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Portland Cement Association Research and Development Bulletin AD114 The Use of Recycled-Concrete Aggregate from Concrete Exhibiting Alkali-Silica Reactivity by David Stark
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Page 1: Portland Cement  · PDF filePortland Cement Association ... en granulats pour nouveau beton. ... Two ASTM cements were blended to as coarse aggregate. The cement with

Portland Cement Association

Research and Development Bulletin AD114

The Use of Recycled-Concrete Aggregate from Concrete Exhibiting Alkali-Silica Reactivity

by David Stark

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KEYWORDS: aggregate, alkali-silica reactivity, cement alkali level, concrete, expansion, fly ash, pavement, recycledconcrete

ABSTRACT: An investigation was made into precautions that were needed to prevent expansive alkali-silicareactivity (ASR) when ASR-affected concrete is recycled as coarse aggregate in new concrete. Cements with alkalilevels of 0,50%, 0.75”/0,and 1.OOO/.equivalent Na20 were used with highly reactive fine and coarse aggregate in originalconcretes that were recycled at ages of two months and at about one-half maximum expansion and near maximumexpansion. New concretes containing recycled concrete as coarse aggregate were made using innocuous fineaggregate and cements with 0.50% or 1.001%cement alkali, with and without fly ash. Test storage in all cases was o~’erwater in sealed containers held at 380C (lOO[’F).Results indicated that excessive expansions due to ASR can developin the new concrete containing the recycled concrete particularly when low alkali cement was used in the originalconcrete and high alkali cement was used in the new concrete. Low lime ASTM Class F fly ash used at a 20% massreplacement level for cement, for the most part, reduced expansions to safe levels. Observations of pavement concreteindicate successful control of potential ASR in ASR-affected concrete recycled as aggregate in which fly ash is includedin the concrete mixture.

REFERENCE: Stark, David, The Use of Recycled-Concrete Aggregate from Concrete Exhibiting Alkali-S ilico Reactivity,Research and Development Bulletin RD114, Portland Cement Association, Skokie, Illinois, U. S. A., 1996.

MOTS CLES: b&on, bdton recycld, cendres volantes, expansion, granulats, niveau d’alcali du ciment, pavages,r~activitd alcali-silice

RESUME: Une recherche a 6te faite sur les precautions h prendre pour pr6venir l’expansion due ~ la rdactivite alcali-silice lorsque l’on recycle du bdton, affecte de cette reaction, en granulats pour nouveau beton. Des ciments avec desniveaux d’alcalis de 0.50”/., 0.75~0 et 1.OOO/.(en equivalent NazO) ont ete combines avec des granulats fins et groshautement reactifs pour produire le beton original qu’on a ensuite recycle a deux mois d’i?ige,a la moitie de l’expansionmaximum eta expansion maximum. Les nouveaux betons contenant du b&on recycle pour les gros granulats ont eter6alises avec des sables neutres et des ciments avec teneur en alcali de 0.500/.et 1.OOO/.,avec ou saris cendres volantes.Dans tous les cas, les echantillons ont &e conserves clans I’eau, clans des contenants scenes et Aune temperature de38°C (1OO”F).Les rdsultats indiquent qu’une expansion excessive due a la reactivity alcali-silice peut se developperclans les nouveaux bdtons contenant du bdton recycld particuli&-ement lorsqu’un ciment Afaible teneur en alcali dtaitutilise clans le beton original et une haute teneur en alcali etait utilisee clans le nouveau bdton. Dans la plupart des cas,une cendre volante ASTM classe F ~ faible taux de chaux utilisde a un taux de replacement du ciment de 20% (enmasse) a rdduit l’expansion a un niveau sdcuritaire. L’observation de b&ons de pavage indique que l’on peut contri?deravec succbs la reaction potentielle alcali-silice clans des b&ons contenant des granulats en beton recycle deja affectespar la reaction lorsque l’on y ajoute des cendres volantes.

REFERENCE: Stark, David, The Use of Recycled-Concrete Agg~egate from Concrete Exhibiting Alknli-Silico Rcflctivity,Research and Development Bulletin RD1 14, Portland Cement Association [Utilisation de granulats de bdons recyckprovenant d’ztn bdton aj$ectd par la rdactiuitd alcali-silice, Bulletin de Recherche et Developpement RD114, Association duCiment Portland], Skokie, Illinois, U. S.A., 1996.

Cover Illustrations:Top Lefti Illustration of cross-section of concrete containing recycled concrete aggregate (#65256).

Bottom Left: Illustration of deterioration due to alkali-silica reactivity in a highway pavement (#65257).

Righk Broken highway pavement being hauled away to be made into recycled aggregate for new concrete pavement (#42534)

PCA R&D Serial No. 2033

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PCA Research and Development BulletinRD114

The Use of Recycled-Concrete Aggregate fromConcrete Exhibiting Alkali-Silica Reactivity

by David Stark”

INTRODUCTION

Recycling existing concrete for use asaggregate in new construction hasgained attention in recent years be-cause of increased costs of disposal ofold concrete and greater costs of vir-gin aggregate to the job site. How-ever, when the old concrete is re-cycled as aggregate in new concrete,durability concerns will still exist withthe new concrete. This has been aparticular issue in pavement construc-tion where such factors as freezingand thawing and alkali-silica reactiv-ity (ASR) in old concrete might causeprogressive deterioration of new con-crete containing the recycled concreteas aggregate.

This report describes an investi-gation into the importance of pos-sible continued ASR as it affects newconcrete containing recycled concreteas aggregate. Special reference is giventohighwaypavernent where recycledconcrete, in several instances, has beenused as coarse aggregate.

BACKGROUND

As ASR proceeds in concrete, bothalkali (sodium and potassium) andpotentially reactive silica and silicateare consumed while, in highwaystructures for example, practically un-limited moisture will be available for

absorption and swelling of ASR gelreaction products. Since excessivequantities of potentially reactive silicaor silicate relative to alkali normallyare present in concrete, the factor lim-iting expansive ASR probably will bedepletion of alkali available in suffi-cient concentration in the pore solu-tion in the concrete to produce poten-tially expansive reaction product. Be-

cause some alkali combined in the re-action product may be regeneratedinto the pore solution by replacementby dissolved calcium, it becomes diffi-cult to determine by pore solutionanal ysis whether the potential remainsfor continued expansive reactivity. Inaddition, diffusion and interaction of“new” pore solution in recycled con-crete is not readily, if at all, predict-able. Thus, determining expansion re-sulting from ASR is the preferredmethod of evaluation of continuingexpansive reactivity.

