CONCRETE STRUCTURES IN ACID SULFATE SOILS

CONCRETE STRUCTURES IN ACID SULFATE SOILS

Hani Selim, Greg Forster and Gordon Chirgwin Bridge Branch, Roads and Traffic Authority, NSW

ABSTRACT

Acid sulfate soils (ASS) and potential acid sulfate soils (PASS) are natural soils which contain pyritic materials at various stages of oxidation . The oxidation of pyrites is a result of exposure to air. When water passes through such soils, sulfuric acid is leached out.

Engineering operations on potential and acid sulfate soils, such as mining, excavation, dredging and draining accelerate the exposure of pyritic material to air. These operations can speed up the production of acidic waters to many times the natural rate and hence result in deterioration of engineering structures located within or near the PASS or ASS.

This paper reviews deterioration mechanisms of concrete structures in acid sulfate soils, critically reviews methods for determination of exposure classification available for designers and specifiers, and suggests a new approach.

Hani Selim

Hani Selim is a structural engineer with BSc and MSc in civil and structural Engineering. He has over 10 years of experience in many aspects of concrete including: concrete technology, design and construction of precast concrete structures. Hani is currently engaged by the Roads and Traffic Authority, NSW providing specialised services on concrete-related issues.

Greg Forster

Greg Forster has been the Manager, Bridge and Structural Specifications within the Roads and Traffic Authority's Bridge Branch since 1994, and has been employed as a professional engineer within the Authority since 1979. Greg was the co-author of a paper entitled "Design of Short to Medium Span Bridges for Western NSW" presented to the 1994 AUSTROADS Bridges Conference.

Gordon Chirgwin

Gordon Chirgwin is currently the Manager, Bridge Policies and Standards with the Roads and Traffic Authority, NSW. He has 24 years experience in road and bridge engineering. His MSc thesis was on the early strength testing of concrete. He has co-authored a number of papers on the use of sorptivity in concrete specifications.

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INTRODUCTION

1. Potential acid sulfate soils (PASS) are natural soils which contain iron pyrite (iron sulfide, FeS2) or pyritic material in unoxidised state. The pH in the soils is generally between 6 to 7.

2. Similarly, acid sulfate soils (ASS), are naturally occurring soils containing pyrite, or pyritic material , which have begun to oxidise through exposure to oxygen. When water passes through the these soils, sulfuric acid is leached out. The pH of in the soils can he as low as 3.5.

3. The resulting sulfuric acid reacts with the minerals in the soil changing the soil properties. If the soil has insufficient buffering capacity to neutralise the acid, the soil-water, ground water and drainage water will all become acidic and will contain dissolved aluminium, iron and heavy metals.

4. Engineering operations on PASS and ASS, such as excavation, dredging and draining accelerate the exposure of pyritic material to air and hence speed up the production of acidic waters. Engineering structures in such aggressive environments are at great risk of deterioration. Coal mining and other rock excavation can result in similar exposure of sulfide rich materials to air and subsequent leaching.

5. Reported findings of locations containing acid sulfate soils in NSW include the floodplains of many rivers including Clarence River, Clyde River, Hawkesbury River, Hunter River, Macleay River, Manning River, Myall River, Nambucca River, Richmond River, Shoathaven River and Tweed River 1'2'34.

6. This paper reviews deterioration mechanisms of concrete structures in acid sulfate soils, critically reviews methods for determination of exposure classification available for designers and specifiers, and suggests a new approach.

DETERIORATION OF STRUCTURES IN ASS

GENERAL

7. Depending on the predominant chemical reaction, deterioration processes can be generally classified into three groups:

• leaching, which removes part or all of the hardened cement paste from concrete 5;

• deterioration by exchange reactions and by the removal of readily soluble compounds from the hardened cement paste 5;

• swelling deterioration, largely due to the formation of new, stable compounds in the hardened cement paste 6.

DETERIORATION DUE TO ACIDITY

8. Acidic waters tend to dissolve the carbonate layer on the surface of concrete, preventing further carbonation and thereby promoting the leaching of lime from interior regions of the concrete. Concrete will deteriorate because the free calcium hydroxide

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contained within the concrete matrix and the acids attacking it form water soluble salts which are subsequently leached.

