hydration and microstructure development in accelerated cement pastes produced by spraying for th

1、HydrationMicrostructureDevelopmentinAcceleratedCementPastesProducedbySprayingftheEvaluationofShotcreteRenanPSalvad12SergioHPCavalaro1ngelRueda3AntonioDdeFigueiredo41.ConstructionEngineeringDepartmentPolytechnicUniversity

2、ofCataloniaBarcelona08034Spain2.CAPESFoundationMinistryofEducationofBrazilBrasliaDF70040020Brazil3.IndstriasQumicasdelEbroZaragoza50016Spain4.CivilConstructionEngineeringDepartmentPolytechnicSchoolofUniversityofSoPauloSo

3、Paulo05508010BrazilAbstractSprayedconcretediffersfromdinaryconcreteduetothemethodofapplicationtheuseofsetacceleratstopromoteimmediatestiffeningofthematrixrightaftermixing.Hydrationkiicsreactivityofacceleratingadmixturest

4、hemicrostructureofthecementitiousmatrixaregreatlydependentontheproductionmethod.Theobjectiveofthisstudyistoanalyzehowthesprayingprocessaffectsthepropertiesacteristicsofcementpastes.AtypeIcementanalkalifreeacceleratwhichp

5、romotesthefmationofettringitewereused.Pasteswereproducedinasmallscalesprayingmachinebyahmixingprocessfcomparisonpurposes.Hydrationwasanalyzedbyisothermalheatconductioncalimetryscanningelectronmicroscopyusingfreezedriedsa

6、mpleswasperfmedtoanalyzehowmicrostructureininfluencedbytheproductionmethod.Resultsshowedthattheapplicationofpastesbysprayingprovideinfluencesderateofaliteinitialhydratioaswellasthemicrostructureofthematrixwhichiscomposed

7、byshtermeamphousettringiteCSHcrystals.iginalityIndertoevaluatehydrationreactionsofcementwithshotcreteacceleratsthemicrostructuredevelopedbythosereactionsitisessentialthatthemethodfpastesproductionresemblethemethodusedinr

8、eallifeapplications.Byusingthesameproductionprocesstheacterizationoftheacceleratedcementmatrixismerealisticmayprovidemefeasibleexplanationsfthepropertiesthebehaviofsprayedconcreteinmacrostructures.Keywds:hydrationmicrost

9、ructurealkalifreeacceleratswetmixshotcrete.1Crespondingauth:Tel34934016516Fax34934011036Tab.1CementchemicalcompositionCompoundSiO2Fe2O3Al2O3CaOSO3Na2OK2OMgOTiO2P2O5MnOLOIContent(%)19.893.264.7462.623.530.130.991.950.220.

10、100.032.88Tab.2CementpropertiesPropertyInsolubleresidue(%)SpecificsurfaceBET(m2g)Result2.742.962.2.ExperimentalmethodologyTestswereperfmedincementpasteswithawatercementratioof0.32withtheadditionofthesuperplasticizeratthe

11、dosageof1.0%bycementweight.Ftheproductionofacceleratedpastesthealkalifreeacceleratwasaddedatthecontentof5.07.0%bycementweight.Allthematerialswereconditionedinaclimaticroomatthetemperatureof20oC1daypritotheiruse.Reference

12、pasteswhichcontainedonlycementwatersuperplasticizerwereproducedbyhmixingwhereasacceleratedpasteswereproducedbyhmixingbyspraying.Fthefirstmethodwatersuperplasticizerwerepremixedaddedtocementmixingthepastef45secondsusingav

13、texmixer.Thenthepasteobtainedwasstedinsealedplasticcontainerwhichwaskeptinachamberat20oC.Acceleratwasadded1houraftercementwaterweremixedhomogenizingthepastef15secondsusingaspatula.Thesecondmixingmethodconsistedinasprayin

14、gprocessusedtosimulateapplicationofsprayedconcreteinrealjobsites.Inthiscasethepastewaspumpedinasmallscalesprayingmachinetheacceleratwasaddedtothepasteatthenozzle.Inthiscaseacceleratwasalsoadded1houraftercementwaterweremi

15、xed.Pastesweresprayedin125mLsealableplasticcupswhichcontainedaround40gofpaste.Thisprocesswasperfmedinsideaclimaticchamberatthetemperatureof20oC.IsothermalcalimetrywasperfmedinanIcal4000calimeterat20oCf24hoursusing15gofce

16、mentpaste.Fhmixedpastessampleswereintroducedinthecalimeteraftermixingcementwaterremoved1hourlaterfacceleratadditionrelocatedinthecalimeterafteraccelerathomogenization.Howeversprayedpasteswereintroducedinthecalimeterright

17、afteraccelerataddition.FSEManalysiscementpasteswerefreezedriedusingliquidnitrogen15min3h12hafteracceleratwasadded.ThensampleswerecoveredwithcarbonfchemicalmicroanalysistheimageswereobtainedusingaJEOLJSM7100Fmicroscopeope

18、ratingat20kV.Fbothteststime“zero”wasconsideredasthetimewhenacceleratwasadded.3.ResultsDiscussion3.1.IsothermalcalimetryHeatflowenergyreleasecurvesobtainedwithhmixedsprayedpastesareshowninfigures12respectively.Infigure1th

19、efirstheatflowpeakoccurringinthehmixedpastesisduetothefirstcontactbetweencementwater.Thesecondpeakobservedat1houroccursduetotheacceleratadditiontheconsequentettringitefmation.Afterthatthemainhydrationpeakisobservedwherea

20、liteconsumptionptliteCSHprecipitationtakeplace.Inthesprayedpastestheheatflowpeakcausedbymixingcementwaterisnotpresentbecausesampleswereintroducedinthecalimeterafter1hourwhenacceleratwasadded.Itcanbeobservedthattheacceler

21、atedpastespresentamuchfasterhydrationwhencomparedtothereferencepastealsothatthehigherthedosageofacceleratthefasterthemainhydrationpeakoccurs.Aninterestingfactisthatthemaximumheatflowinthemainhydrationpeakreachedinsprayed

22、pastesisaround0.3mWgcementlowerthanthatinhmixedpasteswhichmightindicatethealitehydratesatalowerextentinpastesproducedbysprayingduringthefirst24hours.Thisprocesscanalsobeobservedinfigure2wherethecurvescrespondenttothespra

23、yedpastespresentalowerreactionrate(constantdecreaseinslope)from12hourson.ThehigheramountofettringitefmedinsprayedpastesindicatedbyahigherenergyreleasewhenacceleratisaddedinhibitalitedissolutionbecausethisAFtphaseiscrysta