SCOPE OF THE TESTPROGRAM

Tests carried out in this investigationconsisted of fabricating new concreteprisms containing coarse aggregatemade from old concrete previouslytested to certain levels of expansion.The original concretes were made us-ing highly reactive fine and coarseaggregate in combination with ce-

ments with 0.50”/0,().750/.,and 1.007.alkali as equivalent Na20. The con-cretes were cast as 150 x 300-mm (6x12-in.) cylinders for subsequent pro-cessing to provide the recycled coarseaggregate, and as 75 x 75 x 275-mm (3x 3 x 11-1 /4-in.) concrete prisms forexpansion determinations for the fullduration of the 48-month test period.At two months and at expansion lev-els corresponding to approximatelyone-half and to essentially maximumexpansion, a sufficient number of cyl-inders were crushed, processed, andused as coarse aggregate in sets ofconcrete prisms made for subsequentexpansion determinations. Theseprisms thus contained the recycledconcrete as coarse aggregate and aknown innocuous unused fine aggre-gate. The recycled aggregate obtainedfrom each original concrete mixturewas used with high- and low-alkalicements, both with and without a 200/0mass replacement of the cement by alow-lime ASTM Class F fly ash withknown capability to prevent expan-sion due to ASR. Comparator read-ings then were taken on the new con-crete prisms up to a test age of 46

* Senior Principal Scientist, Materi-als Research and Consulting, Con-struction Technology Laboratories,Inc., 5420 Old Orchard Road,Skokie, Illinois 60077-1083. Phone:847-965-7500, Fax 847-965-6541.

ISBN 0-89312-145-2

0 Portland Cement Association 1996 1

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The Use of Recycled-Concrete Aggregate from Concrete Exhibiting Alkali-Silica Reactivity

months. For prisms containing re-cycled-concrete aggregate, the testperiod was shortened by two monthsor by the number of months requiredto reach the targeted 50% and maxi-mum expansion levels. Despite thisshortened test period, meaningfultrends were observed for all concretes.

Table 1. Composition and Properties of Portland Cements and FlyAshes Used in this Investigation

Analyte Cement Fly ash1.00”/0 ().i’5°/o o.so~o JAlkali Alkali Alkali

CaO

Si02Al203Fe203Si02+A1203

+Fe20s

S03

MgO

Total Na20Total K20Total Na20

equivalent

Avail. alkali asNa20 equivalent

Free CaOMoisture contentLOI

Insoluble residue

C3SC2SCjAC4AFBlaine m2/kgNo. 325 sie;e, 7.

retained

Pozzolanic activityindex

Portlandcement, O/.Lime, psi

62.11

20.354.483.32

2.78

4.03

0.420.881.00

1.18

0.12

5318710

383

62.99

20.604.593.34

2.66

3.02

0.300.680.75

1.16

0.14

5418710

378

63.94

20.864.703.36

2.55

2.01

0.180.490.50

1.15

0.16

54188

MATERIALS both the original concrete and the newconcrete containing recycled concrete

Two ASTM cements were blended to as coarse aggregate. The cement withprovide the required alkali contents 0.75% equivalent Na20 was used onlyfor all the concrete mixtures. Charac- in the original concrete.teristics of the test cements are given The highly reactive coarse and finein Table 1. The cements with 1,00% or aggregates were from New Mexico0.507. equivalent Na,O were used in and contain 10 to 200/.reactive glassy

to cryptocrystalline volcanic materialof rhyolitic to andesitic composition.More slowly reactive chert was presentin much smaller amounts. These ag-gregates are known to be deleteriouslyreactive with portland cements withequivalent NazO contents as low as0.50 to 0.60°/0. Other components ofthe aggregate are innocuous granitic-textured rock types, limestone, quartz,and feldspar.

The innocuous fine aggregate usedin mixtures with recycled concrete ascoarse aggregate was a well roundedglacial material from Elgin, Illinois. Itconsisted of about 50~0 dolomite, 40~o

quartz and feldspar, and minoramounts of limestone, quartzite, crys-talline basalt, and granitic-texturedmaterial.

A fly ash meeting ASTM Class Frequirements was used in some of thenew concrete prisms, Characteristicsof this material are given in Table 1.Itshould be noted that this is a low limefly ash containing 5.47% calcium ox-ide. A low lime content is a desirablecharacteristic of the fly ash because itsuse at a 20% dosage rate should sig-nificantly reduce lime-silica ratios ofthe calcium silicate hydration productof the cement plus fly ash, therebyproviding greater capability to retainalkali from the pore solution in theconcrete and minimizing expansiondue to ASR.l

10374

5.10

46.1020.1016.9683.16

1.36

1,33

0.532.232.00

0.65

1.490.154.86

37514.4

90920

MIXING AND CASTINGPROCEDURES

All original concretes were mixed in a0.1 12rnq(4 ft3)rotating pan-type mixeron a 3-3-2, mix-rest-mix cycle. Suffi-cient material was batched and mixedto provide concrete for three 75 x 75 x

2

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PCA Research and Development BulletinRD114

286-mm (3x 3x11-1 /4-in.) prisms, and24 150x 300-mm (6 x 12-in.) cylinders.The latter were used to supply recycledconcrete for the coarse aggregate in thenew concrete. After casting, all speci-mens were cured in the molds for oneday under damp burlap covered withpolyethylene sheeting. All batching,mixing, casting, and storage in themolds was carried out at 23°C (73’’F).After one day all specimens werestripped from the molds and trans-

ferred to test storage over water insealed containers at 38°C (1OO”F).Justprior to transfer, comparator read-ings were taken on the concrete prismsto serve as the basis for calculatingsubsequent expansions during teststorage.

At a test age of two months, andat the appropriate test time based onexpansion levels of the three compan-ion prisms, six concrete cylinders wereremoved from test, allowed to dry for

Table 2. Aggregate Gradings for Concrete Mixtures

Reactive coarseRecycled coarse

Sieve size and fine aggregate,and innocuous

70fine aggregate,

Y.

Coarse aggregate--

31.8 mm to 19.0 mm 18 18

(1 ~in. to ~in.)

19.0 mm to 9.5 mm 60 60

(~in. to ~in.)

