneaththe structure as described in 4.4 should also be removed.

B3-4.4 Site selection for structures crossing ground

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If a structure crosses over the ground, a minimum of two samples should be removedfrom beneath each end. Additional samples should be collected in proportion to the floorarea of the structure, at arate of one additional sample for every 500 m

2of ground surface covered.

For elevated structures such as tanks, a minimum of two samples should be collectedbeneath the centre of the structure with additional samples removed in proportion to the'floor area' of the structure at arate of one additional sample for every 500 m

2of ground surface covered. Perimeter

sampling as described in B3-4.2 and B3-4.3 should be carried out.

B3-4.5 High risk receptors

Samples should be removed at high risk receptors such as schools, day care centres,occupied housing, and hospitals that are located in the vicinity of the work area if there isthe possibility that ground contamination from project activities could occur.

B3-5 Sample collection

A sample of the surface of the ground should be collected at each sample site. A sampleconsists of five plugs of ground collected at each location and combined in a singlecontainer to represent the sample at the specific site. The following sampling procedure isrecommended:

(a) Remove by hand visible chips of paint on the surface of the ground.

(b) Place a 300 mm x 300 mm template parallel or tangential to the structure.

(c) Remove circular surface plugs of ground, measuring approximately 20 mm indiameter and 10 mm in depth, from the centre of the template and at each of thefour corners. Place the five plugs in a single sample container. This representsone sample from one sample site. Clean the sampling tool with deionized waterprior to moving to a new sample site.

B3-6 Frequency of sampling

Samples are removed prior to project start-up and upon project completion. (Interimsampling may be carried out to determine the performance of the containment.)

The ground plugs should be analysed for lead in accordance with US EPA Method 3050or approved equivalent method.

B3-8 Interpretation of results

No paint chips or debris resulting from the removal operation should be visually evidentthroughout and around the project site. The ground will be considered to have beencontaminated by project activities under any of the following conditions:

(a) Visible debris is present.(b) If the mean pre-project level is less than 200 ppm, and an increase in total lead

content of 100 ppm or more occurs.

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(c) If the mean pre-project level is greater than 200 ppm, and the 80 percentconfidence level of the post project mean levels are more than 10 percent higherthan the 80 percent confidence level of the pre-project mean levels.

B3-9 Reporting/record keeping

The following information should be recorded:

(a) Name and location of job site.(b) Dates of sampling.(c) Visual evidence of contamination.(d) Specific location of samples sites (Direction and distance). The use of drawings

is recommended.(e) Name and address of laboratory.(f) Laboratory test method.(g) Laboratory test method.(h) Name of person/firm conducting the sampling.

Copies of all tests results shall be maintained for the length of the project plus a minimumof three years.

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Bridge Repair Manual

Appendix B-4Water and Sediment

Monitoring

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B4-1 Scope

This Appendix describes a method for sampling and analysing water and sediment prior tothe start of a project and upon its completion to determine if the water/sediment waspolluted by lead from the work.

B4-2 General

Sampling of surface water and sediment for lead to determine whether pollution hasoccurred is of value only in limited circumstances. In fast moving bodies of water, watersampling represents only transient water quality and adequate evaluation of results isdifficult. Similarly, in bodies of water greater than 4 m in depth, sediment sampling is oflittle value.

Water or sediment sampling may provide meaningful data for slow moving, shallow bodiesof water where drinking water intakes or sensitive environmental receptors such as oysterbeds are near the work site.

B4-3 Materials and equipment

Rigid container -with resealable lid, approximately 250 ml in capacity, for water orsediment samples.Stainless steel scoop - for collection of sediment samples.Sample collection bags or containers - of a material such as polyethylene that will notcontaminate the sample.Tape measure and compass -for documenting the precise sample locations.

B4-4 Number of samples

B4-4.1 Structures alongside a body of water

For work on tanks, buildings, or structures located next to a body of water, soilstests should be used in lieu of water or sediment testing.

If soil is not present and water/sediment sampling is required, for every 30msegment of the structure, one sample of water and one sample of sediment at theshore line, and one additional set of samples 6m from the shore line should betaken.

