Handbook for the Identification of Alkali-Silica Re Activity in Highway Structures,Revised Edition

SHRP C-315, Revised Edition

Handbook for the Identification ofAlkali-Silica Reactivity in Highway Structures,

Revised EditionThe following provides the full text with pictures of SHRPC-315, one of the key products of the Strategic HighwayResearch Program, Contract C-202, ASR project developedby the National Research Council, 2101 ConstitutionAvenue N.W., Washington, DC 20418. Author of theoriginal manuscript is David Stark, ConstructionTechnologies Laboratories, Inc., Skokie, IL, USA.

A Table of Contents has been provided for yourconvenience. You can directly access the chapter of interestby clicking on the subject below.

The original text is supplemented to reflect recent findingsand conclusions developed by the AASHTO ASR LeadState Team Members since this document was printed in1994. For reference, all text that has been added or modified from the originaldocument appears in Italics. A new method for field Identification of ASR has alsobeen added based on research conducted at the Department of Defense Los AlamosNational Laboratories.

Table of Contents

Foreword

Introduction

Organization of Handbook

1. The Nature of Alkali-Silica Reactivity (ASR)

2. ASR in Pavements

3. ASR in Bridge Structures

Alkali Silica Reactivity: Library: Handbook for Identification of ASR

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4. Identification of ASR gel in Field Structures

a. Introduction

b. Uranyl Acetate Procedure - (Now AASHTO T 299)

c. Interpretation

Foreward

Alkali-Silica Reactivity (ASR) is a major cause of the deterioration of highwaystructures and pavements in the United States. The Strategic Highway ResearchProgram (SHRP) has addressed this problem through its Project C-202, Eliminatingor Minimizing Alkali-Silica Reactivity. One task of this research was to find meansto mitigate damage caused by ASR in existing concrete structures and pavements.The first steps toward achieving this goal are to detect ASR and to distinguish it fromother types of damage, particulalry in its early stages. This handbook is intended toserve this purpose. It uses color photographs of actual examples to illustrate the ASRdamage in a number of field structures. It then describes a simple and rapid chemicaltest for ASR detection. An early diagnosis of the problem should greatly help in thetimely and economical repair or rehabilitation of the affected concrete structure.

Inam JawedProject ManagerStrategic Highway Research Program

Addendum from the AASHTO ASR Lead State Team

Since the publication of this C-315 Handbook, Department of Energy researchers,Bill Carey and George Guthrie, at the Los Alamos National Laboratories, havedeveloped a new staining technique for detecting ASR in field structures. Thismethod, called ASRDetect, is simple, practical, environmentally benign, andinexpensive. Since we expect it to be commercially available around the first part of1999, and since it shows sufficient promise as a viable ASR screening method, wehave added it as an addendum to this Handbook.

Introduction

This handbook provides guidance for the field identification of Alkali-SilicaReactivity (ASR) in portland cement concrete structures such as highway pavementsand bridges. ASR development is assessed on two bases : 1) the occurrence anddisposition of cracking and displacement of concrete, and 2) the presence of reactionproducts from ASR. Descriptions and color photographs provide detailedinformation.

Other causes of cracking or volume changes, such as freezing and thawing, corrosionof reinforced steel, superimposed loading, or plastic shrinkage, may have occurred inthe structure under inspection. Distress similar to that resulting from ASR but not



caused by ASR is also identified. The reader should keep in mind that distress toconcrete can be very complicated, and that it is not uncommon for secondary distressmechanisms such as freezing and thawing and corrosion of reinforced steel to beaccelerated once the integrity of concrete is affected by ASR-induced cracking. Thishandbook, therefore, is meant to act as a guide for an initial assessment of potentialASR distress in the field, not for definitive assessment of distress mechanisms. Anyfield observations should be confirmed in the laboratory by an experiencedpetrographer before making definitive conclusions.

The descriptions and photographs of evidence of ASR presented in this handbook arebased on almost 30 years of field and laboratory investigations of a wide variety ofconcrete structures. Most of the information presented was obtained under SHRPProject C-202, "Eliminating or Minimizing Alkali-Silica Reactivity." The uranylacetate procedure for identifying ASR gel reaction products was developed by Drs.K. Hover and K. Natesaiyer of Cornell University. (1, 2)The ASRDetect procedurewas developed by Bill Carey and George Guthrie at the DOE Los Alamos NationalLaboratories.