9. The rate of acid corrosion of any concrete is controlled by the nature of the acid, the concentration of free hydrogen ions (the pH), and by the solubility of the calcium salts formed by exchange reactions with the salts dissolved in the water. These calcium salts, if soluble, are leached from the concrete 5.

DETERIORATION DUE TO SULFATES

10. The sulfates most detrimental to Ordinary Portland Cement are those of ammonium, calcium, magnesium, and sodium. Potassium, copper and aluminium sulfates are less harmful. Barium sulfate and lead sulfate which are insoluble in water do not affect concretes.

11. Damage to concrete is caused by expansive chemical reactions. The first reaction is between sulfate and the free calcium hydroxide liberated during the hydration of the cement, to form calcium sulfate (gypsum). The second reaction is between gypsum and the hydrated tricalcium aluminate C3A to form calcium sulfoaluminate (ettringite). The larger volume of the resulting products leads to concrete expansion, cracking, and disintegration6. The aggressiveness of soil containing sulfates is specified in terms of SO3 content and recently in terms of SO4 content.

12. Where the soils contain enough sulfides, the sulfate content of ground water collecting in construction pits, wells or boreholes may increase over a period of weeks to several times the original value. After the backfilling of the construction pits, the sulfate content soon drops to the previous level, since the supply of air has been interrupted. This explains why water samples taken from the construction pit are usually higher in sulfates than those obtained from exploratory drilling. Protective measures based on the higher sulfate content of water samples obtained from the construction pit would be excessively conservative and expensive since the formation of sulfates is in this case local and transient.

13. In moving water the aggressive acid sulfates may be replenished, whilst in stagnant water the acid sulfates become exhausted with time. In cohesive soils (clay) the seepage rate of ground-water is of the order 10-5 m/s while in granular soils, rates a hundred or even a thousand times higher are possible. In such soils, higher rates of deterioration should be anticipated.

14. In stagnant water, the dissolved salts will tend to combine with the components of the hardened cement paste. For example, the sodium sulfate content of ground-water will react with the calcium hydroxide in cement to form gypsum. The pores of concrete are sealed to a certain extent by the precipitated gypsum. As a result, a natural protective layer is developed on and near the concrete surface.

METHODS OF EXPOSURE CLASSIFICATIONS

GENERAL

15. There are a number of codes, standards and other references which deal with exposure classifications. This section reviews the available classification methods and

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aims to give guidance when selecting exposure classifications for ASS of various aggressiveness. According to the exposure classifications, concrete quality, chemical content restrictions, cover, and other requirements are determined.

16. In determining the classification of structural members in ASS, the designers/specifiers in conjunction with the Project Managers nned to weigh the possible changes in the environment, and hence classification, over the design life of the structure.

17. Since changes to the pH with time is dependant on many factors, there is no direct valid laboratory method capable of measuring potential pH. However, by careful study of various factors and examination of results from suitable tests I, experts would be able to predict potential changes to the pH within a reasonable range. It is recommended that such estimates should be obtained from the geotechnical consultant.

18. For example, if pH of ground water is measured at 7 at the investigation stage, but other tests have shown that the soil is potential acid sulfate soil, this means that pH can significantly drop as the soil becomes disturbed or drained. Therefore construction methods, future development, and other factors which result in draining or disturbing potential acid sulfate soil should be considered when determining the exposure classification.

19. The permeability of soil is another factor to be taken into account when determining the exposure classification. In this paper, soils with permeability less than le m/s are referred to as low permeability soils (eg clay) and soils with higher permeability are referred to as high permeability soils (eg sand). Free water streams included in the category of high permeability soils.

20. It is important that designers and specifiers ensure that appropriate and complete information is reported by the responsible investigation parties, evaluated and then used when selecting an exposure classification. Assessments of the potential sulfate content and acidity of leachates from mining activities and excavations should also be made where these may contribute to acid sulfate exposures of structural elements.

