Comparative flexural behavior of Hybrid Ultra High Performance Fiber Reinforced Concrete

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ComparativeflexuralbehaviorofHybridUltraHighPerformanceFiberReinforcedConcretewithdifferentmacrofibersDongJooKima,⇑,SeungHunParka,GumSungRyub,KyungTaekKohbaDepartmentofCivilandEnvironmentalEngineering,SejongUniversity,98Gunja-Dong,Gwangjin-Gu,Seoul143-747,RepublicofKoreabKoreaInstituteofConstructionTechnology,2311Daewha-Dongilsan-Gu,Goyang-Si,Gyeonggi-Do411-712,RepublicofKoreaarticleinfoArticlehistory:Received24February2011Receivedinrevisedform15April2011Accepted19April2011Availableonline23May2011Keywords:HybridMacrofiberMicrofiberStraincapacityDeflectioncapacityUltraHighPerformanceFiberReinforcedConcreteabstractTheflexuralperformanceoffourHybrid(H-)UltraHighPerformanceFiberReinforcedConcretes(UHPFRCs)withdifferentmacrofiberswasinvestigatedaccordingtoASTMstandardsC1018-97andC1609/C1609M-05.Fourmacrofiberswerelongsmooth(LS-)steelfiber,twotypesofhooked(HA-andHB-)steelfibers,andtwisted(T-)steelfiberswhileonetypeofmicrofiber,shortsmooth(SS-)steelfiber,wasblended.Theenhancementsinmodulusofrupture,deflectioncapacityandenergyabsorptioncapac-ityweredifferentaccordingtothetypesofmacrofiberastheamountofmicrofiberblendedincreased.TheorderofflexuralperformanceofH-UHPFRCaccordingtothetypesofmacrofiberwasasfollows:HB->T->LS->HA-fiber.TheinfluenceofstraincapacityintensionontheflexuralperformanceofH-UHPFRCwasalsoexamined.ThedeflectioncapacityandtheratiobetweenflexuralstrengthandtensilestrengthweredependentuponthestraincapacityofH-UHPFRC.Ó2011ElsevierLtd.Allrightsreserved.

1.IntroductionMuchresearchhasbeenconductedtoenhancethetensilestrengthandductilityofUltraHighPerformanceFiberReinforcedConcrete(UHPFRC)[24,8,16,7,23,10,11,32].TheadvantagesofUHPFRCincludehigherdurability,ductilityandstrengthincom-parisonwithnormalconcreteandFiberReinforcedConcrete(FRC)duetoitsextremelylowporosity;densematrix;highten-sile/compressivestrength;and,ductiletensilebehavior.Incom-parisonwithnormalsteelreinforcedconcrete,theapplicationofUHPFRCisexpectedtoimprovetheresistanceofbuildingsandinfrastructureunderextrememechanicalandenvironmentalloads.However,thecostof1%volumecontentoffiberappliedinUHPFRCisgenerallyhigherthanthatofmatrix.Thus,itisimpor-tanttominimizetheamountsoffiberwithoutscarifyingthesupe-riorperformanceofUHPFRC.MuchinterestisnowfocusedonbothminimizingtheamountsoffiberandmaximizingtheperformanceofUHPFRC.ThetensileorflexuralperformanceofUHPFRCisinfluencedbymanymaterialparameters.Theparametersincludestrength,stiff-ness,shape,aspectratio,andPoisson’sratiooffibers;thestrength,stiffness,andshrinkageofmatrix;and,thephysio-chemicalandfrictionalbondpropertiesattheinterfacebetweenfiberandmatrix.UndertheassumptionthatanidenticalUltraHighPerfor-manceConcrete(UHPC)matrixisused,thetypeoffiberisthemostgoverningfactoramongtheseveralparametersmentionedabove.Thus,thematerial,geometry,andvolumecontentsoffibershouldbeverycarefullydeterminedtoimprovetheflexuralperformanceofUHPFRC.ToimprovetheflexuralperformanceofUHPFRC,oneofthepromisingmethodsistoblendtwoorthreedifferentfibersto-getherinamatrix,becausethemacroandmicrofibersplayaroleattwodifferentlevels,materialandstructural,accordingtothelengthanddiameteroffibers[24,23].Therehasbeenmuchre-searchonthedevelopmentofHybridFiberReinforcedConcrete(H-FRC)withnormalcompressivestrengthandconsequently,itwasfoundthatthefiberblendinginnormalstrengthmatricespro-ducedfavorableblendingeffectonthemechanicalperformanceincludingtensilestrengthandductilityincomparisonwithFRCwithonetypeoffiber[22,33,14,5,4,1,27].Ingeneral,H-FRCem-ploysalongandthickfiberasmacrofiberandashortandthinfiberasmicrofiber.Fibersblendedtogetherinabrittlematrixcanbeclassifiedintomacroandmicrofibersaccordingtheroleoffibersinabrittlematrix[24,23].However,mostresearchonH-UHPFRChasbeenfocusedonfindingtheoptimumvolumecontentsofmicrofiberblendedwithonetypeofmacrofibertoimprovetensile/flexuralstrengthandductility[30,6,9,17,26].Thus,itisdifficulttofindanyinformationabouttheinfluenceofmacrofibersontheflexuralperformanceofH-UHPFRC.0950-0618/$-seefrontmatterÓ2011ElsevierLtd.Allrightsreserved.doi:

10.1016/j.conbuildmat.2011.04.051⇑Correspondingauthor.Tel.:+82234083820;fax:+82234084332.E-mailaddresses:djkim75@sejong.ac.kr(D.J.Kim),parksh8179@naver.com(S.H.Park),ryu0505@kict.re.kr(G.S.Ryu),ktgo@kict.re.kr(K.T.

Koh).ConstructionandBuildingMaterials25(2011)4144–4155ContentslistsavailableatScienceDirectConstructionandBuildingMaterials

journalhomepage:www.elsevier.com/locate/con

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ildmatRecently,theinfluenceofmacrofibersonthetensilebehaviorofH-UHPFRChasbeeninvestigatedbyauthors[21].Astheamountofmicrofiberblendedincreases,theimprovementofthepostcrack-ingstrength,straincapacityandmultiplecrackingbehaviorsisverydifferentaccordingtothetypesofmacrofiber.SincetheflexuralbehaviorofFiberReinforcedCementitiousComposites[FRCC]isdependentonthetensilestress–strainre-sponseofFRCC,themaximumequivalentbendingstrength,deflec-tioncapacityandenergyabsorptioncapacityofH-UHPFRCwouldbehighlyinfluencedbybothstraincapacity(materialductility)andpostcrackingstrength(materialstrength)ofH-UHPFRC[19,13].Theobjectiveofthisresearchistoinvestigatetheflexuralper-formanceofH-UHPFRCaccordingtodifferenttypesofmacrofiber.Thedetailedobjectivesare:(1)toinvestigatetheinfluenceofdif-ferentmacrofibersontheflexuralbehaviorofH-UHPFRC,(2)toinvestigatetheinfluenceofthemicrofibervolumecontentsontheflexuralbehaviorofHybridUHPFRC,and(3)tocorrelatethetensileresponse(materialductility)andflexuralresponse(struc-turalperformance)ofH-UHPFRC.2.ResearchsignificanceVerylittleinformationisavailableabouttheinfluenceofthetypesofmacrofiberontheflexuralbehaviorofhybridUHPFRC(H-UHPFRC).ThisresearchprovidesusefulexperimentaldataontheinfluenceofdifferentmacrofibersblendedwithmicrofibersontheflexuralperformanceofH-UHPFRCtooptimizefiberblend-inginhybridsystems.Furthermore,thisresearchhighlights