References

1. NATESAIYER, K. and Hover, K.C., "Insitu Identification of ASR products in Concrete",Cement and Concrete Research, Vol. 18, May 1988, pp. 455-463.2. NATESAIYER, K. and Hover, K.C., "Some Field Strategies of the New Insitu Method forIdentification of Alkali Silica Reaction Products in Concrete", Cement and Concrete Research, Vol.19, September 1989, pp. 770-778.

Organization of Handbook

This handbook is divided into five sections. Color photographs are used thoughout thehandbook to aid in accurate identification. Section1 describes the nature of ASR andits causes and effects. Section 2 deals with the manifestations of ASR-related volumechanges in highway pavement. Section 3 covers ASR in bridge structures. Section 4describes a rapid field procedure to identify the presence of ASR reaction products inconcrete. Section 5 describes a new, easier method to accomplish the same recentlydeveloped by the DOE Los Alamos National Laboratories. The presence of thereaction products is indisputable evidence of ASR, but it does not necessarily reflectdevelopment or severity of distress. Thus, assessment of associated distress togetherwith identification of reaction products provides the greatest assurance whetherexpansive ASR has developed in the concrete structure. Confirmation of ASR bypetrographic analysis is recommended to reach reliable conclusions that the distressis indeed due to ASR expansion.

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SHRP C-315, Revised Edition - Continued

1. The Nature of ASR

Return to Table of Contents

Three requirements must be met for expansive ASR to occur : 1) reactive forms ofsilica or silicate in the aggregate, 2) sufficient alkali (sodium and potassium )primarily from the cement, 3) and sufficiently available moisture in the concrete. Ifany one of the three requirements is not met, expansion due to ASR cannot occur.

In its simplest form, ASR can be visualized as a two-step process :

Alkali + Silica Gel Reaction Products1.

Gel Reaction Products + Moisture Expansion2.

Actual expansion occurs in the second step when the ASR gel reaction product swellsas it absorbs moisture. Potentially expansive gel reaction product does not formunless the first step occurs.

As a general rule, two of the three requirements for ASR, cement alkali and reactivesilica, are basically fixed components of the concrete and therefore present thepotential for expansion, regardless of exposure condition. However, alkali levels canbe increased from those in initial mix by external sources such as from salt water andmist in coastal areas or from deicer salts, or the alkalis present can be concentratedin areas of the concrete causing localized reaction. Some of the causes ofconcentration can be wetting and drying cycles in the concrete or cases wherereinforced concrete is being protected by cathodic protection. The third requirement,moisture availability, is a major variable in concrete and has a significant impact onthe severity of distress and volume change due to ASR.

Moisture availability in concrete varies significantly with distance from exposedsurfaces in most, if not all, highway structures. This is most pronounced under severeatmospheric drying coditions such as those in arid desert-like regions in thesothwestern United States. The resulting crack pattern associated with ASR maythereby become accentuated through shrinkage induced by prolonged, severe drying.It is thus not uncommon for secondary distress mechanisms such as drying shrinkage,freezing and thawing and corrosion of reinforced steel to be accelerated once theintegrity of concrete is affected by ASR-induced cracking.

Restraint, due both to abutting concrete and to embedded reinforcing steel, influencesthe development of cracking associated with ASR. Its effects are observed in


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highway pavements and bridge structures, as will be seen in the illustrations.Cracking associated with ASR is not uniformly developed throughout concretemembers due in part to restraint. Creep is a major factor that tends to relieveASR-induced stress. Since neither restraint nor creep are uniform in all directions,ASR-related distress is not uniformly developed. For example, abutting pavementslabs offer restraint parallel to the longitudinal direction of the pavement. Crackingtherefore tends to be more pronounced in the longitudinal direction; that is,differential movement is greater in the transverse and vertical directions, resulting inthe typical cracking illustrated in the photographs in this handbook. Finally,nonuniform cracking patterns can be caused by differences in wetting and drying inportions of a concrete member as by sprinkling or watering systems, or leakage fromjoints in the deck on bridge substructures.




