properties of ettringitic systems containing different calcium aluminates

1、PropertiesofettringiticsystemscontainingdifferentcalciumaluminatesBrunoTouzo1StephaneBerger2HerveFryda21.KerneosResearchCenterAsiaTianjinChina2.KerneosResearchCenterVaulxMilieuFranceAbstractCalciumaluminatecements(CAC)ar

2、ecommonlyusedinbuildingchemistryapplicationslikeselflevellingoverlaymentunderlaymenttileadhesivespecialmtars....Intheseapplicationsspecificpropertieslikerapidhardeningrapiddryingshrinkagecompensationaredeliveredthroughhy

3、drationofCACincombinationwithcalciumsulphatesleadingtorapidprecipitationofettringitealuminahydratespossiblyAFmhydratesinsomecases(monosulfomonocarboaluminates).HisticallythemainhydraulicphaseofCAChasbeenmonocalciumalumin

4、ateCaO.Al2O3CA.ThispaperinvestigatestheimpactofamineralogicalevolutionfromCAtoC12A7onearlyhydrationpropertiesincombinationwithcalciumsulphate.Hydrationkiicsismeasuredbymicrocalimetry.Solidliquidphaseevolutionareacterised

5、theirevolutionislinkedwithmacroscopicproperties.AlthoughCAC12A7globallyleadstothesamefamilyofhydratedcompounds(mainlyettringitealuminahydrate)imptantdifferencesareobservedinthekiicsofprecipitation.C12A7leadstoameefficien

6、thydrationoccurringinonestepwhereasitisusuallydividedintwostepswithCAasshownbymicrocalimetry.EarlyagepropertiesareenhancedinthecaseofC12A7:quickerhardeningdryingbettershrinkagecompensation.Globallythesystemappearstobemer

7、obusttochemistrytemperaturechanges.Thesedifferencesareinterpretedthroughamechanismbasedonsolubilityratestoichiometryofthepredominantcalciumaluminatephase.iginalityThiswksexplesanewmineralogyofcalciumaluminateswithasthema

8、inphaseC12A7tooptimizeettringitefmation.Keywds:calciumaluminateettringitehydrationkiicsselfleveler1Crespondingauth:bruno.touzo@Tel8622598383003.ResultsdiscussionTheSEMpicturesinBSEmodeshowinFigure1themicrostructureoftheC

9、12A7richcement.Thegeneralpictureontheleftatlowmagnificationshowthecementgrainswithatypicalmphologyofacrushedfusedclinker.Thegrainshaveaverylowposityedgesaresharpwelldefined.Thegrainsgenerallycontaindendriticstructurestyp

10、icalofaquenchedliquid.Sometimesthegrainshavelargercrystalsize.TheEDSanalyses(notshown)onthelargedarkareasshowsthattheseareasarecomposedofC12A7.ThisisthephasewhichshowsthehigherproptionasalsoconfirmedbytheXRDanalyses.Apar

11、tfromthelargeC12A7crystalsitisdifficulttodistinguishotherphases.Mineralswereveryfinelyintermixedasithappensfeutecticalcomposition.Howevertheseareasarebrightersuggestingahigheroverallheavyelementconcentration.Theseareassh

12、owhighironcontent.SomeTiO2alsoasmallamountofSiO2aremeasured.TheseareaslikelyconsistofintermixedcrystalofBrownmilleriteperovskitesilicate.WhenlookingcarefullyatthecompositiontheAl2O3Fe2O3molarratioisgreaterthan1.Thissugge

13、stthattheBrownmilleriteinthiscementhaveAl2O3Fe2O31whichisdifferenttostardgradeCACswherethisratioisusuallysmaller(PllmannH.2012).ThemicrostructureofthisC12A7richcementistherefemainlyacterisedbydendriticC12A7crystalsembedd

14、edinaeutecticmixmadeofthreemainphases.Medetailsonthemineralogycanbefoundintheliterature(TouzoB.2014).ThecalciumconcentrationduringthedissolutionoftheCACshasbeenmeasuredafter5minutes.Atthistimetheconcentrationofthediluted

15、suspensionhasstillnotreachedaplateau.Themeasuredcalciumconcentrationsare0.4mmollfCACCA1.2mmollfCACC12A7.ThissuggestsaquickerdissolutionofCACC12A7asitisabletodeliverfasterionstothesolution.Asthehydrationreactionofthesesys

16、temsoccursthroughdissolutionprecipitationreaction(ScrivenerK.L.1998)wecanexpectfasteroverallhydrationkiicsfthistypeofclinker.Figure1MicrostructureoftheCACC12A7cement.HardeningoftheSLUfmulationsshowsthatM1(OPC)M2areacteri

17、sedbyatwostepsprocessseparatedbyaninflectionpointontheultrasoundvelocitycurve(figure2a).SuchaninflectionpointisnotobservedfM3fwhichhardeningseemstooccurinonlyonestep.Calimetrycurves(figure2b)revealthesamedifferencebetwee

18、nthetwotypesoffmula:multistepprocessfM1(OPC)M2withseveralpeaksoveralongperiodonestepprocessfM3withasinglesharperpeak.Abalanceoftheheatofhydrationprecipitatedhydrateshasbeenevaluatedafter24hoursispresentedintable3.Fthethr

19、eefmulasthemainhydratedetectablebyXRDisettringite.Otherhydratephasesmaybepresentincludingaluminagelbuttheiroccurrenceisnotisnotstudiedinthispaper.ThefmulaswithCACCAhaveprecipitatedsimilaramountofettringitedisplaythesameh

20、eatofhydration.TheabsenceofOPCretardsthekiicsofhydrationbuthasnoimpactonthetotalheatreleasedat24h.TheresultsoftheCACC12A7hydrationaresignificantlydifferentshowhigherettringitecontentheatofhydration.Thisisnotlinkedtotheam