'92 AUSTROADS BRIDGE DESIGN CODE

21. The '92 AUSTROADS Bridge Design Code is based on a nominal structure life of 100 years '. The Concrete Section of the Code 8 gives Exposure Classifications are given in the order of increasing aggressiveness from A, Bl, B2 to C. "U" classification is used for other exposures subject to special consideration.

22. For ASS, the exposure classification "U" is applied since the specific environment for such soils is not included in any of the classifications A to C. The Code requires the designers/specifiers to identify such exposures and specify requirements to ensure durability. Thus in this Code, it is the designer's responsibility to draw limits and requirements for this particular exposure. The Code broadly considers that permeable soils with a pH < 4.0 or ground containing more than one gram per litre ( 1000 mg/I or 1000 ppm) of sulfate ions as aggressive. The Commentary to Section 5 9, gives little advice on the action to be taken.

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AS 3600 CONCRETE STRUCTURES

23. AS3600 j° is based on a nominal structure life of 40 to 60 years. The approach and classifications used this Standard are similar to that of '92 AUSTROADS. The commentary for the Standard 11 lists some references for guidance to limits and requirements to be specified for exposure classification "U".

AS 3735 CONCRETE STRUCTURES FOR RETAINING LIQUIDS

24. AS 3735 12 is based on a nominal structure life of 40 to 60 years. Four basic exposure classifications in order of increasing aggressiveness from A to D are given in this Standard. The classification is in line with '92 AUSTROADS and AS 3600 but with an additional classification D in the absence of classification U. Comprehensive guidance is given in the Supplement 13 to the Code. It should be noted that for all concrete surfaces in exposure classification D, the Standard requires such surfaces be isolated from the attacking environment.

TABLE 1

EXTRACT FROM AS 3735 EXPOSURE CLASSIFICATION - SULFATE-CONTAINING SOILS

SO4 Content Ground water replenishment rate (ie soil permeability)

In Soil %

In water mg/1 or ppm

Low (eg clay) High (eg sand)

<0.2 400 A2 B1

0.2 - 0.6 400 - 1500 B1 B2 (or B1 with SR cement)

0.6 - 1.2 1500 - 30000 B1 B2, with SR cement

1.2 - 2.4 3000 - 6000 B2 (or B1 with SR cement)

C, with SR cement

> 2.4 > 6000 B2, with SR cement

D

Notes :

1. SR cement:

Sulfate-Resistant cement

2. PPm:

part per million

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TABLE 2

EXTRACT FROM AS 3735 EXPOSURE CLASSIFICATION -ACIDIC SOILS

Acidity measure

Ground water replenishment rate (ie soil permeability)

pH Low (eg clay) High (eg sand)

> 6.5 Al B1

5.5 - 6.5 A2 B2

4.5 - 5.5 A2 B2, with calcareous aggregate and increased cover to 125%

of nominal

3.5 - 4.5 B1 C, with calcareous aggregate and increased cover to 125%

of nominal

< 3.5 Bl, with calcareous aggregate and increased cover to 125 %

D

Notes

Calcareous aggregate is a limestone aggregate

The exposure classifications are determined for a range of environments which are:

1. Fresh water

2. Sewage and waste water

3. Sea water

4. Corrosive liquids, vapours and gases

5. Other liquids

6. Ground water

25. The applicable item for ASS is No. 6, in which a broad range of classifications is given and reference made to the Supplement for assistance. The applicable item, together with material from the Supplement, is rearranged in Tables 1 and 2.

26. The exposure classification for the surface of a member is to be determined from this Standard and from AS 3600 for the most severe environment, or use, to which the concrete will be subjected during its operational life. However in the case of ASS, AS 3735 requirements are more detailed than AS 3600 and are preferred.

27. For ASS, the above information suggests that the exposure classification needs to be determined for both sulfate aggressiveness and for acidity and the higher

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classification from the two is to be used in accordance with the qualifications given in the Standard (eg the use of Sulfate Resistant cement and/or the use of limestone aggregates).

28. The Standard recognises the following as methods for obtaining such concrete:

• the use of sulfate resistant cements (superseded cement classification Type D)

• the use of pozzolanic material (eg fly ash) blended with Ordinary Portland Cement ie blended cements

• the use of a waterproofing agent with Ordinary Portland Cement.