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2. ASR in Pavements


FIG.1 - Close-up ofpavement surfaceshowing very earlydevelopment of crackingassociated with ASR.Cracks show generallyrandom orientation withno preferred direction ofstrongest crackdevelopment. Suchcracking is more visibleon smooth surfaces thanon textured or groovedsurfaces, and can beenhanced visually by viewing after partial drying of a surface wetted withwater ( e.g. after a rain ) or with a 1 % Potassium Iodide (KI) solution.Appearance at these early stages can easily be misinterpreted as dryingshrinkage cracking.

FIG.2 - Pavement surfaceshowing slightly greaterdevelopment of crackingthan is illustrated in Fig.1. Cracks show generallyrandom orientation withno strongly preferreddirection. Longitudinalgrooving tends to obscurecracks. Gel appearing asa translucent wet depositor as a white deposit maybe visible at this stage.Width of cracks varies,with the widest cracks usually visible in portions of the slab where there isless restraint, e.g. the edges of the pavement.


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FIG.3 - A well-definedcrack pattern associatedwith the development ofASR in highwaypavement. Crack patternis commonly identified as"map-cracking" or"pattern-cracking."Orientation ofpredominant cracks islongitudinal as shown.Crack pattern is generallydeveloped uniformlyacross the width of thepavement, although cracks in wheel paths may be more apparent due toinfiltration of dirt and apparent greater width due to crumbling of crackedges. Both result from traffic wear. Often pavement that has reached thislevel of distress also exhibits a sheen or slightly wet look, particularly inthe wheel path, caused by spreading of the silica gel exuding from thecracks. Although the crack pattern is similar for jointed and continuouslyreinforced concrete pavement (CRCP) there is usually a higherconcentration of longitudinal cracking at the joints in jointed pavementthan is visible at this stage at the normal transverse cracks that develop inCRCP. In both cases these areas tend to be the weak points of thepavement where spalling will occur as the reaction progresses.

FIG.4 - Closer view ofwell-developed pattern ofcracking associated withASR, as viewedtransversely across jointedpavement. Patternsomewhat resembles thatwhich develops on driedmud flats, but tends toshow more prominentcracks in longitudinal (leftto right) direction ofpavement. Cracks may befilled with secondaryreaction products which may or may not be ASR gel.



FIG.5 - Close-up view ofsevere cracking associatedwith ASR in jointedpavement. Orientation ofpredominant cracks islongitudinal (left to right).Interconnecting cracks arerandomly oriented.Virtually all cracks areopen and are not filledwith secondary deposits atthe surface. Severe desertdrying occurs in thisregion, thus probablyincreasing the severity of cracking. At this stage of damage spalling atjoints is normally observed, as well as secondary damage by freeze-thawin areas subjected to freeze-thaw cycles.

FIG.6 - Cylindricalsurfaces of 4-inchdiameter cores removedfrom area of pavementshown in Fig. 5. Notepredominance of cracks inupper half of pavement,which is typical ofASR-related distress.These cracks are moresharply defined on thesepartially dried cores bywater remaining in thecracks, thus producingrelatively dark fringes that follow cracks. Note vertical cracks near topsurface, and sub horizontal orientation of many cracks below the surface.ASR has, however, developed through the full thickness of the pavementslab. Cracking is not evident in the bottom half due to restraint producedby the weight of the concrete in the top half.



FIG.7 - Severe crackingassociated with ASR incontinuously reinforcedconcrete pavement(CRCP). Cracks are mostfrequently oriented inlongitudinal direction ofpavement (top to bottomin photo), and areinterconnected by finertransverse or randomcracks, producing agenerally rectilinear crackpattern. Relatively smoothwearing surface shown in photo, in contrast to grooved and texturedsurfaces, enhances appearance of cracks.

FIG.8 - Four (4) - inchdiameter cores taken fromCRCP shown in Fig. 7.Note shallow depth (1 to 2½ in.) of vertical cracksthat appear aswell-defined longitudinaland transverse or randomcracks at the wearingsurface. Verticallongitudinal cracks alsoextend upward about 2 to3 inches from bottom ofmiddle core and core atright side. Although not readily seen in the photo, cracks near mid-depth inthe cores, in the vicinity of the reinforcing steel, are oriented generallyhorizontally, in contrast to the vertical orientation of cracks at the top andbottom surfaces. This is due to localized restraint provided by thereinforcing steel.