B4-4.2 Structures less than 150m in length that pass over a body of water

The sampling plan should include the following if water/sediment sampling isrequired:

(a) If the maximum height of the work area is less than 15m above the waterfor every 30m in length, or portion thereof:(i) Collect two water samples at a distance downstream that is no

further than the equivalent of the height of the structure.(ii) Collect sediment samples beneath the structure at a frequency

equivalent to one sample for every 500m2

of water areacovered by the structure.

(b) If the maximum height of the work area is greater than 15m above thewater, for every 30m length or portion thereof:(i) Collect one water sample downstream within 10 m of the

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structure and a second at a distance downstream no greaterthan the average height of the structure.

(ii) Collect sediment samples immediately beneath the structure at

a frequency equivalent to one sample for every 500m2

of waterarea covered by the structure.

B4-4.3 Structures greater than 150m in length that pass over a body of water

The sampling plan should include the following if water/sediment sampling isrequired.

(a) If the maximum height of the work area is greater than 15m above thewater, for every 150m length or portion thereof:(i) Collect two water samples at a distance downstream that is no

further than the equivalent of the height of the structure.(ii) Collect sediment samples immediately beneath the structure at

a frequency equivalent to one sample for every 500m2

of waterarea covered by the structure.

(b) I f the maximum height of the work area is greater than 15m above thewater, for every 150m length or portion thereof:(i) Collect one water sample downstream within 10m of the

structure and a second at a distance downstream no greaterthan the average height of the structure.

(ii) Collect sediment samples immediately beneath the structure at

a frequency equivalent to one sample for every 500m2

of waterarea covered by the structure.

Where sensitive receptors such as drinking water intakes or oyster beds arelocated in slow moving shallow bodies of water downstream within 50m of thework site, it may be prudent to collect sufficient water samples to characterise thearea.

B4-5 Sample collection procedure

B4-5.1 Collection of water samples

Dip or grab samples should be collected. The recommended procedure is asfollows:

(a) Place the container just beneath the surface of the water and pull in anupstream direction to collect the sample.

(b) Collect approximately 250ml of water, seal the container, and tape itshut to avoid spilling the contents or tampering.

(c) Use a separate, clean container for each sample.

B4-5.2 Collection of sediment samples

Scoop samples should be collected. The recommended procedure is as follows:

(a) Scooping in an upstream direction to a maximum depth of 100mm,collect approximately 250ml of sediment, seal the container and tapeshut to avoid spilling the contents or tampering.

B4-6 Frequency of sampling

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Samples should be taken prior to project start-up and upon project completion. (Interimsampling may be carried out to assess the performance of the containment during thecourse of the project.)

B4-7 Laboratory analysisThe samples should be analysed for lead in accordance with US EPA Method 3050 orapproved equivalent.

B4-8 Interpretation of results

Paint chips or debris shall not be visually evident in the water or sediment.

Water is considered to have been contaminated by the project activities under either ofthe following conditions:

(a) The mean pre-project level is less than 3.5µg/L and an increase in the mean leadcontent of 1.5µg/L occurs.

(b) The mean pre-project level is greater than 3.5µg/L and the 80 percent confidencelevel of the post project mean levels is more than 10 percent higher than the 80percent confidence level of the pre-project mean levels.

Underwater sediment is considered to have been contaminated by the project activities ifthe 80 percent confidence level of the post project mean levels is more than 10 percenthigher than the 80 percent confidence level of the pre-project mean levels.

B4-9 Reporting/record keeping

Copies of all test results should be maintained for the length of the project plus a minimumof three years.

The following documentation should be provided:

(a) Name and location of job site.(b) Dates of sampling(c) Specific location of sample sites (The use of drawings is recommended).(d) Name and address of laboratory.(e) Laboratory test method.(f) Laboratory test results expressed in ppm.(g) Name of person/firm conducting the sampling.

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Bridge Repair Manual

Appendix CGuidelines for welding

old steels

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C1. Background/introduction

The materials used in railway construction over the past 100 years or so have evolvedmore or less in step with the changes in the metal fabricating industry and it is important tokeep in mind that for the first two thirds of this period welding was not widely used andriveting was the usual method of joining. As a consequence of this the weldability of thematerials involved was not a prime consideration and the ease, and in some cases thepracticability, of welding can vary considerably. This, of course, makes maintenance verymuch more complex as riveting is no longer commonly used and where welding is notpracticable bolting may be the best solution.