29. Sulfate resistant concrete and RTA preferred methods for obtaining sulfate resistance are discussed in detail in later sections.

AS 2159 PILING - DESIGN AND INSTALLATION

30. AS 2159 14 is based on a nominal structure life of 40 to 60 years.

31. This Standard and Supplement 15 use different exposure classifications to '92 AUSTROADS and the other Australian Standards reviewed above. The classification is self explanatory and comprises Non-aggressive, Mild, Moderate, Severe and Very Severe.

32. The relevant classification for ASS is rearranged and summarised in Tables 3 and 4. The Standard uses sulfate expressed as SO3 . To maintain consistency of this paper and to enable comparisons, the SO3 is converted in the appendix to SO4 (using SO3 = 0.83 SO4).

TABLE 3

EXTRACT FROM AS 2159 - EXPOSURE CLASSIFICATION FOR CONCRETE PILES - SULFATE-CONTAINING SOILS

SO4 Exposure Classification

In Soil %

In water (mg/1 or ppm)

Low Permeability Soil (eg clay)

High Permeability Soil

(eg sand)

<0.25 375 Non-aggressive Non-aggressive

0.25 - 0.62 375 - 1250 Non-aggressive Mild

0.62 - 1.25 1250 - 3125 Mild Moderate

1.25 - 2.5 3125 - 6250 Moderate Severe

> 2.5 > 6250 Severe Very Severe

Note : ppm: part per million

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TABLE 4

EXTRACT FROM AS 2159 - EXPOSURE CLASSIFICATION FOR CONCRETE PILES - ACIDIC SOILS

Acidity measure

Exposure Classification

pH Low Permeability Soil (eg clay)

High Permeability Soil (eg sand)

> 6.5 Non aggressive Non-aggressive

5 - 6 Non-aggressive Mild

4.5 - 5 Mild Moderate

4 - 4.5 Moderate Severe

<4 Severe Very severe

33. The sulfate limits of this Standard approximate those of AS 3735. However direct matching for the two different classifications of the two standards is not appropriate since specified minimum concrete strengths and cover differ. AS 2159 refers to AS 3735 for design of concrete which is exposed to severe and very severe sulfate environments. AS 2159 also uses separate tables for acid and sulfate exposure. This limits the usefulness of the standard in ASS conditions.

OTHER CLASSIFICATIONS

34. In a report recently published by the Building Research Establishment 16, exposure classifications are given differently to the above reviewed standards and codes. No nominal structure life is provided in the BRE recommendations. The significance of the classification is the progressive selection of exposure classification and the relationship between various exposures. The SO4 and pH of soils and natural ground water are measured and classified accordingly.

35. Where pH is greater than 5.5, classification is dependant only on the SO4 concentration. There are five basic classes for SO4 and two sets of modifications to these classes to be considered progressively according to types of exposure and types of structure. Various cement types are also specified within the basic classification. Where pH is less than 5.5, sites are classified first on basis of SO4 concentration as above and then reclassified on basis of pH.

36. The BRE method of determining the SO4 content uses a two stage process. The initial stage uses a simple method to detect the presence of SO4. If this method gives a result above a threshold, then a more accurate test is applied to determine the SO4 content for design purposes. Since the scope of the BRE report covers other structures as well as bridges and road structures, only classifications and modifications applicable

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to bridge and road structures in ASS are referred to in this report. These classifications and modifications are rearranged in Tables 5 and 6, respectively.