9.5 mm to 4.75 mm 20 22

(~in. to No. 4)

4.75 mm to 2,36 mm 2 0(No. 4 to No. 8)

Fine aggregate

9.5 mm to 4.75 mm 4 2

(#in. to No. 4)

4.75 mm to 2.36 mm 12 16(No. 4 to No. 8)

2.36 mmto 1.18 mm 10 20(No. 8 to No. 16)

1.18 mmto 600pm 20 23

(No. 16 to No. 30)

600 ~m to 300 ~m 34 25

(No. 30 to No. 50)

300 pm to 150 ~m 17 12

(No. 50 to No. 100)

-150pm 3 3

(- No. 100)

one day at 38°C (1OO”F)and 30°/0RH,then crushed to provide the requiredquantity and gradation of recycled-concrete coarse aggregate. None ofthis aggregate was subjected to wash-ing during processing according tocommon commercial practice. Thus,alkali present in the pore solution inthe original concrete also was presentin the recycled concrete used as coarseaggregate in the new concrete.

Three companion 75 x 75 x 286-mm (3x3x 11-1/4-in.) concrete prismswere cast using only recycled con-crete as coarse aggregate, togetherwith natural Elgin fine aggregate, Flyash was incorporated into selectedmixtures at the 200/.dosage level. Thesame procedures were used forbatching, mixing, casting, and stor-age in the molds as described previ-ously. Again the initial comparatorreadings were taken just prior to trans-fer to storage over water in sealedcontainers at 38°C (1OO”F).As statedpreviously, the initial set of prismscontaining recycled concrete as ag-gregate was fabricated two monthsafter casting the original concretes.Subsequent sets were fabricated whenthe original concretes reached a pro-jected 50°/0and 900/. to 100% of themaximum expansion, based on pre-vious experience using other samplesof aggregate from this source.

TEST REGIME

All concrete specimens were storedunder ASTM C 227 test conditions.That is, immediately following strip-ping from the molds and the initialcomparator reading, the specimenswere placed over water in sealed con-tainers stored at 38°C (1OO”F).Furtherreadings were taken periodically overa period up to 48 months. A test fail-ure criterion of O.lOO/Oexpansion wasused as suggested for mortar bars inthe Appendix of ASTM C 33. In thepresent series, this expansion levelwas applied because it has been ob-served microscopically by the writer

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The Use of Recycled-Concrete Aggregate from Concrete Exhibiting Alkali-Silica Reactivity

Table 3. Proportions for Concrete Mixtures, kg/m3 (lb/yd3)

Component Original mixtures Recycled mixtures

Without fly With fly ash Without fly With fly ashash ash

Cement 356 285 356 285(600) (480) (600) (480)

Fly ash —

(:0) – (1!0)

Coarse aggregate 1130 1130 —

(1905) (1905) –

Recycled concrete — — 1016 1016(1712) (1712)

Fine aggregate 706 706 706 706(1190) (1190) (1190) (1190)

Water 167 161 171 171(281) (272) (288) (288)

that cracks attributed to ASR are coarse aggregate and cements with Here, expansions were reduced to be-present in either mortar or concrete bythe time this expansion level is reached.

TEST RESULTS

Results for all tests are plotted in Figs.1 through 17 as expansion versus timefor the various combinations of ce-ment, fly ash, and unused and recycledconcrete aggregate.

Results for ConcreteContaining UnusedAggregate

Fig. 1 shows 48-month expansions ofconcrete containing unused fine and

* From this point onward, concretesmade with cement containing 1.OOOAI

alkali as equivalent Na20 will bereferred to as high-alkali concrete.Those containing cement with().75”/.alkali will be referred to asmedium-alkali concrete, and thosemade with cement with 0.50% al-kali will be referred to as low-alkaliconcrete.

0.50, 0.75~;r l~00% alkali as equivalentNazO. Curves in this figure illustratethe reactive nature of the aggregateand the dependence of expansion onthe alkali content of the cement. Asexpected, the greatest expansions(0.35%) were reached by the mixturecontaining cement with 1.OOO/.alkali. Itshould be noted that, for all practicalpurposes, maximum expansions werereached within 24 months for mix-tures made with cements with 1.00%or 0.75% alkali as equivalent Na20. Forthe mixture containing the cement with0.500/.alkali, expansions reached only0.05’%. at about 42 months. This rela-tively low expansion level has beenfound to be associated with the earlystages of ASR in other work by thewriter.

Results for MortarContaining UnusedAggregate and Fly Ash

The effectiveness of the fly ash in re-ducing expansions due to ASR in C227 mortars containing the highly re-active fine aggregate is shown in Fig. 2.

low the-suggested ASTM C 33 testcriterion of 0.10%, when the dosage offly ash was in the range of 157. to 200/.for cements with 0.500/. and 1.00%equivalent Na20 respectively. Ac-cordingly, the 20% dosage rate wasselected as sufficient to safely controlexpansion due to ASR in the test con-cretes.

Results for ConcreteContaining RecycledConcrete as CoarseAggregate*

Examples of results of recycling po-tentially reactive concrete into coarseaggregate for new concrete are shownin Figs. 3 through 5. Here, cumulativeexpansions for new concrete contain-ing recycled concrete as coarse aggre-gate are plotted from the age andlevel of expansion at which recyclingof the original concrete was done. Forexample, Fig. 3 (solid-dot graph line)shows that about 0.24~0 real expan-sion (0.32% original concrete expan-sion plus ().24~0new concrete expan-

4

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PCA Research and Development Bulletin RD114

0.40

II

0.30

0.00

1Cement alkali content

~ 1.OOO/OAlkali I1? I ~ 0.750/0Alkali

~ 0.50°AAlkali I

o 6 12 18 24 30 36 4 4Time, months

Fig. 1. Expansion of concrete containing unused aggregate andcements with different alkali contents. Tests were conducted underASTM C227 storage conditions.

0.70,

4

0.60,,

0.30

().0() ~o 10 20 30 40

Fly ash dosage,

Fig. 2. Expansion of mortars containing different dosages of fly ashand cements with alkali contents 0.50?40and 1.00Y0. Storage wasunder ASTM C227 test conditions.

sion equals 0.56°/0cumulative expan-sion) developed whenhigh-alkali con-crete was recycled at 15 months intonew high-alkali concrete with no flyash, even after no further expansiondeveloped in the original concrete.The result indicates that ASR in theoriginal concrete consumed sufficientalkali to virtually terminate furtherexpansion, and that the introductionof additional alkali in the new high-alkali concrete reinitiated expansiveASR, despite much reduced quanti-ties of potentially reactive material inthe aggregate (only the coarse aggre-gate was reactive in the new con-crete).

