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1、AcceleratingeffectofsaltsonC3SHydrationNonatA1BegarinF1PlusquellecG1GauffiS1NicoleauL21.ICBUniversityofBourgogne21078DijonFrance2.BASFConstructionSolutionsGmbH83308TrostbergGermanyAbstractThewellknownacceleratingeffectof

2、mineralsaltsonthehydrationofalitethemaincomponentofptlcementisrevisitedinthiswk.Theobjectiveofthisstudyistoidentifythemechanismsleadingtotheaccelerationofhydrationtheiginoftheionspecificity.Theeffectsoffourcalciumsaltsca

3、lciumchlidebroeiodidenitrateoffouralkalisaltssodiumpotassiumchlidesnitratesareinvestigatedoveraconcentrationrangeof0.1to0.5molofanionL.Theroleofsaltsontheinitialhydrationperiod(initialdissolutionofalitenucleationofCSH)on

4、thesocalledacceleratydeceleratyhydrationperiodsisseparatelystudied.DuringtheCSHnucleationsteptheamountofCSHisquantifiedbysolutionanalysisindilutesuspensions.TheaccelerationofhydrationisevaluatedbyisothermalcalimetryonC3S

5、samplesprehydratedinsaltfreesolutiontosettheamountofCSHnuclei.ThenthedegreeofhydrationcurvesaresimulatedwithanaggregationgrowthbasedmodelbuiltusingfourparametersdescribingthegrowthofCSHonthesurfaceofalite.Theyarethenumbe

6、roffirstgrowthsitesi.e.thenucleitheparallelperpendicularaggregationratesthepermeabilitycoefficientofCSH.BesidethekiicstudytheinteractionsbetweenCSHthesaltsolutionsarestudiedatequilibriumbyacoustophesiswithionspecificelec

7、trodes(pHCaClBr).ItturnsoutthatregardlessoftheaniontheamountofCSHprecipitatedduringthefirstminutesofhydrationsignificantlyincreaseswiththecalciumsaltconcentrationwhereastheadditionofalkalisaltsshowsasmalleffect.Onthecont

8、rarythehydrationratesignificantlyvarieswiththetypeofanionincreaseswiththeconcentrationofsalt.AccdingtoparametersfittedwithintheCSHaggregationbasedmodelthisaccelerationcanbeinterpretedasanincreaseoftheperpendicularCSHaggr

9、egationrateassociatedwithanincreaseofthepermeabilitycoefficientofCSH.HoweverthestudyoftheinteractionsattheinterfacebetweenCSHthesaltsolutionsdoesnotrevealanyadsptionofanionsontoCSHafeaturewhichcouldbeexpectedtobeattheigi

10、nofamodificationofCSHgrowththusanaccelerationofhydration.OnthecontraryionspecificeffectsarerevealedinsolutionleadingtoatleastthedecreaseoftheactivityofOHions.Theconsequencecouldbeanincreaseoftheundersaturationwithrespect

11、toC3S.Itwouldincreasethedissolutionratethatcouldbetheiginoftheaccelerationofhydration.iginalityTheiginalityofthiswkonanalreadylargelystudiedtopicliesinthefollowingpoints:Decouplingoftheeffectofsaltsonthedifferentstagesof

12、hydrationSimulationoftheexperimentalkiicscurveswithamodelbasedonphysicallysignificantparameterstoidentifyquantifytheeffectsStudyofthesolutionchemistryinteractionbetweentheCSHsurfaceionsKeywds:HydrationC3Skiicsacceleratsm

13、odeling1Crespondingauth:Tel333803961662.2.ExperimentalMethodsEffectofsaltsontheveryearlyhydration.HydrationsofC3SinstirreddilutesuspensionshavebeenperfmedindertoestimatetheeffectofsaltsontheCSHnucleationthroughthedetermi

14、nationoftheamountofCSHprecipitatedduringthefirst30minutes.1gofC3Swasstirredin100mLoflimesolution([Ca(OH)2]=11mM)withdifferentsaltconcentrationrangingfrom0to500mM.Thelimeconcentrationhasbeenchosenindertohaveasignificantam