TABLE 5

EXTRACT FROM BRE REPORT 16 - EXPOSURE CLASSIFICATION - SULFATE-CONTAINING SOILS

SO4 content in ground water (mg/I or ppm)

Cast -in-situ concrete 140 mm to 450 mm in thickness

Cast-in-situ concrete over 450 mm thickness,

and

Precast concrete members which have had additional air curing after normal curing cycle. (Several weeks air curing)

Low Permeability

Soil (eg clay)

High Permeability

Soil (eg sand)

Low Permeability

Soil (eg clay)

High Permeability

Soil (eg sand)

< 400 1 1 1 1

400 - 1400 1 2 1 1

1400 - 3000 2 3 1 2

3000 - 6000 3 4 2 3

> 6000 4 5 3 4

Note ppm : part per million

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TABLE 6

EXTRACT FROM BRE REPORT 16 - MODIFICATION TO EXPOSURE CLASSIFICATION FOR ACIDITY

Exposure of Foundation

members

pH Changes in exposure Class (+ / - = increase / decrease the class determined from the previous table)

Low Permeability Soil

(eg clay)

High Permeability Soil

(eg sand)

Natural

ground water

> 5.5 No change No change

3.5 - 5.5 No change +1

< 3.5 +1 +1

Wastes or

made-up

ground

> 5.5 No change +1

4.5 - 5.5 +1 +2

< 4.5 +1 +3

37. Table 5 determines the exposure classification in accordance with SO4 content and modifies the classification according to the member size and the mobility of the ground water. Table 6 shows the changes to be made to the classification determined from Table 5 according to the pH and the nature of the ground water. This last modified classification is used to determine the requirements for cement type, minimum cement content, maximum free water - cement ratio and concrete protection.

RECOMMENDED EXPOSURE CLASSIFICATIONS

38. Except for the BRE method, all methods above classify exposure of concrete structures by two separate sets of rules for acidity and sulfate. Another common feature of all methods above (excluding the bridge design code and BRE method) is the nominal structure life of 40 to 60 years. These features and the broad requirement of the bridge design code highlighted the need for a new classification method specifically designed for structures in acid sulfate soils. The new method is sought to incorporate well defined, clear and appropriate requirements reflecting the nominal structure life of 100 years.

39. Based on available information, Tables 7 and 8 are developed to relate exposures applicable to bridge foundations in ASS to the classifications of '92 AUSTROADS. Exposures are given in term of B1, B2, C, and U. The exposure classification type A is not used as B1 is the minimum requirement for members in soil or water under '92 AUSTROADS requirements.

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TABLE 7

RECOMMENDED EXPOSURE CLASSIFICATION IN TERMS OF '92 AUSTROADS FOR LOW PERMEABILITY SOIL

SO4 (mg/I or

PPm)

Equivalent Exposure Classifications in terms of '92 AUSTROADS

pH

3.5 > 3.5

< 4.5

> 4.5

< 5.5

> 5.5

< 400 U U B1 81

400 - 1500 U U B1 B1

1500 - 3000 U U BI B1

3000 - 6000 U U U U

> 6000 U U U U

TABLE 8

RECOMMENDED EXPOSURE CLASSIFICATION IN TERMS OF '92 AUSTROADS FOR HIGH PERMEABILITY SOIL

SO4 mg,/1 or

(ppm)

Equivalent Exposure Classifications in terms of '92 AUSTROADS

1 pH

3.5 > 3.5 4.5

> 4.5 < 5.5

> 5.5

<400 U U B2 B1

400 - 1500 U U C B2

1500 - 3000 ti U U U

3000 - 6000 U U U U

> 6000 U U U U

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RECOMMENDED DESIGN REQUIREMENTS

40. In this section, general design recommendations for the exposure classifications developed in the pervious section are given. These design recommendations are discussed in more details in the RTA Technology Review Report 1996 17 which draws

27 to upon a number of other works 5,6,18 The requirements are expressed in terms which relate to RTA Specification B80 "Concrete Work for Bridges" 28.

41. Except for exposure classification 'Ir in Tables 1 a and 1 b, concrete quality, cover and other durability requirements are determined according to the exposure classification in the normal fashion of '92 AUSTROADS. For exposure classification U, recommended design treatments are given in Tables 2a and 2b. The two tables relate exposures applicable to bridge foundations in ASS to the classifications of '92 AUSTROADS with additional measures and qualifications.

42. Design requirements B1, B2, C in Tables 9 and 10 indicate equivalent concrete requirements to that specified for the relevant exposure classification of '92 AUSTROADS in addition to the following :.

• Design requirement Cl indicates design requirement C with the addition of full isolation of the concrete surface from the aggressive environment.