Fig. 4 illustrates the effects whenlow-alkali concrete is recycled intohigh-alkali concrete with no fly ash.In this case, little if any ASR occurredin the original concrete prior to recy-cling. Major expansion developed inthe new concrete, probably as a resultof the use of high-alkali cement incombination with only slightly re-acted recycled aggregate from theoriginal low-alkali concrete. Resultsin Fig. 5 indicate that a 20% dosage offly ash in new high-alkali concrete,which contained recycled low-alkaliconcrete as coarse aggregate, reducedexpansions to approximately 0.12°/0.This is greater than subsequent ex-pansion of the original concrete madewith low-alkali cement.

These three examples are illus-trated in the above fashion to providesome indication of the nature of thetest results. Comparisons for each testcombination are more clearly seen inthe following discussions where ex-pansions are plotted from “zero” timeand expansion level.

High-Alkali ConcreteRecycled into High-AlkaliConcrete With and WithoutFly Ash

Fig. 6 presents results in which origi-nal high-alkali concrete was recycledinto new high-alkali concrete with-

5

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The Use of Recycled-Concrete Aggregate from Conc~ete Exhibiting Alkali-Silica Reactivity

out fly ash. In this combination, newconcrete expansions were lower thanthose for the original concrete (0.35%)but still in the range of 0.10 to 0.25%,which is considered excessive, Amongthe three times of recycling, the lowestexpansion developed for recycling oforiginal concrete at two months. Theother two ages, at about half and atmaximum expansion, showed expan-sion levels that were greater than thosefor prisms with two-month recycledconcrete. Reasons for this differenceare not fully known, but it maybe due,in part, to greater ASR after the firsttwo months, with accompanyingopening or cracking of reactive par-ticles and subsequent penetration ofnew alkali pore solution into the re-cycled concrete. It also is possible thatthe additional alkali may alter exist-ing ASR gel to render it more expan-sive in the new concrete. In any case, itappears that high-alkali cement shouldnot be combined with previously re-acted concrete recycled as coarse ag-gregate in new concrete, without theaddition of a suitable fly ash.

When a 20% dosage of fly ash wasused, maximum expansion reachedonly about O.lOO/.,as shown in Fig. 7.Expansions were reduced by about75% to less than 0.10% for the newconcrete containing original concreterecycled at about one-half and at maxi-mum expansion. New high-alkali con-crete containing original concrete re-cycled at two months expanded toabout the same level as the new con-crete made without fly ash. That is, theuse of fly ash appeared to have nomeaningful effect on reducing expan-sions in the new concrete when theoriginal concrete was recycled at twomonths, This may reflect the relativelylow margin for reduction of expan-sion given the short test time prior torecycling. Collectively, the results in-dicate that cement-fly ash hydrationproducts effectively reduced alkaliconcentrations in the pore solutions,thereby effectively reducing expan-sions due to ASR.

0.60

0.50

0.40

0.30

0.20

0.10

0.00

10.24% real expansion \

I 4 0.230/.real expansion,

t J=7 “-” ‘1.

-0- Original concrete (1.0% alkali)

lx I + Recycleat2 I1/ 1“~ Recycle at about halt maximum expanaion

It ~ Recycle at about full maximum expanaion

Iti ‘:’ ‘ ‘0,1 O% real expansion

If I

o 6 12 18 24 30 36 42 48Time, months

Fig. 3. Cumulative expansions for mixtures in which originalhigh-alkali concrete was recycled as coarse aggregate in newhigh-alkali concrete with no fly ash. Cumulative expansions for newconcrete containing recycled concrete as coarse aggregate areplotted from the age and level of expansion at which recycling oforiginal concrete was done. The old and new concrete expansionvalues are combined to provide a cumulative value. Time zero(actual) expansions are shown in Fig. 6.

0.40T

0.00

I / i

f-” 0.22% real expansion /’-’--

/i~ Original concrete (0.5”/. alkali)

~ Recycle at 2 months

II /1~ Recycle at about half maximum expanaion

o 6 12 18 24 30 36 42 48Time, monthe

Fig. 4. Expansions for mixtures in which original low-alkali concretewas recycled as coarse aggregate in new high-alkali concrete with nofly ash. Cumulative expansions for new concrete containing recycledconcrete as coarse aggregate are plotted from the age and level ofexpansion at which recycling of original concrete was done. The oldand new concrete expansion values are combined to provide acumulative value. Time zero (actual) expansions are shown in Fig. 14.

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PCA Research and Development Bulletin RD114

0.40

3c.-,gl

5~ 0.30 I

0.20

0.10

0.00

-U_ Original concrete (0.5% alkali)

~ Recycle at 2 months

11~ Recycle at about half meximum expansion

I 0.1 4% real expansion\

O.11 Y. real expansion

i 6 12 18 24 30 36 42 48

Time, months

Fig. 5. Expansions for mixtures in which original low-alkali concretewas recycled as coarse aggregate in new high-alkali concrete with flyash. Cumulative expansions for new concrete containing recycledconcrete as coarse aggregate are plotted from the age and level ofexpansion at which recycling of original concrete was done. The oldand new concrete expansion values are combined to provide acumulative value. Time zero (actual) expansions are shown in Fig. 15.

} 0201r~-U- Original concrete (1.0% alkali)

~ Recycle at about half maximum expension&

I/~ Recycle at about full maximum expansion

‘ 0“’0 ~0.00

i 6 12 18 24 30 36 42 48

Time, months

Fig. 6. Expansions for mixtures in which original high-alkali concretewas recycled as coarse aggregate in new high-alkali concrete with nofly ash.

High-Alkali ConcreteRecycled into Low-AlkaliConcrete With and WithoutFly Ash

Fig. 8 summarizes results for high-alkali concrete recycled into new low-alkali concrete without fly ash, In thisseries of tests, the low-alkali cementin the new concrete was effective inreducing expansions to safe levels(less than 0.10%) when recycling ofthe original concrete was done atabout half and near maximum expan-sion. Recycling the original concreteat two months resulted in slightlygreater expansions which, however,were still in the range of 0.10 to 0.15Y0.This is well below the 0.350/. maxi-mum expansion for the original con-crete. The data thus indicate that theuse of low-alkali cement greatly re-duced expansion due to ASR whenthe original concrete that was recycledpreviously exhibited deleteriousASR.This reduction may as well be attrib-uted to consumption of alkali in pre-vious ASR in the original concrete.

Results for high-alkali concreterecycled into low-alkali concrete con-taining fly ash are shown in Fig. 9.Here expansions were reduced stillfurther than those where low-alkalicement was used in new concretewithout fly ash. When fly ash wasused in the new concrete, expansionswere reduced to less than ().050/.,re-gardless of the level of expansion pre-viously reached in the original con-crete.

