Silica Fu Me

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Behaviour of lightweight expanded polystyrene concretecontaining silica fumeK. Ganesh Babu*, D. Saradhi BabuStructures and Materials Laboratory, Department of Ocean Engineering, Indian Institute of Technology Madras, Chennai 600 036, IndiaReceived 17 January 2002; accepted 4 November 2002AbstractLightweight concrete can be produced by replacing the normal aggregate with lightweight aggregate, either partially or fully, dependingupon the requirements of density and strength. The present study covers the useof expanded polystyrene (EPS) beads as lightweightaggregate both in concretes and mortars containing silica fume as a supplementary cementitious material. The main aim of this project is tostudy the strength and the durability performance of EPS concretes. These mixeswere designed by using the efficiency of silica fume at thedifferent percentages. The resulting concretes were seen to have densities varying from 1500 to 2000 kg/m3, with the corresponding strengthsvarying from 10 to 21 MPa. The rate of strength gain for these concretes shows that an increase in the percentage of silica fume increases the7-day strength. This was observed to be about 75%, 85%, and 95% of the corresponding 28-day strength at the silica fume replacement levelsof 3%, 5%, and 9%, respectively. The results of absorption, at 30 min and the final absorption, show that the EPS mixes made with sand havelower levels of absorption compared to the mixes containing normal aggregates. F

urther, the absorption values were seen to be decreasingwith increasing cementitious content. The performance of these concretes, in terms of their chloride permeability and corrosion resistance,even at the minimal silica fume content level was observed to be very good.D 2002 Published by Elsevier Science Ltd.Keywords: Expanded polystyrene; Silica fume; Strength; Water absorption; Chloride permeability; Corrosion1. IntroductionThe demand for lightweight concrete in many applicationsof modern constriction is increasing, owing to theadvantage that lower density results in a significant benefitin terms of load-bearing elements of smaller cross sectionsand a corresponding reduction in the size of the foundation

[1]. Lightweight aggregates are broadly classified in to twotypesnatural (pumice, diatomite, volcanic cinders, etc.)and artificial (perlite, expanded shale, clay, slate, sinteredPFA, etc.). Expanded polystyrene (EPS) beads are a type ofartificial ultra-lightweight (density of less than 300 kg/m3),nonabsorbent aggregate [2,3]. It can be used to produce lowdensityconcretes required for building applications likecladding panels, curtain walls, composite flooring systems,and load-bearing concrete blocks [4,5]. Also, it was reportedthat it can be used for other specialized applications like thesub-base material for pavement and railway track bed; asconstruction material for floating marine structures, seabeds, and sea fences; as an energy-absorbing material for

the protection of buried military structures; and as fenders inoffshore oil platforms [610]. By incorporating the EPSbeads at different volume percentages in the concrete,mortar, or cement paste, a wide range of concrete densitiescan be achieved. The EPS aggregate replaces wholly orpartly the normal aggregate in the case of concrete, or sandin the case of mortars.Earlier researchers studied EPS mostly in mortar withOrdinary Portland Cement (OPC) as the binder. Also, toovercome its hydrophobic nature, bonding additives like


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water-emulsified epoxies and aqueous dispersions of polyvinylpropionate were added [11], or chemically treated EPSbeads which are capable of preventing the segregation in theconcrete mixes (commercially available as BST aggregate inAustralia) were used [12]. Other investigators also reportedthat EPS tends to float and can result in a poor mixdistribution and segregation, necessitating the use of admixtures[7,8]. Apart from this, most of the studies reported to0008-8846/02/$ see front matter D 2002 Published by Elsevier Science Ltd.doi:10.1016/S0008-8846(02)01055-4* Corresponding author. Tel.: +91-44-257-8623, +91-44-445-8623;fax: +91-44-235-0509.E-mail address: [email protected] (K.G. Babu).Cement and Concrete Research 33 (2003) 755762This document has beenedited with Infix PDF Editor- free for non-commercial use.To remove this notice, visit:www.iceni.com/unlock.htm


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K.G.Babu,D.S.Babu/CementandConcreteResearch33(2003)755762Table1Chemicalcompositionofcementandsilicafume

ChemicalcompositionCementSilicafumeSilica(SiO2)21.7874.07Alumina(Al2O3)6.562.22

Ferricoxide(Fe2O3)4.131.57Calciumoxide(CaO)60.122.95Magnesiumoxide(MgO)

2.081.27Sodiumoxide(Na2O)0.362.89Potassiumoxide(K2O)


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0.426.51Sulphuricanhydride(SO3)2.160.95Lossonignition(LOI)2.397.67

datewereessentiallyonconcretesoflowerdensities(below

1300kg/m3)resultinginstrengthsbelow12MPa.