• Environments under the dark horizontal line require sulfate-resisting blended cement.

• Environments to the left of the dark vertical line require blended cement concretes containing calcareous aggregate with an increased concrete cover unless design requirement C1 is achieved. Alternative design solutions resulting in neutralisation of the acids may also be adopted.

43. For retaining and culvert structures, high permeability soil condition and its relevant design requirements should be always used. This is due to the nature of construction of these structures requiring draining and granular fill. The following modifications to Table 10 for such structures are recommended :

• Calcareous aggregate should not be used

• B2 becomes B2 plus full isolation

• C becomes Cl

• C 1 : no change

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TABLE 9

RECOMMENDED DESIGN REQUIREMENTS FOR EXPOSURE CLASSIFICATION TYPE U OF TABLE 7 FOR LOW PERMEABILITY SOIL

SO4

(mg/I or

ppm)

Recommended Design Requirements

pH

< 3.5 4.5 > 3.5

> 4.5 ..._ 5.5

> 5.5

<400 B2 B1

400 - 1500 B2 B1

1500 - 3000 B2 B1

3000 - 6000 C B2 B2 B2

> 6000 Cl C B2 B2

TABLE 10

RECOMMENDED DESIGN REQUIREMENTS FOR EXPOSURE CLASSIFICATION TYPE U OF TABLE 8 FOR HIGH PERMEABILITY SOIL

SO4

(mg/1 or

ppm)

Recommended Design Requirements

pH

5 3.5 > 3.5 4.5

> 4.5 5.5

> 5.5

< 400 Cl C

400 - 1500 Cl C

1500 - 3000 Cl C C B2

3000 - 6000 Cl Cl C C

> 6000 Cl Cl Cl Cl

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GENERIC PROCEDURE FOR ADDRESSING DEVELOPMENT OF NEW STRUCTURES IN ASS

44. The flowchart in Appendix A summarises the proposed procedures to be followed by designers, specifiers and/or Project Managers in the design, specification and construction of structures in ASS. The procedures are grouped in three main stages:-

• the investigation stage,

• the design and review stage, and

• construction stage.

45. At each of these stages a number of steps is recommended. It is essential that designers, specifiers and project managers communicate at all stages of the project so as to deliver adequate, buildable and economical structures. Monitoring and evaluation of design, specification and construction methods for structures in ASS in a project will not only ensure that project requirements are met but also benefit other projects.

46. Owing to the relative infancy of this area of design, expert advice should be sought when assessing the soil conditions and reviewing the proposed design approach. The design recommendations contained in this report should be considered in the context of the '92 AUSTROADS Bridge Design Code and RTA Specification B80 -Concrete for Bridgeworks.

CONCLUSION

47. Concrete structures in ASS are at great risk of deterioration due to the acidity of, and sulfate ions in, such soils. Exposure classification of concrete structures in ASS depends on many factors such as the availability of air at during construction or over the life time of the structure, soil permeability, the level of acidity and sulfate ion concentrations. Existing classification methods and design recommendations are critically reviewed. A new classification method which takes into account all relevant factors is proposed, together with design recommendations compatible with the '92 AUSTROADS Bridge Design Code.

DISCLAIMER

48. The opinions expressed in this paper are entirely those of the Authors, and do not necessarily represent the Policy of the Roads and Traffic Authority of NSW.

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REFERENCES

1. RTA Guidelines " Acid Sulfate Soil", 1996.

2. Environmental Impact Statement for State Highway 10-Pacific Highway, Chinderah Bypass. Report by GHD for RTA, 1991.

3. RTA Policy and Procedures "Acid Sulfate Soil", RTA, 1995.

4. White I. And Melville M.D., "Treatment and Containment of Potential Acid Sulfate Soils", CSIRO Technical Report No. 53, 1993.

5. Biczok I., "Concrete Corrosion - Corrosion Protection", Publishing House of the Hungarian Academy of Sciences, Budapest, 1972.

6. Guirguis S. , "Durable Concrete Structures", CIA Technical Note TN57, March 1986.

7. '92 AUSTROADS "Bridge Design Code", Section One - General - Code, AUSTROADS 1992.