FIG.9 - An early stage of crackingassociated with ASR in jointedpavement. Occasionally, crackingfirst appears or is more severealong joints. This may lead toconfusion with D-cracking (seeFig. 10). Note that, in crackingassociated with ASR, numerousindividual cracks areapproximately normal to thedirection of the joint. It must benoted that, in areas that experiencea number of freeze-thaw cycles,secondary damage due tofreeze-thaw can occur at the jointsresulting in a secondary crackingpattern parallel to the joint whichcan easily be confused withD-cracking.

FIG.10 - D-cracking due tofreeze-thaw deterioration of coarseaggregate along transverse joint. Incontrast to cracking associatedwith ASR, cracks are roughlyparallel to the adjacent joint.Cracking along joint that has beeninduced by ASR, as in Fig.9, isusually normal to the joint and isassociated with a faintermap-cracking elsewhere in thepavement slab. D-crackingnormally progresses away onlyfrom joints, intermediate cracks,and free edges of pavement slabs.ASR affected pavement withsecondary freeze-thaw damageinitiated by the ASR cracking willnormally exhibit a combination of the two types of cracking patterns.



FIG.11 - Fracture surfaceof 4 inch diameter corefrom pavement whereASR has developed. Notewhite deposit in severaldark coarse aggregateparticles, with particularbuildup along peripheryof particles. This depositcontains ASR gel reactionproduct that ischaracteristic of reactedparticles (arrows).

FIG.12 - Smooth, lappedsurface of concreteshowing reaction rims oncoarse aggregate particles(paired arrows),microcracks throughparticles, and white ASRgel reaction products(single arrow). Confirmedgel deposits are positiveevidence that ASR hasoccurred. Reaction rimsare characterized asdarker rims surroundingthe aggregate. Note that cracking pattern extends from coarse aggregatethrough the paste, through another coarse aggregate particle, etc.creating a continuous crack pattern throughout the concrete matrix. TheASR gel reaction products appear to have migrated through this crackpattern demonstrating the relative fluidity of the gel.








3. ASR in Bridge Structures


FIG.13 - Cracking associated withASR at mid-span in bridge deck.Predominant cracks are orientedlongitudinally with respect to deck(top to bottom in photo), and areinterconnected by short, tightmicrocracks that extendtransversely or randomly betweenlongitudinal cracks. Cracking maybe more severe over girders. Noconsistent relationship existsbetween location of cracks andsteel in top reinforcing mat.

FIG.14 - Characteristic crackingassociated with ASR in corner ofbridge deck. Cracks tend to "curve"around corner from transverseorientation at end of deck tolongitudinal orientation towardmiddle of span (See Fig.13). End ofdeck is along tarred strip at bottomof photo. Cracking pattern is due torestraint developed by thereinforcing steel and other concretemembers in and around the deck.Areas, such as around drains,where rainwater and/or solubilizeddeicer flows or collects on a deck tend to show more severe cracking.


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FIG.15 - Four (4) inch diameter core takenfrom area of bridge deck shown in Fig.14.Major cracking occurs full-depth in the coreand is enhanced by wetting and partialdrying. Dark bands follow cracks that stillcontain water. Initiation of cracking isattributed to ASR. Restraint by reinforcingsteel to volume change may have influencedcrack pattern.

FIG.16 - Longitudinal crack, along top ofparapet wall, associated with ASR. Other,much finer cracks form network of crackingon top surface. Such cracking could beattributed to drying shrinkage or corrosionof embedded steel. Corroborating evidence,such as petrographic analysis, is necessaryto verify association of ASR with cracking.



FIG.17 - Cracking associated withASR in end block of concrete guardrail on bridge deck. This type ofcracking could result from freezingand thawing. In essentiallyfrost-free climates, ASR is thelikely cause of cracking. Individualcracks are stained and filled withcalcium carbonate and ASR gel.Evidence of overall abnormalexpansion due to ASR may not beapparent in such concrete units. Donot interpret this type of crackingas confirming evidence of ASR inareas of freezing and thawing. In these cases, however, initial cracking due to ASRmay lead to faster progression of freeze-thaw damage by creating a pathway formoisture to enter into the concrete mass expanding the cracks upon freezing.