Thepresentstudy

isanefforttodevelopstructurallightweightconcretesof14401850kg/m3withthe

correspondingstrengthsofabout17MPaminimum[1].Concretescontaining


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silicafumeasthesupplementarycementitiousmaterialwithnormalcoarseaggregateandEPS,withoutaddinganybondingadditiveswereinvestigated.Also,itiswellunderstoodthat

forconcretestoqualifyasstructuralmaterials,itisimportantthatapartfrom

thestrength,durabilityandcorrosionresistanceparametersneedaspecificassessment.Inview

ofthis,theinvestigationsincludedbothparametersrelatedtostrength


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likecompressiveandsplittensilestrengths,andthedurabilityparameterslikewaterabsorption,chloridepermeability,corrosionrate,andacceleratedcorrosioncracking.

2.

Mixproportions2.1.MaterialsCementconformingtoIS:12269(C53grade),whichwillalso

confirmtoASTMTypeI,andsilicafumewereusedas

Table2DetailsofEPSconcretemixescontainingsilicafume


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cementitiousmaterialsintheconcretemixes.ThechemicalcharacteristicsofthecementandsilicafumearegiveninTable1.SeriesI

andIIIcontainsandfinerthan2.36mm,whileSeriesIIcontainssand

finerthan1.18mm.Themaximumsizeofthenormalcoarseaggregate(crushed

bluegranite)inSeriesIandIIwas10mm,


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whileitwas16mmforMixes8and10and20mmforMixes9and11.Inthepresentstudy,Mixes10

and11weredesignedwiththesametotalcementitiousmaterialandw/(c+

s)ratio,aswasreportedearlierbyZhangandGjorv[13]forlightweight

concretescontainingexpandedclay-typeaggregates.Twotypesofcommerciallyavailable


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sphericalEPSbeadsthatareessentiallysinglesized(TypesAandB)wereused.ThegradingshowsthatTypeAhasmostly6.3-mm-sizebeads

andTypeBhasmostly4.75-mm-sizebeads.Thebulkdensityandthespecific

gravityofthesebeadswere9.5kg/m3and0.014forTypeAand

20kg/m3and0.029forTypeB,respectively.Anaphthalene-based


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superplasticizerwasusedtoproducethemixesofflowableorhighlyflexiblenaturetosuitthehandcompactionadopted.

Thedesignof

EPSmixeswithsilicafumewasbasedontheefficiencyconceptsuggestedearlier

[14].Threepercentagesofsilicafume3%,5%,and9%(byweightofthe

totalcementitiousmaterials),withthecorrespondingefficiencyvaluesof7.5,


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5.0,and3.5wereused.Themixeswerealldesignedasconcretesconsideringtheefficiencyofsilicafume.Thereductioninthecementpastephase

resultingfromthehighefficiencyofsilicafumewascompensatedtoacertain

degreebyadditionalfines.Thecompletedetailsoftheconcretemixesarepresented

inTable2.

2.2.ProductionofEPSconcrete


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Concretewasmixedinaplanetarymixerof100-lcapacity.EPSbeadswerewettedinitiallywithapartof

SlMixCement

SF(s)Waterw/(c+s)TotalSandaNormalCAasEPSc%

VolumeSP%Flownumbernumber(kg/m3)(%)(kg/m3)ratioaggregates(kg/m3)(kg/m3)

aggregatesb(kg/m3)TypeA(kg/m3)TypeB(kg/m3)ofEPS


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ofTCM(mm)SeriesI135031580.440175248132572522136.40.2547236231640.4401724

48848157917629.00.2548337531700.4401691

49764842012621.00.2547433531520.4401786

77989411334.40.5048SeriesII5


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39951850.440160649853057822.20.552639951850.4401606102857822.20.5

55739951850.440160674386333.20.5

49SeriesIII839951850.4401606337515321433

28.70.2551939951850.4401606337


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51532143328.70.5531060591850.278145430546629139226.30.5581160591850.278

145430546629139226.00.7555

CAnormalcoarseaggregate;

SFsilicafume.

aThesizeofsandusedinSeriesII

was1mm,downgraded;andinSeriesIandIII,


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thesizeswere2.36mm,downgraded.

bA10-mmdowngradedaggregatewasusedinSeriesIandII,16mmdowngradedin

Mixes8and10,and20mmdowngradedinMixes9and11.