Medium-Alkali ConcreteRecycled into High-AlkaliConcrete With and WithoutFly Ash

Fig. 10 presents results for originalmedium-alkali (0.75°/0 equivalentNazO) concrete recycled into newhigh-alkali concrete with no fly ash.Here expansions either approxi-mately equaled or greatly exceededexpansions for the original concrete.

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The Use of Recycled-Concrete Aggregatefiom Concrete Exhibiting Alkali-Silica Reactivity

New concretes that exceeded expan-sions of the original concrete werethose containing concrete recycled asaggregate at two months, and at abouthalf the maximum expansion of theoriginal concrete. Expansions wereessentially the same for new high-alkali concrete containing concrete re-cycled at approximately maximumexpansion of the original concrete. Thegreater expansions for the two newconcretes containing concrete recycledas coarse aggregate at two monthsand about one-half the maximum ex-pansion are possibly due to more al-kali being available from the originalconcrete, in addition to that introducedin the new concrete.

Comparison of data in Fig. 11 in-dicates that all high-alkali concretemixtures containing concrete recycledas coarse aggregate and made with flyash produced expansions less thanthe original medium-alkali concrete,regardless of age or of level of expan-sion at which recycling was done.However, expansions of new concretecontaining recycled concrete as coarseaggregate still were between O,10%and 0.150/., This suggests that the flyash in the new concrete greatly re-duced expansions but not to safe lev-els, and that perhaps existing ASR gelin the recycled concrete continued toexpand after pore solutions penetratedinto the recycled concrete aggregatebefore fly ash in the new concretecould reduce the alkalinity of the poresolution in the new concrete to safelevels.

Medium-Alkali ConcreteRecycled into Low-AlkaliConcrete With and WithoutFly Ash

Results for medium-alkali concreterecycled as coarse aggregate in newlow-alkali concrete without and withfly ash are similar, as shown in Figs,12 and 13, respectively. In most casesthe alkalinity of the pore solutionswas sufficiently low to prevent exces-

0.40

I

“ ❑

E 0“30t 7’al0znc-’o 0.20.-mcm:w

0.10

0.00

{Y ~ Original concrete (1.OO/.elkali)

~ Recycle at about half maximum expanalon

—0— Recycle at about full maximum axpanaion

+i

a

I

o 6 12 18 24 30 36 42 48

Time, months

Fig. 7. Expansions for mixtures in which original high-alkali concretewas recycled as coarse aggregate in new high-alkali concrete with flyash.

0.40

I

0.30

0.20

u ❑

/1 ~ Originel concreta (1.O% alkali)

~ Recycla at 2 months

r I ~ Reqfclaatabouthal fmaxim.maxpanaionl

/

~ Racycla at about full maximum expanaion

0.10.B

0.000 6 12 18 24 30 36 42 48

Time, months

Fig. 8. Expansions for mixtures in which original high-alkali concretewas recycled as coarse aggregate in new low-alkali concrete with nofly ash.

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PCA Research and Development Bullefin RD114

0.40

0.30

Ea!t)iinc- 0.200.-

:d

0.10

0.00

/

/

-U- Original concrete (1.OO/.alkali)

~ Recycle at 2 months I~ Recycle at about half maximum axpanaion

~ Recycle at about full maximum expanaion

o 6 12 18 24 30 36 42 48

Time, months

Fig. 9. Expansions for mixtures in which original high-alkali concretewas recycled as coarse aggregate in new low-alkali concrete with flyash.

0.40

I

0.30..E8

Zc“o.- 0.20,,~gu

-Cl- Original concrete (0.75% alkali)

~ Recycle at about full maximum expanaion

0.00i 8 12 18 24 30 36 42 48

Time, monthe

Fig. 10. Expansions for mixtures in which original medium-alkaliconcrete was recycled as coarse aggregate in new high-alkaliconcrete with no fly ash.

sive expansions due to ASR, regard-less of whether fly ash was used inmixtures containing recycled concreteas aggregate. Only in the mixturescontaining concrete as aggregate re-cycled after reaching about half themaximum expansion of the originalconcrete did expansion of the newconcrete approach or slightly exceedO.1O% Reasons for these results arenot readily apparent. However, in theother mixtures, alkalinity of the poresolutions apparently was sufficientlylow to reduce expansions to well be-low the O.lOO/.to 0.200/0expansion forthe original concrete made with themedium-alkali cement.

Low-Alkali ConcreteRecycled as CoarseAggregate into High-AlkaliConcrete With and WithoutFly Ash

Results for low-alkali concrete re-cycled as coarse aggregate in newhigh-alkali concrete with no fly ashare shown in Fig. 14. Here, expan-sions for the new concrete greatlyexceeded those for the original con-crete when recycled at either twomonths or after reaching about one-half the maximum expansion of theoriginal concrete (recycling at aboutmaximum expansion was not donefor original low-alkali concrete be-cause of its extremely low rate of ex-pansion and consequent delay in fur-ther testing). In these cases, expan-sions for the original concrete wereless than about 0.050/0which is wellbelow the O.lOO/.test criterion, andreflects the innocuous behavior of thiscement-aggregate combination. How-ever, after recycling into new high-alkali concrete, expansions of the newconcrete reached about five to eighttimes the expansion of the originalconcrete. This indicates that the higheralkalinity of the pore solution of thenew concrete initiated deleteriousASR involving the recycled aggre-gate, even though the original con-

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The Use of Recycled-Concrete Aggregate from Concrete Exhibiting Alkali-Silica Reactivity

crete failed to exhibit evidence of ex-cessive expansion, This result impliesthat concrete should not be recycledas aggregate unless petrographic ex-amination reveals that ASR has notdeveloped to any degree and that theconcrete does not contain aggregatethat may be potentially deleteriouslyreactive.

When fly ash was used in the newhigh-alkali concrete, expansions werereduced compared to the mixturemade with no fly ash, as shown in Fig.15. However, expansions still reachedseveral times that for the original con-crete and also were somewhat greaterthan the O.lOO/.test criterion. This in-dicates that the fly ash was only mar-ginally, or not at all, able to safelycontrol ASR, in this case, when nodeleterious ASRhad developed in theoriginal low-alkali concrete.

Low-Alkali ConcreteRecycled as CoarseAggregate into Low-AlkaliConcrete With and WithoutFly Ash

Results shown in Fig. 16indicatesimi-lar or somewhat greater expansionsthan the original low-alkali concretewhen it is recycled as coarse aggre-gate into new low-alkali concrete. Inthis case, expansion for new concretereached about 0.10% when recyclingat approximately one-half the maxi-mum expansion of the original con-crete. Recycling at two months re-sulted in expansions of only 0.057.,which is equivalent to that for theoriginal low-alkali concrete. The dif-ference between expansion levels forthese two new concretes is not consid-ered significant since neither exceedsthe 0.10% expansion criterion.