In an actual repair situation it is clear that identification of the material involved is the firstand most important step.

It is hoped that in time this information will be available for all bridges in the system.

C2. Wrought and cast iron

It is appropriate to describe in a short paragraph the differences between wrought andcast iron since, unfortunately, the terminology in common use in Australia does notcorrespond to the engineering definitions of wrought and cast iron.

Cast iron is a product of a blast furnace with a high carbon content (see Table 1) usefulonly in compression. Since it has almost no ductility in tension, its use is confined tocompression situations, i.e. bridge columns, compression side of beams, and tunnelliners. The cast iron discussed in this note should not be confused with the modernspheroidal graphite iron that has good tensile properties but poor weldability.

The cast iron covered here is the type often described as "Grey Cast Iron".

Wrought iron, as we shall consider it, was produced by "puddling" pig iron on contact withmill scale (iron oxide) and is similar to a low carbon low strength mild steel containing slaginclusions that reduce its properties in the through thickness or "Z" direction. Beams ofriveted construction often had cast iron in the compression flange and wrought ironelsewhere. Beams of this type have been seen in the central city tunnels.

Wrought iron is quite easily welded if the provisions described below are observed, butgrey cast iron is quite a different proposition and may be either very difficult or impossibleto weld.

It is therefore very important to identify the materials involved before any repair work isundertaken.

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Table C1Iron based structural materials - Typical properties

Cast iron Wrought iron Mild steel Structural Steel

Carbon 3.5% 0.1% 0.1 to 0.3% 0.18%

Silicon 1.9% 0.2% 0.3% 0.2%

Sulphur 0.1% 0.1% 0.06% 0.02%

Phosphorous 1.0% 0.1% 0.06% 0.25

Manganese 0.7% 0.4% 0.4% 1.0%

Slag 0 1% 0 0

Yield Stress - 215 MPa 250 Mpa 250 Mpa(Specified Min)

Tensile Stress 120 MPa 354 MPa 460 MPa 410 Mpa(Specified Min)

Elongation - 30% 20% 22%(Specified Min)

C3. Welding wrought iron

Since the carbon and sulphur contents of wrought iron are low, it presents no weldabilityproblems in terms of hot or cold cracking, but the presence of slag stringers aligned withthe forging direction presents the only problems. Firstly, whilst butt welds in the X and Ydirections are quite feasible, welds on the surface Z direction are not recommended ifsignificant load is to be transmitted as a lamellar tearing type of fracture is likely to occur.

Welding by the MMAW method is usually recommended using Basic Low Hydrogenelectrodes. Not that hydrogen is a concern, but the basic flux is better able toaccommodate the slag absorbed into the weld pool. Neither preheat nor post heat isrequired. Welding procedures and preparations are similar to those used for structuralsteel but it is recommended that welding speeds be reduced to 5066% of those used forsteel to allow time for slag removal from the weld pool.

Welding procedures and operators should be qualified where possible along the lines ofqualification to AS 1544 Pt 1. If wrought iron of suitable section is not available,qualification may be done using Grade 250 structural plate.Where distortion due to welding is undesirable, then the welding procedure may becombined with a peening procedure to eliminate distortion. See WTIA TN11 for details ofthis procedure.

In cases where it is necessary to make a connection to the surface of a wrought ironmember then consideration should be given to replacing a length of the wrought iron bystructural steel attached by butt welds to wrought iron or by using a bolting technique.

C4. Mild steel

Mild steel was first produced in the late 1800's as a cheaper substitute for wrought ironthat was rather expensive and variable in properties. The differences between wroughtiron, mild steel and the current structural steels can be seen in Table 1. The important

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things to note are the higher carbon content, relatively high sulphur and phosphorouscontents and the low manganese content.

Wrought iron is readily forge or blacksmith welded, but mild steel does not lend itself tothese welding processes and the introduction of mild steel led to a great increase inriveting and the extinction of forge welding.