TheweightofCAisconvertedtoanequivalentvolumeof

EPS(thebulkdensityofCA,EPSTypeA,and


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TypeBwere1600,9.5,and20kg/m3respectively).


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K.G.Babu,D.S.Babu/CementandConcreteResearch33(2003)755762themixingwaterandsuperplasticizerbeforeaddingtheremainingmaterials.Mixing

wascontinueduntilauniformandflowingmixturewasobtained.Thefreshconcrete

densitiesandflowvaluesweremeasuredimmediatelyafterthemixing.Theflowvalues

variedbetween47and58cmandfacilitatedhandcompaction.


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Thespecimenswerecuredunderwetgunnybagsinitiallyand,afterdemolding,werestoredinwater.

3.Experimentalinvestigations3.1.Specimensand

curingconditionsStandardtestspecimensofdifferentsizeswerechosenforinvestigatingthe

variousparameters.Cubesof100mmsizewereusedforstudyingthecompressive

strengthsat1,3,7,28,and90daysand


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alsofortheabsorptiontestsat90days.Splittensilestrengthtestwasconductedon100mmdiameter.200mmcylindersat28

days.Cylindersof50mmthicknessand100mmdiameterwereusedfor

thechloridepermeabilitystudiesat90days.Cylindersof100mmdiameter.

200mmwithan8-mm-diameter,hot-rolled,deformedsteelbarof


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100mmofexposedlengthembeddedinthemiddlewereusedtostudythecorrosionrateandacceleratedcorrosioncracking.Thesespecimensalonewerecured

inseawateruntiltesting(90days)after3daysofnormalwatercuring.

3.2.TestprogramTheflowvaluesofthefreshconcretemixes

weremeasuredaccordingtoASTMC124-1973.Compressivestrengthtest


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wascarriedoutinatestingmachineof2000kNcapacityataloadingrateof2.5kN/s.Thesplittensilestrengthtestwas

conductedoncylindersat28daysasperASTMC496-89.Theabsorption

testwascarriedoutasperASTMC642-82.Saturatedsurfacedrycubes

werekeptinahotairovenat60C


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(althoughASTMsuggestsatemperaturerangeof100110C)untilaconstantweightwasattained.Thisisbecauseatthistemperaturerangeof100

110C,theEPSbeadsinitiallyshrinkandfinallyevaporate.Thesearethen

immersedinwaterandtheweightgainismeasuredatregularintervalsuntil

aconstantweightisreached.Theabsorptionat30min


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andthefinalabsorption(atapointwhenthedifferencebetweentwoconsecutiveweightsat12-hintervalwasalmostnegligible)werereportedtoassess

theconcretequality.

Thestudiesforthedurabilityrequirementswereundertaken

onlyontheconcretesofSeriesI,asthesecontainedtheleastamount

ofsilicafumethatimprovedtheperformancesignificantly(highestefficiency


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andacorrespondinglylowercementitiousmaterialscontent)andpresentedthelowestdurabilitythatcanbeexpected.Thesewerelimitedtochloridepermeability,potential,corrosion

rate,andacceleratedcorrosionstudies.

Thechloridepermeabilitytestwasconducted

toassesstheconcretequalityasperASTMC1202-94.Apotentialdifference

of60VDCwasmaintainedacrossthespecimen.One


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ofthesurfaceswasimmersedinasodiumchloride(NaCl)solutionandtheotherinasodiumhydroxide(NaOH)solution.Thetotalchargepassing

in6hwasmeasured,indicatingtheresistanceofthespecimentochloride

ionpenetration.

Potentiodynamicpolarizationtechniquewasadoptedtomeasurethecorrosion

rateofthe8-mm-diameterbarsinthecylinderspecimens,by


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usingascanningpotentiostat(EGandGPAR-Model362)andanXlogX,Yrecorder.Apotentialof250mVwasappliedoneither

sideoftheopencircuitpotential(OCP),andthecorrosioncurrent(Icorr)was

takenat100mVfromthepotentiodynamicplot.Thecorrosionratewascalculated

fromIcorrbyusingFaradaysequation.