Fig. 17 summarizes results forlow-alkali concrete recycled as coarseaggregate in new low-alkali concretemade with fly ash. Here, expansionsfor both original and new concretewere similar regardless of whetherthe original concrete was recycled at

0.40

0.30

0.20

0.10

0.00

E~ Original concrete (0.75°/0 alkali)

~ Recycle at about half maximum expansion

~ Recycle at about full maximum expansion

o 6 12 18 24 30 36 42 48

Time, months

Fig. 11. Expansions for mixtures in which original medium-alkaliconcrete was recycled as coarse aggregate in new high-alkaliconcrete with fly ash.

Eac1%0.

c-0.-el

1%Q

L5

0.40

~ Original concrete (0.750/. alkali)

0.30

t I~ Recycle at 2 months

~ Recycle at about half maximum axpanaion

I ~ Recycle at about full maximum expansion

0.20

t

0.10.,

0.00

0 6 12 18 24 30 36 42 48

Time, months

Fig. 12. Expansions for mixtures in which original medium-alkaliconcrete was recycled as coarse aggregate in new low-alkaliconcrete with no fly ash.

10

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PCA Research and Development Bulletin RDI 14

0.40TI -Cl- Original concrete (0,75% alkali)

I I ~ Flecycleat2 months I0.30

t 1

~ Recycle at about halt maximum expansion

~ Recycle at about full maximum expanaion

0.20I ‘)-- ‘L-1 x’

0 6 12 18 24 30 36 42 48

Time, months

Fig. 13. Expansions for mixtures in which original medium-alkaliconcrete was recycled as coarse aggregate in new low-alkaliconcrete with fly ash.

0.40-

0.30..

EaoknK- 0.20,.0.-0)c(ua ~ Original concrete (0.5”/0alkali)

i

0.10.. ~ Recycle at about half maximum expansion

0.000 6 12 18 24 30 36 42 48

T&me,months

Fig. 14. Expansions for mixtures in which original low-alkali concretewas recycled as coarse aggregate in new high-alkali concrete withno fly ash.

two months or at about one-half the

maximum expansion, which was taken

to have developed at the age of 15months of the original concrete. Thus,the use of both control measures, flyash and low-alkali cement, was effec-tive in controlling ASR expansion inthe concrete mixture containingrecycled concrete as coarse aggregate.However, the difference in perfor-mance between new concretes madewith low-alkali cement, with and with-out fly ash, appears to be negligibleand of little or no significance.

PAVEMENT PERFORMANCE

Several pavements are currently in ser-vice in the United States in which con-crete previously exhibiting ASR wasrecycled as coarse and fine aggregatefor new pavement. One of these pave-ments, located in Wyoming, has beeninspected in the field, and cores takenfrom the pavement have been exam-ined petrographically for possibleevidence of ASR associated with therecycled concrete aggregate.

The original concrete pavementwas built in the 1970’s under a specifi-cation calling for the use of ASTM low-alkali cement with no mineral admix-tures. By 1976, pavement inspectionand petrographic examination of con-crete cores confirmed the developmentof ASR. Several sources of aggregatewere used along this length of pave-ment, and the severity of distress at-tributed to ASR appeared to vary withthe source. The primary reactive con-stituent in each of the aggregate sourceswas weathered poorly crystalline vol-canic rock of rhyolitic to andesitic com-position, the proportions of whichranged between approximately 5 to10% of the aggregate. Bythemid-1980’s,distress from ASR as well as from traf-fic required that the pavement bereplaced. Accordingly, between 1985and 1988, various sections of the origi-nal concrete were replaced with newconcrete containing low-alkali cement(0.5 to 0.6% alkali as equivalent Na,O),

11

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The LIse ojRecycled-Concrete Aggregatejrom Concrete Exhibiting Alkali-Silica Reactivity

and ASTM Class F fly ash used as a20% mass replacement for cement.Coarse aggregate consisted of abouttwo-thirds recycled concrete and one-third unused limestone. Fine aggre-gate contained approximately 25 to300/. recycled concrete and unusedsand of the same general type thatexhibited ASR in the original con-crete. Pavement thickness was 305mm (12 in. ) with skewed jointsat random spacings less than 6.1 m(20 ft).

A pavement inspection was con-ducted in mid-1993, and cores weretaken at that time for petrographicexamination. The following observa-tions were made:1) 1985 concrete - The wearing sur-

face displayed no evidence ofcracking typically associatedwith ASR. Examination of coresrevealed no evidence of ASR-related distress that may havedeveloped in the new concrete.

2) 1987 concrete - This section ofpavement displayed short,tight, longitudinal cracks alongtransverse joints, and very faintmap cracking in mid-panel ar-eas. Occasional transversecracks also occur at mid-panellocations. Cores revealed noevidence of ASR that may haveformed in the new pavementconcrete. A few microcracksobserved in coarse limestoneparticles extended into sur-rounding mortar. Several filmsof glassy ASR gel partially lineda few entrapped air voids. Sur-face cracks that were observedin the field inspection extendedonly to depths of about 12 to 30mm (1/2 to 1-1/4 in.).

3) 1988 concrete - No abnormalcracking was observed at thewearing surface during the fieldinspection. Also, petrographicexamination of cores revealedno abnormal microcracking norASR gel.

In summary, after six to nine yearsof service, only very limited evidence

0.40

I

II I

~ original concrete (0.50/. alkali)0.30

~ Recycle at 2 monthe ica I ——.—— Recycle at about halt maximum expansion0$ns-0 0.20.-0)RQ I‘0’01z2212iz2

0.000 6 12 18 24 30 36 42 48

Time, months

Fig. 15. Expansions for mixtures in which original low-alkali concretewas recycled as coarse aggregate in new high-alkali concrete with flyash.

0.40T

,0301~-Cl- Originel concrete (0.50/. alkali)

~ Recycle at about halt maximum expansion

c-0.-0)

0.20cgu I

; 6 12 18 24 30 36 42 48

Time, months

Fig. 16. Expansions for mixtures in which original low-alkali concretewas recycled as coarse aggregate in new low-alkali concrete with nofly ash.

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PCA Research and Development Bulletin RD114

0.40-

0.30..

0.20..

