2019Four-Dimensional-X-ray-Microtomography-Study.p

DaleBentz,PhillipHalleck,AbrahamGrader,andJohnRobertsRILEMConference-VolumeChangesofHardeningConcrete:TestingandMitigationAugust2006Outline•Needforinternalcuring–Blendedcements•“Undercuring”withinternalcuring•Microtomographyobservationsofwatermovementduringinternalcuring–Quantitativeanalysisof3-Dimages•MixtureproportioningforinternalcuringWhatisinternalcuring(IC)?Answer:AsbeingconsideredbyACI-308,“internalcuringreferstotheprocessbywhichthehydrationofcementoccursbecauseoftheavailabilityofadditionalinternalwaterthatisnotpartofthemixingwater.”Formanyyears,wehavebeencuringconcretefromtheoutsidein,internalcuringisforcuringfromtheinsideout.Internalwaterisgenerallysuppliedviainternalreservoirs,suchassaturatedlightweightfineaggregates,superabsorbentpolymers,orsaturatedwoodfibers.:ParticularlyinHPC,itisnoteasilypossibletoprovidecuringwaterfromthetopsurface(forexample)attheratethatisrequiredtosatisfytheongoingchemicalshrinkage,duetotheextremelylowpermeabilitiesthatareoftenachievedintheconcreteasthecapillaryporesdepercolate.Capillaryporepercolation/depercolationfirstnotedbyPowers,CopelandandMann(PCA-1959).HowdoesICwork?Answer:ICdistributestheextracuringwater(uniformly)throughouttheentire3-Dconcretemicrostructuresothatitismorereadilyavailabletomaintainsaturationofthecementpasteduringhydration,avoidingself-desiccation(inthepaste)andreducingautogenousshrinkage.Becausetheautogenousstressesareinverselyproportionaltothediameteroftheporesbeingemptied,forICtodoitsjob,theindividualporesintheinternalreservoirsshouldbemuchlargerthanthetypicalsizesofthecapillarypores(micrometers)inhydratingcementpasteandshouldalsobewellconnected(percolated).CementpasteWaterreservoirBlendedCements•Internalcuringcanbeparticularlyimportantinhigh-performance(loww/cm)blendedcementsystems–Increasedchemicalshrinkageofpozzolanicandslagreactions•Cement:0.06to0.07mL/gcement•Silicafume:0.22mL/gcement•Slag:~0.18mL/gcement•Flyash(TypeF):~0.12to0.16mL/gcement–PossibleearlierdepercolationofcapillaryporesandreducedpermeabilitylimitingwatertransportdistanceswithinthehydratingblendedcementpastemicrostructureAutogenousDeformationResultsICaddedviafineLWAtoincreasetotal“w/c”from0.30to0.38or0.40Note–chemicalshrinkageofpozzolanicreactionofsilicafumewithCHis~0.22gwater/gsilicafumeorabout3.2timesthatofcementw/c=0.3HPMsilicafumeblendedcement-500-400-300-200-10001002000714212835424956Time(d)MicrostrainControlIC-8IC-10AutogenousDeformationResultsICaddedviafineLWAtoincreasetotal“w/c”from0.30to0.38Note–chemicalshrinkageofslaghydraulicreactionsis~0.18gwater/gslagorabout2.6timesthatofcementw/c=0.3HPMslagblendedcement-600-500-400-300-200-10001000714212835424956Time(d)MicrostrainControlIC“Undercuring”withInternalCuring•Hydratingcementpasteisacomplexanddynamicporousmediaandassuch,internalcuringmixtureproportionsthatsupplyonlypartofthetotalneededwater(demand)canpotentiallyexhibitsomeinterestingresultsasillustratedintheschematiconthefollowingslideEmptyandFullPoresSaturatedcuringSealedcuringRH=98%RH=93%SufficientInternalcuringICReservoirCementpasteRH=97%InsufficientInternalcuringCementpasteRH=90%ICReservoirBetterhydrationOnlyporesinreservoirsemptySomeincreaseinhydrationPoresinbothreservoirsandpasteemptyCementpasteCementpasteLesshydrationLargestporesinpasteemptyFour-DimensionalX-rayMicrotomography•X-raymicrotomographyallowsdirectobservationofthe3-Dmicrostructureofcement-basedmaterials–Example:VisibleCementDataSet•InOctober2005,experimentswereconductedatPennsylvaniaStateUniversitytomonitorthree-dimensionalwatermovementduringinternalcuringofahigh-performancemortaroverthecourseoftwodays(timeisthe4thdimension)MixtureProportionsTable1.MixtureproportionsforthecontrolandIChigh-performancemortars.MaterialControlMortarMassICMortarMassCement984.6g(2.17lb)953.3g(2.10lb)Water344.6g(0.759lb)333.7g(0.735lb)Sand(total)1870.8g(4.12lb)1529.4g(3.37lb)F95finesand467.7g(1.03lb)452.8g(0.997lb)Gradedsand(ASTMC778)355.4g(0.783lb)344.1g(0.758lb)20-30sand(ASTMC778)355.4g(0.783lb)287.8g(0.634lb)S16coarsesand692.2g(1.52lb)444.7g(0.980lb)LWA(SSD)---183.6g(0.404lb)WaterinLWA---35.2g(0.0775lb)w/c=0.35Blendoffoursands(Ferraris)toimproveparticlepackingLWAaddedinsaturatedsurfacedry(SSD)conditionSSDspecificgravityof1.7Commercialcement–noparticleslargerthan30μmdiameterHydrationconductedat30oCmaintainedbycirculatingfluidfromatemperaturecontrolledbathAftermixing1dhydration2dhydrationSubtraction:1d–aftermixingAquaindicatesdryingRedindicateswettingAllimagesare13mmby13mmThree-dimensionalsubtractedimageof1dhydration–initialmicrostructureshowingwater-filledporesthathaveemptiedduringinternalcuring(4.6mmonaside)2-Dimagewithwaterevacuatedregions(pores)overlaidonoriginalmicrostructure(4.6mmby4.6mm)Four-DimensionalX-rayMicrotomographyQuantitativeAnalysis•Four-dimensionalimagesetsanalyzedtoestimatevolumeofwatermovingfromLWAtocementpasteduringfirst2dofhydration•Analysisbasedonchangesingreylevelhistogramwithtime•Resultscomparedtoconventionalmeasuresofhyd