Fusion welding of mild steel faces two problems. Firstly, the higher carbon content, whichincreases the hardenability of the material and requires higher levels of preheat and arcenergy to prevent excessive hardening in the HAZ which can be dealt with; but moreimportantly the tendency towards hot cracking in the HAZ arising from the low manganeseto sulphur ratio. (Compare the values in Table 1 for Mild Steel and Structural Steel.) Whilstsome compensation for this problem is possible by adjusting the welding procedure, thefusion welding of some mild steels is impracticable. An additional factor is that mild steelsare frequently segregated, that is, contain bands of high carbon/sulphur content and theseareas are likely to cause welding problems.

Whether a particular piece of steel is likely to be difficult to weld depends very much uponthe raw materials used in steelmaking and is therefore at the current time very much anunknown. The safest course is to either avoid welding or to extract a small sample ofmaterial for chemical analysis and metallographic examination as will be described later.

As with wrought iron and structural steel, both the welder and welding procedure shouldbe qualified prior to commencement of work. Again the qualification procedure describedin AS 1554 Pt 1 should be followed. Since the mild steels are the most difficult of the threematerials being discussed, welder qualification on a mild steel should be accepted asqualification for procedures within the limits allowed by AS 1554 for wrought iron andstructural steel.

C5. Welding procedures for mild steel

Irrespective of the results of chemical analysis, mild steels should be regarded as being atleast Weldability Group Number 5 since the sample removed for analysis and the modernanalytical methods test only a small area and may not detect segregated areas.

To minimise the risk of HAZ hot cracking, weld beads should be kept small and ifnecessary buttering techniques should be used to reduce the residual stress from weldingand the chance of cracking. Low hydrogen basic consumables must be used to counteractthe deleterious effects of sulphur and phosphorous into the weld metal.

For those reasons, MMAW basic low hydrogen is the only welding process really suitablefor welding these materials. Other welding methods have either too large a HAZ and hotcracking risk, or low tolerance to sulphur and phosphorous absorption to yield satisfactoryresults.

C6. Structural steel

Structural steel was developed to overcome the shortcomings of mild steel, i.e. coldcracking, hot cracking, brittle fracture and lamellar tearing. Whilst these matters are tooextensive to describe here, the structural steels are characterised by low carbon, sulphurand phosphorous contents, low inclusion contents and small grain size and, in Australianmade steels, correspond to AS 1204 and AS 3678. Such steels are intended for weldingand avoid the problems of cold and hot cracking and, in Australian made steels, thepossibility of lamellar tearing.

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The procedures for welding such steels are fully described in AS 1554 and the welder andprocedure requirements of this standard should be observed fully. Welding consumablesshould as far as possible conform to the prequalified consumables listed in Table 4.5.1(A)of AS 1554 and in repair situations it will generally be found that adherence to theprequalified preparations of Table 4.4(A) will provide the optimum solution.

C7. Weld quality

The quality of the completed weld should be confirmed by visual and non destructivetesting. Welds in major members should comply with AS 1554 Pt 5 Section 6 and welds insecondary members to AS 1554 Pt 1 Section 6.

C8. Quality of repairs

Generally, only visual, magnetic particle and ultrasonic examination will be feasible onbridge repairs, but radiographic testing should be used in place of ultrasonic testing wheregeometry permits and on qualification tests.

C9. Recording of repairs carried out

A record should be made of each repair carried out and should include at least thefollowing information:

Bridge identificationNature of damageLocation and date of samples removed for material identificationMetallurgical report number and date.Detailed description of defect with photograph if possible.Selected repair method.Welding procedures together with a copy of WPS and WPQ.Welders used together with qualifications and date.Material used, i.e. plate numbers and consumable batch numbers.Repair date.Visual and NDT test reports.Photograph of completed repair (if possible)Materials used plates etc, welding consumables, paint and manhours.Time and date bridge returned to normal service.

Such records should be kept by the Corridor Manager or nominated representative

C10. Material Identification

As discussed above, it is essential before embarking upon any form of welding repair todetermine the nature of the materials involved. This can be done from existing records ofconstruction, although care is necessary if previous repairs have been carried out on thebridge; from material identification marks on rolled sections that often give the name of thesteelmaker and material standard; and by metallurgical examination of the steels involved.