FIG.18 - Cracking and differentialmovement of abutting sections ofparapet wall in bridge structureaffected by ASR. Joint is tightlyclosed and lateral offset hasoccurred. Cracking and spallinghave developed on left side of joint,and cracking and incipient spallinghave developed around embeddedmetal plate on right side. Depositsthat most likely include ASRreaction products are clearlyvisible in and around cracks. Insuch cases confirmation should bemade that distress has not resulted from other factors, such as foundationmovements, freezing and thawing or vehicle impact. In cases where cracking hasadvanced to this stage the visible damage, although initiated by ASR, is probablydue to a combination of factors and the structure will continue to deteriorate. Inaddition, damage immediately attributable to ASR can continue at an expedited ratebecause the advanced cracking provides easy channels for greater ingress ofmoisture and external sources of alkali such as from deicer salts. This effect isparticularly noticeable in cases where extent of reaction is limited by the amount ofmoisture or available alkali.



FIG.19 - Major vertical crack with lessprominent horizontal and random cracks inend of parapet wall. White deposit at base ismixture of ASR gel and calcium carbonate.This evidence is typical of advanced stagesof ASR. However, such deposits mostcommonly consist of calcium carbonate,which by itself is not indicative of ASR.Presence of occurrence of ASR expansionand of ASR gel must be confirmed in otherways.

FIG.20 - Closed joint between sections ofparapet wall may have resulted fromexpansion due to ASR, as shown. Inspectionshould be made to determine if a foundationshift may have caused a tight joint. Suchevidence should be used only as supportingevidence of ASR unless indicated otherwise.Evidence of closed joints such as the one inthe picture throughout the structure areusually indications that the cause is ASRrather than foundation shifts.



FIG.21 - Horizontal crackingextending the length of the pier capof bridge over fresh water. Suchcracking is often associated withASR but might also be due tocorrosion of embedded reinforcingsteel, or a combination of the two.This area is moist and collectscondensation thus insuringsufficient moisture for ASR. InitialASR cracking allows the ingress ofmoisture and carbon dioxide intothe concrete close to the steel,resulting in a drop in pH aroundthe steel providing the right conditions for initiation of corrosion. Corroborativeevidence is necessary to confirm ASR as a likely cause of this type of cracking.

FIG.22 - Cracking in top cord ofconcrete arch bridge. Whitedeposits of ASR gel and calciumcarbonate exude from cracks. Suchcracking may also develop fromfreezing and thawing, and the whitedeposits may or may not containASR gel. In frost-free climates,ASR is the most probable cause ofthe cracking but corroboratingevidence should be obtained toconfirm its development.

FIG.23 - Bridge column showing crackingassociated with ASR. Predominant cracksare oriented longitudinally, but areconnected in irregular pattern by shorttransverse cracks and by fine randommicrocracks. White deposits on columncontain ASR gel. Cracking patterns arerelated to the configuration of the embeddedreinforcing steel.



FIG.24 - Bridge columns showinglongitudinal crack at base near slopedconcrete surface of bridge embarkment. Thiscracking could be due to ASR or, forexample, to corrosion of embeddedreinforcing steel. Further investigation,including microscopic examination ofconcrete, is necessary to confirm causes. Inthis case, ASR has developed in theconcrete. In these situations cracking at thebase is more apparent and prevalent than inthe rest of the column due to wicking ofmoisture from underlying soil and splashingby passing vehicles. If chloride deicers areused in the area, ASR cracking will promoteingress of chloride into the concrete andtrigger corrosion of reinforcing steel.

FIG.25 - Cracking associated with ASR inbridge column. Predominant cracks areoriented longitudinally in column, and areinterconnected by short transverse andrandom cracks. Longitudinal cracksoccasionally develop at regular spacings,possibly controlled by location of embeddedvertical reinforcing steel. Drying shrinkagehas probably enlarged cracks.



FIG.26 - Closeup of cracking associatedwith ASR in bridge column. The mostprominent crack is oriented approximatelylongitudinally in the column and usuallydoes not extend along the full length ofcolumn. Finer microcracks interconnect inrandom fashion. Drying shrinkage may havecontributed to cracking shown in photo.