Acceleratedcorrosion


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dailyresistancewascalculated.Later,toacceleratethecorrosionprocess,acurrentof60Vwasappliedforaperiodof10daysor

untilacrackoccurred.Thecurrentpassingwasmeasuredatregularintervalsto

evaluatethechargetocracking.

4.ResultsanddiscussionsAcomprehensive

summaryofthedifferentstrengthsandabsorptioncharacteristicsofall


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theconcretesispresentedinTable3.Theresultsofthecorrosion-relatedparametersinvestigatedforSeriesI,asalreadyproposed,aregiveninTable

4.

4.1.FreshconcreteTheworkabilityoftheconcreteinterms

oftheflowmeasurementswasreportedinTable2.Flowvaluesofthe

allthemixeswereintherangeof4758cm.


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Theseflowvaluescorrespondtoaslumpofabout5070mminmostcases.Themixeshavingthehigherpercentagesilicafumeshowhigher

flowvalues.Alltheconcreteswereflexibleandeasytoworkwith,and

couldbeeasilycompactedusingjusthandcompactionandcouldalsobeeasily

finished.Theproblemsassociatedwiththesegregationandfinishabilityof


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themixescontainingcoarsebeadsasreportedearlier[7]weretotallysolvedbyensuringthataminimumamountofcementitiousmaterialwasalwayspresent.

Thesilicafumeandthesuperplasticizerwereessentiallyaddedtohelpsolvethe

problemsassociatedwiththehydrophobicnatureoftheEPSbeadsandtoimprove

thecohesivenessofthemix.


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K.G.Babu,D.S.Babu/CementandConcreteResearch33(2003)755762Table3StrengthandabsorptionofEPSconcretemixes

SlMixFreshconcreteCompressivestrength(MPa)SplittensileAbsorption(%)numbernumber

density(kg/m3)1day3days7days28days90daysstrength

(MPa)30minFinalSeriesI115524.26.6


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7.610.210.61.530.6955.424216985.87.211.215.014.02.040.9035.3553197910.212.814.021.421.22.16

1.0494.882415034.46.88.410.212.22.100.7414.596Series

II518565.210.615.219.819.12.231.3063.52061748

5.010.417.618.518.62.201.2443.14071546


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4.09.212.415.014.92.150.7302.570SeriesIII817626.610.211.612.011.21.831.3503.630917714.69.8

14.21717.22.021.2503.1501017939.813.415.616.216.5

2.221.2702.5401118739.816.419.820.821.22.321.0002.340

4.2.Compressivestrength4.2.1.EffectofageThe


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variationofthecompressivestrengthwithageshowsacontinuousincreaseinalmostallthemixes.Therateofstrengthdevelopmentwasgreaterinitially

anddecreasedastheageincreased.Therateofstrengthgainat7,

28,and90daysispresentedinFig.1.Acomparisonofstrengths

at7daysrevealsthatconcreteswith3%silicafume


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developedalmost75%ofits28-daystrength,whilethatwith5%and9%silicafumedevelopedalmost85%and95%ofthecorresponding28-day

strength.Therewasnoappreciablestrengthimprovementat90days.Fromthis,it

isclearthattherateofstrengthgainwasincreasingwithanincreasing

percentageofsilicafume.

4.2.2.Effectofdensity


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andEPSvolumeThedensityoftheconcretewascontrolledbyvaryingtheEPSvolumeinthemix.Thevariationofcompressivestrengthwith

theplasticdensityofconcrete(andpercentvolumeofEPS)waspresentedin

Fig.2.ThestrengthofEPSconcretesappearstoincreaselinearlywithan

increaseinconcretedensity,orwithadecreaseinthe


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EPSvolume.

4.2.3.EffectofEPSbeadsizeThestrengthofEPSconcreteincreasedwithadecreaseintheEPSbeadsize

forthesamemixproportions.Thisis

Table4Corrosionstudies

onEPSconcretes(SeriesI)

SlnumberCharge(C)90-dayOCP

(.mV)Corrosionrateat100mV(mpy)ACCstudies


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ADR(V)Totalchargetocracking(C)Mix1Mix2Mix3Mix4676.74496.37460.71372.513303006703050.502

0.3900.4510.3645.405.605.304.1017,94220,97412,66913,176

ACCacceleratedcorrosioncracking;ADRaveragedailyresistance.

clearfromtheresultsof

theconcretesofSeriesIImadewithonlyTypeB


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(smallerEPSbeads),whichshowedhigherstrengthvalues,thanthemixesmadewiththecombinationofTypeAandTypeBbeadsforthe

sameconcretedensities.