8. '92 AUSTROADS "Bridge Design Code", Section Five-Concrete - Code, AUSTROADS 1992.

9. '92 AUSTROADS "Bridge Design Code", Section Five-Concrete -Commentary, AUSTROADS 1992.

10. AS 3600 "Concrete Structures", Standards Australia, 1994.

11. AS 3600 Suppl "Concrete Structures-Commentary", Standards Australia, 1990.

12. AS 3735 "Concrete Structures for Retaining Liquids", Standards Australia, 1991.

13. AS 3735 Suppl " Concrete Structures for Retaining Liquids - Commentary", Standards Australia, 1991

14. AS 2159 " Piling-Design and Installation", Standards Australia, 1995.

15. AS 2159 Supp 1 "Piling-Design and Installation-Guidelines", Standards Australia, 1996.

16. Building Research Establishment Digest 363, "Sulfate and Acid Resistance of Concrete in the Ground", January 1996.

17. RTA Technology, "ASS, Concrete Structures - Advice for Design and Construction", Review Report , May 1996.

18. ACI Committee 515, "Guide for the Protection of Concrete against Chemical Attack by Means of Coatings and Other Corrosion Resistant Materials", ACI Manual Part 5.

19. Al-Amoudi 0.S., Maslehuddin M. and Saadi M.M., " Effect of Magnesium Sulfate and Sodium Sulfate on the Durability Performance of Plain and Blended Cements". ACI Materials Journal, V.92, No.1, Jan-Feb 1995.

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20. Bartholomew R.F., "The protection of concrete piles in aggressive ground conditions : an international appreciation", symposium paper : Recent Developments in the Design and Construction of Piles. Institution of Civil Engineers, 1979.

21. Beal D.L. and Brantz H.L., " Assessment of the durability characteristics of triple blended cementitious materials", Paper presented at Fly Ash, Silica Fume, Slag and Natural Pozzolans in Concrete, Fourth International Conference, Istanbul, Turkey, May 1992.

22. Fattuhi N.I. and Hughes B.P., "Effect of acid attack on concrete with different admixtures or protective coatings", Cement and Concrete Research, vol 13, 1983 pp 655-665.

23. Fidjestol P. and Frearson J. " High-Performance Concrete Using Blended and Triple Blended Binders" .High Performance Concrete Proceedings, ACI International Conference, Singapore, 1994. ACI , SP 149-8.

24. Harrison W.H., "Durability of Concrete in Acidic Soils and Waters", Concrete , February 1987.

25. Hughes B.P. and Guest J.E., "Limestone and Siliceous Aggregate Concretes Subjected to Sulphuric Acid Attack", Magazine of Concrete Research, Vol 30, No 102, March 1978 pp 11-18.

26. Mangat P.S. and Khatib J.M., "Influence of Fly Ash, Silica Fume, and Slag on Sulfate Resistance of Concrete", ACI Materials Journal, Vol. 92 No. 5, Sept-Oct. 1995.

27. Redner J. A., Randolph P. H. and Esfandi E., " Evaluation of Protective Coatings for Concrete", Paper from the Proceedings of SSPC 91 Protective Coatings for Flooring and Other Concrete Surfaces, 1991.

28. RTA B80 Concrete Work for Bridges.

Note : '92 AUSTROADS "Bridge Design Code", Sections 1 to 5 have been recently incorporated in "Australian Bridge Design Code - Limit States Format" Standards Australia HB77-1996.

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APPENDIX A

Flowchart for Dealing with ASS in Design and Construction

Investigation

Obtain briefing on the nature of ASS and PASS.

i Gather monitored data from completed projects dealing with ASS / PASS

Obtain existing soil conditions for permeability, pH, and SO4

r Obtain expert advice on potential pH and • SO4 over life time of structure

Design and Review

Determine exposure classifications and durability design requirements

Input into the overall structural design, as required

Input into the concrete section design and technical specification, as required

Specify special concrete mix requirements

' Obtain expert advice on type of coatings and specify as required

Specify other protection method, as required

• Construction

Monitor compliance with design and

• specification

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