+3- Original concrete (0.5% alkali)

~ Recycle at 2 months

~ Recycle at about half maximum expanaion

c1 6 12 18 24 30 36 42 48

Time, months

Fig. 17. Expansions for mixtures in which original low-alkali concretewas recycled as coarse aggregate in new low-alkali concrete with flyash.

of ASR was found that might havedeveloped in the new concrete con-tainingASR-affected recycled concreteas aggregate . Thus far, this findingsubstantiates the laboratory findingof apparent elimination of expansiveASR when low-alkali cement with a20% dosage of low lime fly ash is used.

DISCUSSION

This investigation concerned the de-velopment of expansive ASR in origi-nal concrete that was later recycled ascoarse aggregate, and precautions re-quired to prevent its developmentwhen used in new concrete. Originalconcretes made with unused but po-tentially reactive aggregate and ce-ments with alkali contents of 0.50,0.75, or 1.00% equivalent NazO wereprocessed and used as recycled coarseaggregate in new concrete containingcements with 0.50 or 1.007. equiva-lent Na,O, both with and without flyash. The original concrete was re-cycled at an age of two months and atages of about one-half and near maxi-mum expansions.

Results indicate that recycled con-crete used as coarse aggregate re-

tained potential for continued ASR,and that resulting expansion dependson the alkali content of the cement inthe new concrete and the presence offly ash. It appeared that the factorlimiting expansion in the original con-crete was the availability of alkali (hy-droxyl ion concentration) in the poresolution, and that the reintroductionof alkali from cement used in makingthe new concrete reinitiated expan-sive ASR. This is best illustrated inFigs. 3 and 4, where major expansiondeveloped in the new concrete withthe use of cement with 1.OOO/Oequiva-lent alkali after further expansion es-sentially ceased when high-alkali ce-ment was used in the original con-crete. Also, essentially no expansiondeveloped when low-alkali cementwas used in the original concrete.These results appear to indicate thatunreacted but potentially reactiveaggregate still remained in the origi-nal concrete at the time of recycling.

In the time frame of this investi-gation, the maximum level of expan-sion reached in the original concretedepended on the alkali content of thecement as would be expected. Expan-sions reached in the new concrete

made with recycled concrete as coarseaggregate but without fly ash alsodepended to a major extent on thealkali content of the cement, regard-less of the alkali content of the cementin the original concrete. Again, thisfinding, as expected, provided evi-dence that significant amounts ofunreacted but potentially reactivenatural aggregate remained in there-cycled concrete. In this respect it alsois possible that some reaction betweenalkalies introduced in the new con-crete may have reacted with preexist-ing ASR gel to increase expansions.This was not investigated inthisstudy.

Among the new concretes madewithout fly ash, only those contain-ing low-alkali recycled concrete asaggregate and made with low-alkalicement met the O.lOO/.maximum ex-pansion criterion used in these tests.All other new concretes made with-out fly ash exceeded this criterion tovarying degrees, generally, by increas-ing amounts as cement alkali levelincreased in the new concrete. Theimportant point from this finding isthat even though original concrete ina field structure such as pavementmight not exhibit ASR at the time ofrecycling, it still could produce exces-sive expansions due to ASR in newconcrete containing the recycled con-crete as aggregate if special precau-tions are not taken to prevent thereaction. In this respect, petrographicexamination of the original concreteshould be done to determine if poten-tial for ASR exists in the new concreteprior to recycling,

Using fly ash in new concretecontaining recycled concrete as coarseaggregate reduced expansions in allcases compared with companion mix-tures without fly ash. As expected,the largest reductions occurred fornew high-alkali concretes, regardlessof the alkali content of the cements inthe original concrete. In most caseswhere high-alkali cement was usedwith fly ash in the new concrete, ex-pansions were reduced to below oronly slightly above (up to about 0.150/0

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The Use of Recycled-Concrete Aggregate from Concrete Exhibiting Alkali-Silica Reactivity

expansion) the test criterion of O.1O%.Where low-alkali cement was usedwith fly ash in the new concrete, ex-pansions in all cases were reduced to,or well below, the O.100/. criterion.Thus, the use of certain fly ashes withlow- or high-alkali cement appearedto be the surest way to reduce to safelevels expansions of new concrete con-taining recycled concrete as aggre-gate. The exact reasons why the flyash was unable to reduce expansionsof all mixtures of new concretes areuncertain, but it maybe related to thefact that the recycled concrete aggre-gate was produced and introducedinto the new mixture without wash-ing. This would allow the relativelyhighly alkaline solution of the newfresh concrete to be absorbed morereadily by the recycled aggregate be-fore appreciable reaction of the flyash. This would temporarily estab-lish a condition similar to that if thefly ash had not been included as acomponent of the new concrete mix-ture.

Observations of the Wyomingpavement that contain ASR-affectedrecycled concrete as aggregate thusfar agrees with the laboratory find-ings. That is, the combination of low-alkali cement plus fly ash has success-fully controlled deleterious ASR inrecycled concrete used as aggregatein new concrete. Whether low-(< 0.60%) alkali cement would havebeen required in the pavement is notknown since high-alkali cements werenot used. The only occasional appear-ance of very faint, short longitudinalcracks at transverse joints is sugges-tive of very limited ASR, thus endors-ing the use of fly ash in the pavement.

CONCLUSIONS

Based on observations in this investi-gation, using highly reactive aggregate,the following conclusions are drawn:1.

2.

3.

4.

5.

Recycled concrete used as coarseaggregate in new concrete pos-sesses potential for ASR in thenew concrete if the original con-crete contained aggregate thatwas susceptible to ASR.The alkali content of the cementin the original concrete whereexpansion due to ASR developedhad little bearing on expansionsdue to ASR in new concrete con-taining the original concrete asrecycled coarse aggregate.The alkali content of the cementin the new concrete containingrecycled concrete as coarse ag-gregate had a significant effecton subsequent expansions dueto ASR. However, the use of low-alkali cement without fly ash didnot always reduce expansionsdue to ASR to safe levels.The use of a low-lime ASTMClass F fly ash in new concretecontaining recycled concrete ascoarse aggregate greatly reducedexpansions due to ASR in thenew concrete. However, to bringexpansions to less than the testcriterion, without exception, alsorequired the use of low-alkalicement with the fly ash. It is notcertain whether such stringentmethods would be required forother, less reactive, recycled con-cretes used as coarse aggregate.The pavement engineer shouldnot assume that, because expan-sive ASR did not develop in origi-nal concrete to be recycled asaggregate, it wiIl not develop inthe new concrete, Petrographicexamination of the original con-crete is recommended in thisjudgment.