Removal of a sample for examination should be done for each piece of plate or sectioninvolved in the welded repair, preferably in a location where rewelding is not required, andsimply grinding smooth the area of material removed is acceptable. Typically notching aV-shaped section from the edge of a plate or section approximately 15 mm wide, half-plate thickness and 20 mm long will suffice. Removal is best done by hand using ahacksaw as power grinders often overheat a small sample. An alternative method that isquicker and better is to take a core sample using a trepanning cutter. The sample should

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be min 15mm diameter. Samples should be sealed in an envelope clearly marked withbridge identification and sample location and sent to a laboratory for metallographicexamination and chemical analysis for carbon, manganese, silicon, aluminium, sulphurand phosphorus contents.

Occasionally it may be impossible to remove a sample for the above testing by a simplesawing method. In such cases the use of a "Boat Sample" removal apparatus can beconsidered, or the use of in situ metallography. In the latter case the metal surface isprepared without metal removal to permit microscopic examination on site or after theremoval of a surface replica.

Unfortunately, the current methods of in situ chemical analysis, spectrographic and X-raydiffraction, are not suitable for some of the elements of interest and it may be necessary toremove drillings for chemical analysis. In this case care must, of course, be taken toensure that the drillings removed are not contaminated with paint, oil or other drillinglubricant. Sample drillings should be sealed in an envelope marked with bridgeidentification and sample location.

Usually about 30gm of drillings will be required for chemical analysis and this represents a8 mm dia hole of about 8-10 mm in depth that will provide the necessary sample and willnot require welding repair.

C11. Identification of Wrought Iron

Identification of wrought iron bridges is very important, so that over estimation of ratedcapacity and remaining fatigue life does not occur, because they are assumed to be steel.This has been a common mistake. In one case, the same underbridge was assessed on4 different occasions by 3 different groups and all assumed the underbridge to be steel,when it was actually wrought iron.Steel structures which have some wrought iron components are particularly difficult toidentify. Drawing prints for the Murwillumbah Line trusses at Lismore, Woodlawn, Eltham,Booyong and Stokers Siding state that the trusses are steel with wrought iron componentscoloured blue (approach plate web deck spans are wrought iron) but as the originaldrawings are not available, the wrought iron components of the truss can not be identifiedfrom the drawings.

Office Identification of Wrought Iron

Historical Records

Office identification of wrought iron should be based on historical documents recording theconstruction date of the bridge. Advice may be sought from the Structures Officer or theStructures Examiner, particularly if a dated plaque is on the bridge.

Note: Do not rely on the date on drawings unless you have additional confirmation. Twounderbridges were assessed as steel because of the date on the drawing. The drawinghad in small print “TAKEN FROM FIELD MEASUREMENTS”and the signatures were copies. The drawing had been prepared from field measurements as the original drawingwas lost. It had been assumed that the underbridges had been constructed at the time ofelectrification, which coincided with the drawing date, instead of the date of construction ofthe line.

Design Details

Design details are another indicator that a bridge may be from the wrought iron era. Itmust be emphasised that these details can exist in either steel or wrought iron bridges,

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but they at least indicate further assessment needs to be made. The design details are asfollows:

i. Flat bar tension members, particularly if they are diagonal tension members.ii. Tie rods with turnbuckles for tensioning and pin connections used for wind

bracing and/or diagonal tension members.iii. Wind bracing or sway bracing which includes:iv. Flat bar membersv. Connections to girders made by forge bending and/or forge welding of bracing

members instead of using gusset plates.vi. Connection of wind bracing to the centre of web (ie mid-depth) and/or away from

stiffeners.vii. Angles which have chamfered edges on both sides of the toes (steel angles are

rounded on the inside face and square on the outside).viii. Expansion bearing of simple plate on plate design instead roller bearings for

spans above 20 metres long.ix. Rivets with flattened or cone shaped heads instead of round heads.

Field Identification of Wrought Iron

Test Samples

The most positive method of field identification is to obtain core or other samples formetallurgical assessment by preparing macros or micrographs as detailed above, todetermine if laminations exist. For an as constructed underbridge one sample may besufficient. For most underbridges over 100 years old there is usually strengthening and/orrepairs which have added steel plates and sections. In this case, a number of sampleswill be required.

