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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(