ACKNOWLEDGMENT

The research reported in this paper(PCA R&D Serial No. 2033) was con-ducted at Construction TechnologyLaboratories, Inc. with the sponsor-ship of the Portland Cement Associa-tion (PCA Project Index No. 89-03).The contents of this paper reflect theviews of the author, who is respon-sible for the facts and accuracy of thedata presented. The contents do notnecessarily reflect the views of thePortland Cement Association.

REFERENCES

1. Bhatty,M.S.Y., “MechanismsofPozzolanic Reactions and Con-trol of Alkali-Aggregate Expan-sion,” Cement, Conc~ete and Ag-gregates, Vol. 7, No. 2, Ameri-can Society for Testing andMaterials, West Conshohocken,Pennsylvania, pp. 69-77,1985.

14

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Metric Conversion Table

Following are metric conversions of the measurements used in this text,

They are based in most cases on the International System of Units (S1),

1 in.

1 sq in.

1 ft

1 Sq ft1 sq ft per gallon

1 gal

1 kip = 1000 Ibf

1 lb

1 lb per cubic yard

1 psf1 psi

No. 4 sieveNo. 200 sieve

1 bag of cement (U. S.)1 bag of cement (Canadian)

1 bag per cubic yard (U. S.)

deg. C

= 25,40 mm

= 645.16 mmz

= 0.3048 m

= 0.0929 m’= 0,0245 m2/L

= 3,785 L= 4.448 kN

- 0.4536 kg—

= 0.5933 kg/m3

= 4.882 kglm’- 0.006895 MPa—

. 4,75 mm

. 75 mm

= 94 lb = 42,6 kg

=881b =40kg= 55.8 kg/m3

= (deg. F - 32)/1.8

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PALABRAS CLAVE: agregados, reactividad alcali-silice, nivel alcalino del cemento, concreto, expansion, cenizavolante, pavimento, concreto reciclado

SINOPSIS: Se realizo una investigacidn acerca de las precauciones que son necesarias para evitar la expansion de lareactividad dcali-silice (RAS) en 10S concretos en 10S cuales se utiliza agregado grueso reciclado que previamente hasido afectado por dicha reaccion. Cementos con niveles de ~lcali de 0.50”/0,().750/.,y 1.OOOk,de NazO equivalence, seutilizaron con agregados gruesos y fines altamente reactivos para la fabrication de concretos que posteriormente fueronreciclados a edades de dos meses, y cuyas expansions se aproximaron a un medio de la maxima expansion y muy cercade la misma. Concretos nuevos fueron fabricados utilizando concreto recliclado como agregado grueso, agregados finesinnocuos, cementos con contenido alcalino de 0.500/.y 1.00%, y con o sin la utilization de ceniza volante. En todos 10Scases 10S ensayes se realizaron almacenando 10S especimenes dentro de recipients con agua sellados y mantenidos auna temperature de 38° C (100” F). Los resultados indicaron que expansions excesivas debidas a la RAS puedendesarrolarse en el concreto nuevo conteniendo concreto reciclado; particularmente, cuando cemento de bajo contenidoalcalino fue utilizado en el concreto original y cemento de alto contenido alcalino fue utilizado en el concreto nuevo.La substitution de cemento, en un 20% en masa, por ceniza volante ASTM-Clase F con bajo contenido de limo, redujola expansion a niveles adecuados de seguridad en el mayor numero de 10S cases. Observaciones de pavimentos deconcreto indicaron que la utilization de ceniza volante en el agregado de la mezcla de concreto, puede controlarexitosamente el potential de la RAS en aquellos concretos reciclados que previamente han sido afectados por dichareaccion.

REFERENCIA: Stark, David, The Llse of Recycled-Concrete Aggregate from Concrete Exhibiting Alkali-Silica Reactivity,Research and Development Bulletin RD1 14, Portland Cement Association, [El uso de agregado dc corzcreto recicladoproveniente de concreto que exhibe actividad hlcali-silice, Boletin de Investigaci6n y Desarrollo RD114, Asociaci6n deCemento Portland], Skokie, Illlinois, U.S. A., 1996.

STICH WORTER: Zuschlagstoff, Alkali-Kieselsaure-Reaktion, Alkaligehalt von Zement, Beton, Treiben, Flugasche,Gehweg, wiederverwerteter Beton

AU SZUG: Eine Untersuchung wurde durchgefi.ihrt, urn festzustellen, welche Vorsichtsmat3nahmen getroffen werdenmussen, urn die treibende Alkali-Kieselsaure-Reaktion (AKR) zu verhindern, wenn AKR-beinfluf?ter Beton als groberZuschlagsstoff bei neuem Beton wiederverwertet wird. Verwendet wurden Zemente mit Alkaligehalten von 0.50~0,t).75~0, und 1.OOO/.Na20 equivalent mit hochreaktiven feinen und groben Zuschlagsstoffen in wiederverwertetenUrsprungsbetonen, die im Alter von 2 Monaten und bei ca. 500/0maximalem Treiben und bei fast maximalem Treibenwiederverwendet wurden. Neue Betone mit wiederverwertetem Beton als groben Zuschlagstoff wurden mitnichtreaktivem feinen Zuschlagstoff und Zementen mit 0.50% oder 1.OOO1)Alkaligehalt sowie mit und ohne Flugaschehergestellt. Lagerung fur alle Falle war uber Wasser in geschlossenen Behaltern bei 38 ‘C. Die Ergebnisse zeigten, dat3iibermaf.?iges Treiben wegen AKR in den neuen Betonen mit dem wiederverwerteten Beton stattfinden kann, besonderswenn Zement mit niedrigem Alkaligehalt im Originalbeton und Zement mit hohem Alkaligehalt im neuen Betonbenutzt wird. ASTM Klasse F Flugasche mit niedrigem Kalziumgehalt als Ersatz ftir 20 Gew.-% Zement hat das Treibenfast immer auf ein sicheres Minimum reduziert. Beobachtungen an Betongehwegen deuten darauf bin, dafl AKRerfolgreich unter Kontrolle gebracht werden kann bei AKR-beinflut3tem Beton, der als Zuschlagstoff wiederverwertetwird, wenn Flugasche in der Zementmischung mitverwendet wird.

REFERENZ: Stark, David, The Use of Recycled-Concrete Aggregate from Concrete Exhibiting Alkai-Silica Reactivity,Research and Development Bulletin RD1 14, Portland Cement Association, [Gebrauch von wiederverwertetemBeton, der Alkali-Kieselsaure-Reaktion zeigt, als Zuschlagstoff Forschungs-und Entnicklungsbulletin RD114,Portlandzementverband], Skokie, Illinois, U.S. A., 1996.

PCA R&D Serial No. 2033

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