Magnetic Particle Testing of Edges

Taking and testing samples is a costly and time consuming process. A simpler methodhas been field trialed on a number of underbridges of both wrought iron and steel. Thismethod involves filing or grinding an edge, then magnetic particle testing the edge to seeif laminations can be seen which indicate wrought iron. Care has to be taken as earlysteel may have stringer inclusions that look like laminations. Some problems were foundwith early steels during the field trials, but removing more metal by filing usually gave amore definite result (figs C.2 to C.5).

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C12. Welding process

Increasing temperature and welding on a member under stress can result in collapse ofthe structure or excessive distortion of a member. AS 1554 in Par 5.7.2 indicates thatsuch welding is not permitted unless the question is discussed with the relevantauthorities and safety precautions are taken. AWS D1.1 is a little more specific in Par11.5.2 that sets a limit of 20.7 MPA on members to be repaired. It will therefore benecessary to unload the area to be repaired by the use of appropriate falsework beforewelding repairs are undertaken in most circumstances.

It is important that all involved with bridge repair be made aware that, whilst welding offersa quick and convenient joining method, unless used very carefully, it can seriously reducethe safety of a structure such as a rail bridge by increasing the danger of fatigue cracking,brittle fracture, and in some cases lamellar tearing.

Compared with bolting or riveting, welding carries with it a number of problems. Firstly ina bolted or riveted structure, the failure of a single member by brittle fracture or fatiguefailure is often confined to that member, but in a welded structure the failure will oftenpropagate through the weld to the next member. This was the cause of the numeroussinkings of welded ships during and after World War II when welding was first widely usedin ship construction.

Secondly, in fusion welding a region of the HAZ adjacent to the weld is always overheatedand in metallurgical terminology "burnt". This burnt region is an incipient crack and isusually regarded as a continuous crack 0.2 mm deep for fracture mechanic calculations.It is therefore clear that replacing riveting or bolting by welding results in a structure verymuch weaker in fatigue unless the burnt region at the weld toe is ground out. Forexample, AS 4100 gives a bolted flange a rating of 140 MPA whilst a welded flange ofsimilar design is rated 63 MPA.

Thirdly, welding used in a repair situation produces both distortion and areas of hightensile residual stress that can seriously reduce the fatigue resistance of a structure. It isalmost always futile to simply weld up a fatigue crack or even to use a short doubling plateover the cracked area since rapid recurrence of cracking is inevitable.

Finally, it must always be borne in mind that the bridges of concern were built before theadvent of fusion welding and their materials of construction are often not readily amenableto this welding method.

C12.1 Weld Surface Condition

Where fatigue cracking is a problem and in some circumstances where brittlefracture could occur, the weld surface profile has a considerable effect on theservice life of the joint. For the purpose of this manual we shall simplify the rangeof surface conditions as follows:

a) As weldedb) weld toe groundc) weld surface fully ground.

There are other weld surface treatments that offer even greater improvements inperformance than b) or c) above but these are probably not required for bridgerepairs and will not be discussed further.

C12.2 Weld Toe Grinding

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As described above any fusion weld in steel or wrought iron contains a virtualcrack the full length of the weld toe of around 0.2 mm in depth and the removal ofthis zone by disk grinding or better still by use of a tungsten carbide burr in apneumatic pencil grinder will increase the allowable fatigue stress by around40%. The depth of grinding must be at least 0.5 mm but should not result in theloss of more than 10% of plate thickness.

This procedure requires around 1 man hour/m and is strongly recommended forall repairs on lower flanges. A similar result at lower cost can be achieved bydisk grinding but this requires rather more skill on the part of the operator and itmay be difficult to achieve a satisfactory result in a bridge repair situation.

C12.3 Full Weld Surface Grinding

Complete grinding of the weld surface and toe will yield an improvement of about50% in fatigue performance whilst polishing of the weld surface by burr grindingyields about 80% improvement, but these are expensive and time consumingprocesses not generally justified on bridges.

The desirable level of weld surface depends naturally upon the stress situation atthe repair location. As guidance it is proposed that if Design Branch has notspecified other requirements the following be used:

a) Transverse welds on lower flange. Weld toe ground as above. Othercriteria as per Table 6.1 in AS 1544 Pt 5.

b) Longitudinal welds on lower flange and other welds below _ web height asper Table 6.1 of As 1554 Pt 5.

c) Other welds as per Table 6.2 of AS 1554 Pt 1.