15、ountofCSHwithouthydratingsignificantlyC3Sasitwouldbeinwater(seefexample(Garrault2001)fdetails).Asmallptionofsuspensionwascollectedfiltered(0.3mMillipefilter)afterseveralhydrationtimes:03060901201501803009001800seconds.Th

16、econcentrationsofCaSiNaKateachsamplingtimeweremeasuredbyICPOpticalspectrometry(VistaProVarian).nCSHtheamountofCSHprecipitatedduringthisperiodoftimewascalculatedaccdingtotheequationnCSH=V?(?[Si]?(13?(CS)–1)1?[Ca]?(3(CS))1

17、)(GarraultNonat2001)whereVisthevolumeofsolution?[Si]?[Ca]thevariationofSiCaconcentrationsmeasuredduringtheconsideredperiodoftimeCSthecalciumtosiliconratioofCSH.Alltheexperimentswerereplicatedthreetimes.Effectofsaltsonthe

18、acceleratydeceleratyperiodsofC3Shydration.IndertodecoupletheeffectofsaltsontheCSHnucleationfromtheeffectontheCSHgrowthprehydratedsamplesacterizedbyaconstantamountofCSHnucleihavebeensynthesizedfurtherhydratedindifferentsa

19、ltsolutions.Theprehydrationstepwasperfmedasdescribedabovebutinsaltfreeconditions.After30minutesof(pre)hydrationthesuspensionwasfilteredthesolidwasrinsedwitha11ethanolwatermixturethenwithpureethanoldriedundervacuumovernig

20、ht.Theprehydratedsampleswerefurtherhydratedinasolutionsaturatedwithrespecttoptlitecontainingdifferentsaltconcentrationsrangingfrom0to500mM.Theliquidtosolidweightratiowas0.5themixturewasmechanicallystirredf2minutesinaplas

21、ticampoule.Theampoulewasthenintroducedinanisothermalcalimeter(25CTAMAirThermometrics)theheatflowwasrecdedf1day.Eachexperimentwasreplicatedtwice.ThedegreeofC3Shydrationwascalculatedbyintegratingtheheatflowovertimeconsider

22、ingtheheatofhydrationofC3Sequalto105kJmole(Grant2006).TheexperimentaldegreeofhydrationcurveswerefittedusingahydrationmodelbasedontheanisotropicaggregationgrowthofCSHontothesurfaceofC3Sgrains(Garraultetal2001Garraultetal2

23、005Garraultetal2006)assuminganisotropicdissolutionofthoseC3Sgrains(Garraultetal2010).ThegrainsizedistributionofC3Sisdescribedby5monomodalpopulationseachgrainissupposedtohydratewithoutanyinteractionwiththeothergrains.TheC

24、SHgrowthisdescribedbyfourparametersthatarethenumberofinitialnucleithegrowthratesparallelperpendiculartotheC3SsurfacethepermeabilityofCSH.Intheexperimentsaswellasinthesimulationsthenumberofnucleiisfixedremainsconstantbeca

25、useoftheprehydrationstep.InteractionofsaltswithCSHTheinteractionsofCaCl2CaBr2Ca(NO3)2withthesurfaceofCSHhavebeenstudiedinsituindiluteCSHsuspensionsbymeansofseveralprobesthatareconductivitypHCaClBrspecificelectrodes(ISE)o

26、peratingsimultaneouslywithaTitrodevice(Metrohm).Thesignalofthoseprobeswasrecdedduringtheadditionof8mLofaconcentratedsolutionofsalt([CaCl2]=5.43M[CaBr2]=4.48M[Ca(NO3)2]=3.39M)in20stepswithanautomaticburette(DosinoMetrohm)

27、into250mLofCSHsuspension(ls=20).Anewadditionofsolutionisdonewhentheelectrodesignalsbecamestable.ReferenceexperimentswereperfmedoncalciumhydroxidesolutionsofthesameconcentrationastheCSHsuspensions(respectively4mM20mM)inde

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