fsn_ 930 - nicoleau luc - 2. hydration of pc - full paper

1、TheC3SdissolutionadeterminingkiicfactduringhydrationLucNicoleau1BASFConstructionMaterials&SystemsResearchTrostbergGermanyAbstractTricalciumsilicate(C3S)isacompoundwhichreactswithwatertogivehydrationproducts(CSHCH).Thetra

2、nsfmationi.e.thehydrationoccursbysimultaneousdissolutionprecipitationreactions.Thedifferentfactsinfluencingthehydrationarethereactivesurfaceareasi.e.thegrowthsurfaceofCSHthedissolutionsurfaceofC3Sthecompositionofthepesol

3、ution.WhenonlypureC3Sismixedwithwaterthesolutioncontainsonlycalciumhydroxidesilicateions.ThethreespeciesaretheconstituentsofC3SCSH.Theydeterminebothinterfacialreactionrates:theC3Sdissolutionratethroughtheundersaturationw

4、ithrespecttotheC3SsolubilitytheCSHprecipitationratethroughthesupersaturationwithrespecttotheCSHsolubility.Sofarallcementhydrationtheiesreptedintheliteratureconsideredtheincreaseoftheprecipitationsurfaceareaastheonlycause

5、oftheaccelerationofhydration.AlsothehydrationpeakasobtainedbyisothermalcalimetrytheinherentdeceleratingperiodhavebeenrationalizedbytheiesexclusivelybasedonCSHgrowthimpingement[Thomasetal.2011].Howeveraseriesofexperiments

6、demonstratesthatthesetheiescannothold.Converselythereisabodyofexperimentaltheeticalevidencesthatthedissolutionrateisthekiicdriverduringthefirsthoursofcementhydration.Experimentalobservationsalsoindicateanincreaseofthedis

7、solutionsurfacearearecentNMRexperiments[d’Espinoseetal2014]showthatthesurfaceareaofC3Sincontactwithwaterdecreasesalmostatthesametimeasthemaincalimetrichydrationpeak.Atopographicalmodelbasedonthefmationofetchpitstheetical

8、lysupptstheseexperimentalfindingslaidakiicgroundwkfexplingthekiicconsequencesonthehydrationrate.Thefirstoutcomesare(1)thepossibilitytoinferadmantlikeperiodwithonlyafewassumptions(2)thedevelopmentofthereactivedissolvingsu

9、rfaceareapassingthroughamaximum.iginalityThisstudypresentstheroleofthedissolutionsurfaceareaitsevolutionduringC3Shydration.InadditionanovelviewonthelimitationofC3Shydrationkiicsbasedonthedissolutionisproposed.Thisproposi

10、tionisuniqueintheliteraturesofar.Keywds:Hydrationkiicsgrowthmodeldissolutionmodelaccelerationpeakinductionperiod.1Crespondingauth:luc.nicoleau@Tel498621862734Fax49862186502734inthefollowing.Thefirstoneproposesthecoalesce

11、nceofCSHplateletsontoonerepresentativeC3SgrainthesecondonesuggeststhemergingoflowdenseCSHlayersgrowingfromdifferentC3Sgrains(seeschemesinfig.7).Yetsomeexperimentalobservationsstronglychallengebothmodels.Sincethehydration

12、kiicsisfairlyindependentofthedilutionofthesystem[Daot1994]itcallsintoquestiontheassumptionsofBishnoi’smodel.SecondlysystemsacceleratedbyCSHnuclei[Nicoleau2013b]showingC3Ssurfacescompletelydevoidofhydrationproductsattheea

13、rlyageofhydration[Nicoleau2015]alsorevealsimilarshapesofthecalimetrichydrationcurveswhichinturntendstoinvalidatetheGarrault’shypothesis.MotivatedbythesenotcompletelysatisfyingCSHgrowthbasedtheiestheC3Sdissolutionmeexactl

14、ytheevolutionoftheC3Sreactivesurfaceareahasbeenexperimentallystudiedmodelled.Somefeaturesofthisnewmodelareexpectedtoexplainthestillopenquestionsrelatedtohydrationkiicsmentionedabove.2.Results–EvolutionoftheC3Sdissolution

15、surfaceareaattheearlyageInthissectionabodyofexperimentscarriedoutatourlabsdrawnontheliteraturehasbeencompiledindertoshedalightonthedevelopmentoftheC3Ssurfaceareaduringitsdissolution.2.1.Calculationofthereactivesurfaceare

16、afromhydrationratespesolutioncompositions.Firstevidencecomesfromtheevolutionoftheundersaturationduringtheearlyhydration.AstheundersaturationtheC3Sinterfacialdissolutionratearemathematicallylinkedbyamonotonousfunctiontheu

17、ndersaturationevolutionrevealsanyvariationoftheinterfacialdissolutionrate.Anempiricallawhasbeenrecentlyproposedin[Nicoleau2013].AlthoughthislawdoesnottakeintoaccountsomesecondderparametersaffectingtheC3Ssurfacesolubility

18、(aspHotherionspecificeffects)itenablesanestimationoftheinterfacialdissolutionrateRiC3S(?G)asafunctionofthecompositionofthesolution.Meoverthementionedsecondderparametersdonotsignificantlyvaryduringthemainhydrationpeakthus

19、theevolutionoftheinterfacialdissolutionratecanbeconsideredasfairlyaccurate.InFig.2twoexperimentsfromtheliteraturearerepted.Theionconcentrationsallowedusthecalculationofln?C3S.Bothexperimentsexhibitthehydrationpeakshowing

20、amaximumacoupleofhoursafterthebeginningofthereaction.Untilthismaximumthehydrationacceleratesbuttheundersaturationremainsquasiconstant.ItturnsoutthatRiC3Sdoesnotnotablyincrease.AsEq.2indicatesifthehydrationaccelerationi.e

21、.thedissolutionaccelerationdoesnotcomefromahigherundersaturationthenithastocomefromanincreaseofthedissolutionsurfacearea.Fig.2highlightstherelativeevolutionofthedissolutionsurfacearea(SC3S(t)SC3S(t=0)withSC3S=RhydRiC3S).

22、Theevolutionofthehydrationrate(Fig.2)theevolutionofthedissolutionsurfacearea(Fig.3)goclearlyhinhi.e.theirrespectivemaximumoccursatthesametime.Figure2(A)Evolutionof(1)thedegreeofhydrationofalite(D.O.H.)byQXRDduringthehydr

23、ationat20Cofandinaryptlcementmixedatawatertocementratioof0.5(2)thecrespondinghydrationrate(3)theionactivityproductcalculatedfromtheconcentrationsreptedbyLothenbach&al.in[Lothenbach2006].(B)Evolutionofthesamevariablesduri