Where NDT is carried out, the requirements for cases a) and b) shall be Table6.2 in AS 1554 Pt 5 and in case c) Table 6.3 in AS 1554 Pt 1.

C12.4 Weld Processes and Consumables

Usually repair welds are best carried out using the Manual Metal Arc processsince this offers a good combination of flexibility and weld metal properties.However, where extensive welding is required the advantages of higherproductivity offered by the continuous wire welding processes should beconsidered.

The continuous wire processes are either flux or gas shielded or self shieldedcored wire.

Flux shielding, i.e. submerged arc welding, is generally only used in thedownhand and horizontal/vertical positions, although with special equipment itcan be used in the horizontal position. Gas shielded processes, i.e. MIG, GMAand TIG are usually difficult to us in a field repair situation because it isnecessary to provide a shelter to prevent the wind upsetting the gas shield.

The self shielded cored wire process is very much more suited to a field repairsituation since it is largely immune to the effects of wind and offers excellentproductivity and surface profile. Acceptable consumables should meet therequirements of AS 2203.1 W40 or W50 grades.

Manual metal arc electrodes should be of the basic low hydrogen type to provide

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the required resistance to HAZ hydrogen cracking in steels of low weldability,good weld metal notch toughness and tolerance to the slag stringer pick up whenwelding wrought iron. In a repair situation it is best to choose electrodes with 1)low yield strength, 2) good weld metal toughness, 3) smooth runningcharacteristics, and 4) that are supplied in a moisture proof package.

Specific electrodes from different local manufacturers that can be recommendedare Cigweld Ferrocraft 61 LT (for reason 1), WIA Austarc 16TC (for reason 3) orLincoln Jetweld LH-70 (for reasons 2 and 4). It is usually better to use theelectrodes familiar to the welder rather than retrain a welder to use an unfamiliarconsumable type. Electrodes should only be used if in good condition, i.e. nocore wire rusting coating, flaking or laitance and after baking in accordance withthe maker's recommendations or those given in WTIA Tn 3.

C12.5 Minimum Weld Size

It is important to ensure that the weld size deposited is not less than the valuesgiven in AS 1554 Pt 1 Table 3.3.5. During welding it is as well to check that thewelding current and travel speed are in accordance with the approved weldingprocedure. Welding current is best measured by a clamp meter since the meterson welding equipment are seldom reliable. Failing this, the measured size of afillet weld will usually allow a good estimate of the welding conditions used. SeeWTIA Tn 1 Fig 7.

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Bridge Repair Manual

Appendix DTechniques for removing

rivets using oxy-fuelequipment

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Procedure for rivet removal

Option A

Using oxy-acetylene or LPG (LPG preferred option).

For plate thickness combinations of 0mm to 40mm.

1. Adjust torch to a neutral flame, using a large gouger.48 GB Type 44 or 4164 GB Type 44 or 41

2. Heat head of rivet to required temperature (melting point), ensuring no heatapplication to adjacent members.

3. Carefully flush the rivet head ensuring no gouging to the adjacent member.4. Remove slag using a chipping hammer or chisel.5 Using an appropriate sized punch attempt to knock out the rivet.6 If rivet is keyed in and fails to move flush opposite head (tail) in accordance with

steps (1) and (2).7 Heat rivet from one side, using a cutting tip pierce through rivet. if applicable drill

a small hole through rivet prior to piercing.8 Remove slag then punch out rivet.9 If rivet remains keyed in, enlarge pierced hole leaving approximately 3mm of rivet

shank. This will ensure scarring of the adjacent member is avoided.10 Punch out remainder of rivet.

For plate thickness combinations of 40mm and greater

It will be necessary to simultaneously heat the rivet from both sides prior to piercing. Fromone side in the first instance, or both sides if later necessary.

Note: If scarring occurs then reaming in accordance with Clause 5.2.2 of this Manual willbe necessary before fitting bolts.

Option B

All of the foregoing where applicable except drilling to be used in lieu of piercing.