FIG.27 - Cracking associated withASR in wingwall of bridgestructure. Major cracks tend toshow subhorizontal orientation andare more strongly developed atlower levels, where humidity andmoisture are at the highest due towicking effects from soil andshielding from solar drying.Cracking of this type also mayresult from frost action and must becorroborated with other evidence topositively assign ASR as a cause.In climates that are essentiallyfrost-free, ASR is a probable cause.

FIG.28 - Curb section borderingapproach slab to bridge structure.Curb shows distress due to ASR.Displaced wedge-shaped curbsection shows uplift from originalposition. Longitudinal and finerandom cracks are typical distressdue to ASR, but uplift may haveresulted from other causes, such asshifting of entire approach slab.Use such observations only aspossible evidence of ASR.










4. Identification of ASR Gel in Field StructuresReturn to Table of Contents

Introduction

The only indisputable evidence that ASR has developed in concrete is the presence ofASR gel reaction products. In the early stages of reactivity, or under conditions whereonly small quantities are produced, ASR gel is virtually undetectable by the unaidedeye, and revealed only with difficulty by a skillful observer using a microscope.Thus, ASR may go unrecognized in field structures for some period of time, possiblyyears, before associated severe distress develops to force its recognition and structurerehabilitation. In addition, due to the difficulties associated with interpretation offield inspections of distressed concrete, it is often misdiagnosed leading owners toimplement rehabilitation strategies that are ineffective with ASR. It is thereforeimportant to implement procedures and methodology in the field that will successfullydiagnose potential ASR reactivity as soon as possible so proper rehabilitationmethods can be implemented that will be successful in extending the useful life ofconcrete pavement and structures.

Under the SHRP Program, the use of the uranyl (uranium) acetate fluorescencemethod was developed so that it can be utilized to monitor possible ASR prior todevelopment of serious distress. The method, rapid and economical, is described inSection a. below. The method can be utilized both in the laboratory and in the fieldusing portable equipment. While the method has proven useful in screeningdistressed concrete for potential ASR distress, it does present a few issues in itsimplementation which have prevented its widespread use in field inspections. Themethod utilizes a chemical solution which contains a slightly radioactive uraniumisotope. While the level of radioactivity presents minimal risk, its use is regulated bya number of agencies and care must be taken in removing all materials from theinspections that have been in contact with the uranium. Secondly, a portable UV lightbox must be utilized to visualize the test section after treatment with the uranylacetate. A bushhammer fitted to an impact drill is needed to expose the surface. Avacuum is needed to collect all contaminated powder and chips. The UV light box,impact drill and vacuum used in the method require electricity, thus making itimperative to have either a source of electricity or a generator available at the site ofinspection.

More recently, due to the difficulties encountered with the uranyl acetate method, theDepartment of Energy (DOE) Los Alamos Laboratories have developed a method


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that is easier to use, only requires easy to handle non-toxic reagents, and achievesvisualization of ASR gel by the naked eye, thus not requiring a special light box. Thismethod is described in Section b. below. This method is still experimental and not yetavailable in the marketplace. It is presented here because results to date are verypromising and it is expected the method will be marketed in the form of a test kitwithin the next six months. Check back with this site for further information.

a. Uranyl Acetate Procedure(Brief Summary of AASHTO T 299)

Uranyl Acetate Solution

Use the following steps to prepare the uranyl acetate solution for ASR gelrecognition. Be sure to wear protective eye wear (goggles or glasses) and rubbergloves while mixing the solution.

1. Prepare dilute acetic acid solution by adding 5 mL of glacial aceticacid to deionized or distilled water to make up 100 mL of solution.

2. Add 5 g of uranyl acetate powder to the dilute acetic acid solution.Warm, but do not boil, to dissolve the powder.

3. Store in closed plastic bottles. Reagent solution has shelf life of a yearor more.

Procedure

This procedure can be used on any concrete surface to identify ASR gel. However,experience has shown that formed or sawed surfaces that have been exposed for yearsare not always satisfactory. Thus, it is best to use surfaces that are newly formed,such as fresh fractures, cores, and ground or sawed surfaces. In the field this can beaccomplished by the use of a bushhammer, or by coring and fracturing a core.Thereafter, proceed with the following steps.