4.2.4.EffectofnormalaggregatesizeComparingthe

strengthresultsofMixes8and10containing16-mm,downgraded,normalcoarseaggregate

withthoseofMixes9and11containing20-mm,downgraded,


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normalcoarseaggregate(Fig.3),itisclearthatthecompressivestrengthincreasedwithincreasingaggregatesize.Thepercentageincreaseinstrengthwithsize

wasalsoobservedtobehigherintheleanmixescomparedtothe

richmixes.

4.2.5.EffectofsandMixes1and5contain

bothsandandcoarseaggregatewhilecorrespondingMixes4and


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6containonlysandastheaggregate(mortar).Themixproportionsofthetwomixsets(Mixes1and4,andMixes5and

6)arealsonearlythesame.Acomparisonofthestrengthresultsof

thesetwosetsofmixeshavingcomparabledensitiesclearlyshowsthattheeffect

ofsandisnegligible,bothintermsofthestrength


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gainrateaswellasthestrengthat90days.However,itwasobservedthatthemixescontainingcoarseaggregatesalwaysshowaslight

increaseindensity(about50100kg/m3).

4.2.6.Effectoflightweightaggregate

strengthThestrengthofconcreteismainlyinfluencedbythestrengthofthe

aggregate.Thedevelopmentofhigh-strengthconcretesispossibleonlywhen


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theaggregateshaveenoughstrength.Presently,Mixes10and11weredesignedwiththesametotalcementitiousmaterialandw/(c+s)ratioas

werereportedearlierbyZhangandGjorv[13].Theyreporteda28-daycompressive

strengthof102.4MPafortheseconcretesmadewithexpandedclayaggregate.However,

the28-daystrengthforMixes10and11containingEPS


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wereonly16.2and20.8MPa,respectively,inthepresentstudy.


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K.G.Babu,D.S.Babu/CementandConcreteResearch33(2003)755762Fig.1.Variationofcompressivestrengthwithage.

This

widevariationofstrengthismainlyduetothedifferenceinstrengthof

theaggregates,asEPSaggregateshavealmostzerostrength.

Moreover,the

failuremodeoftheconcretespecimenscontainingEPSaggregatesunder


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compressiveloadingdidnotexhibitthetypicalbrittlefailurenormallyassociatedwiththeconventionalaggregateconcrete.Thefailureobservedwastobemoregradual

(morecompressible),andthespecimenswerecapableofretainingtheloadafterfailure

withoutfulldisintegration.Asimilartypeoffailurewasalsoreportedearlierfor

plasticshreddedaggregateconcretes[16].Thisclearlyshowsthehigh


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energyabsorp

tioncapacityoftheseconcretesthatwassuggestedearlier[5,9].

4.3.SplittensilestrengthThevariationoftensile

strengthwiththecompressivestrengthisgiveninFig.4.Fromthis,it

canbeseenthatthetensilestrengthincreasedwithanincreaseincompressive

strength.Thesplittingfailuremodeoftheconcretespecimenscontaining


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EPSaggregatesalsodidnotexhibitthetypicalbrittlefailurenormallyobservedinconventionalconcreteasincompressivestrength.Thefailureobserved

Fig.2.VariationofstrengthwithdensityandEPSvolume.


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K.G.Babu,D.S.Babu/CementandConcreteResearch33(2003)755762Fig.3.Variationofcompressivestrengthwithage(SeriesIII).

wasmoregradual(compressible)andthespecimensdidnotseparateintwo,

aswasearlierreportedforplasticshreddedaggregateconcretes[16].

4.4.

AbsorptionThedurabilityofconcreteprimarilydependsuponitspermeability,


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whichdefinestheresistancetotheingressofaggressiveions.Theabsorptioncharacteristicsindirectlyrepresenttheporosity,throughanunderstandingofthepermeablepore

volumeanditsconnectivity.Alimitontheinitial(30min)absorptionfor

assessingtheconcrete

qualitywasdefinedbyCEBearlier[17].The

initialabsorptionat30min,aswellasthefinal


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(total)absorption,wereshowninFig.5.AspertheassessmentcriteriagivenbyCEB,allthemixesinthepresentstudyshoweda

lowabsorptionrating(

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