Step 1

Prepare surface to be examined as follows :

Old Formed, finished, or wearing surface :Use grinding wheel on electric drillor other means, such as a bush hammer, to grind off up to ¼ inch of concrete.Rinse with tap water.

1.

Fractured surface :Break off piece from concrete structure or fragment andrinse freshly fractured surface with tap water.

2.

New concrete core :Rinse off cylindrical surfaces after core retrieval. If corehas been dried, rewet and wash with tap water, if necessary, to remove solidsfrom coring slurry.

3.

Step 2

Put on protective eyewear (goggles or glasses) and rubber gloves. Apply uranylacetate solution from plastic squeeze bottle or sprayer. Only a momentary application



of solution film is necessary to adequately wet the surface with solution.

Step 3

Allow solution to react for 3 to 5 minutes with any ASR gel that might be present onthe surface. Then rinse surface with water. Remove protective eyewear (chemicalgoggles or glasses) and gloves.

Step 4

Put on UV absorbing protective eyewear. View the concrete surface using UV lightin a darkened room or, when in the field, through viewing openings in a box thatprevents light from reflecting on the concrete surface.

NOTE :

Once treated, the surface can be viewed at later ages without further solutionapplication. However, it is advisable to first rewet the surface with water.

1.

All liquids, powders and surfaces exposed to uranyl acetate, including anyclothes that may have come in contact with the material, should be collectedand disposed of properly according to federal and local rules and regulations.

2.

The pictures below demonstrate how the method is applied in the field for ASRscreening. Note methods used to insure that any material that comes in contact withuranyl acetate is collected for proper disposal.

FIG. 29 - Impact drill, UV-lightviewing box, and vacuum used inpreparing and removing testsurfaces. Drill is fitted withbushhammer.



FIG. 30 - Bushhammered surfacerinsed and ready for uranyl acetateapplication.

FIG. 31 - Drops of uranyl acetatesolution being applied to verticalsurface using plastic squeeze bottle.Note cloth held against concretebushhammered surface to absorbexcess solution.

FIG. 32 - Bushhammering treatedsurface to remove uranyl acetatecontaminated layer. Note hoseattachment to vacuum to collectpowder and chips generated bybushhammering.

Interpretation

The presence of ASR gel will be revealed in UV light by a yellowish-green fluorescentglow. Deposits will be localized in cracks, air voids, certain aggregate particles and,in severe cases, as broad films in aggregate particles and fractured surfaces. Suchfilms on sawed and cored surfaces may reflect smearing during surface sawing orcoring. Fractured surfaces eliminate this effect and most clearly reveal undisturbedASR gel deposits. This smearing is not likely in a bushhammered surface.

Figures 33 through 36 illustrate typical occurrences of ASR gel as seen in ordinaryand UV light. Interpretations are offered of representative occurrences of gel in



distressed concrete.

FIG.33 - Fractured surfaceof concrete pavement coreshowing location ofreactive granite gneissparticles (arrows), asphotographed in ordinarylight. There is no positiveindication of ASR gel onthis surface in ordinarylight.

FIG.34 - Same fracturedsurface shown in Fig. 33after uranyl acetatetreatment. Green andbright yellow areas displayASR gel. Note band ofASR gel along peripheryof granite gneiss particle(arrow) while interior ofparticle is free of reactionproduct. Film of ASR gelhas spread over aboutone-half of surface shown.

FIG.35 - Badly crackedcoarse aggregate andconcrete from pavementshowing severe crackingsimilar to that illustrated inFigs. 4 and 5. Cracking atpavement wearing surfacewas typical of thatassociated with ASR.



FIG.36 - Same field ofview as shown in Fig. 35but photographed in UVlight after treating withuranyl acetate solution.Brown fractured coarseaggregate particle to leftdisplays peripheral greenfilm of ASR gel.Microcracks betweentriangular coarse aggregateparticle to right and brownparticle with peripheralband contain lightgreenish-yellow deposit of ASR gel. Crack with ASR gel extends abovebrown particle and along periphery of triangular particle. Development ofASR is confirmed by these observations.







Handbook for the Identification of Alkali-Silica Re Activity in Highway Structures,Revised Edition

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