Perforation-of-concrete-slabs-with-48-MPa-(7-ksi)-

Int.JImpactEnqnqVol.12.No.1,ppI-7,19920734~743X/92$5.00+0.00PrintedmGreatBritaint1992PergamonPressplcPERFORATIONOFCONCRETESLABSWITH48MPa(7ksi)AND140MPa(20ksi)UNCONFINEDCOMPRESSIVESTRENGTHSS.J.HANCHAK,*M.J.FORRESTAL,tE.R.YOUNGtandJ.Q.EHRGOTT~*UniversityofDaytonResearchInstitute,Dayton,OH45469,U.S.A.;tSandlaNationalLaboratories,Albuquerque,NM87185,U.S.A.;:~WaterwaysExperimentStation,Vicksburg,MS39180,U.S.A.(Recewed1May1990;inrevisedform3September1991)Summary--Weconductedperforationexperimentswith25.4-mmdiameter,0,50-kg,3.0-caliber-radius-head,ogwal-noserodsand178-mm-thickconcreteslabswith48MPa(7ks1)and140MPa(20ksi)unconfinedcompressivestrengths.Forimpactvelocitiesbetween300and1100m/s,ourdatashowedthatresidualvelocitiesforthe140MPaconcretewerelessthan200lowerthanthatforthe48MPaconcrete.Thus,forafactorofthreeincreaseinunconfinedcompressivestrength,wemeasuredrelativelyminorchangesinballisticperforationperformance.Weexplainedtheseresultsqualitativelywithpost-testobservationsandtriaxialmaterialexperimentsw~ththe48and140MPaconcretematerials.INTRODUCTIONGodfrey[1-Idiscussesrecentadvancesinconcretematerialsusedforcolumnsinhigh-risestructures.Inparticular,Godfreynotesthatsomepreconstructiontestpourshaveshownthat131MPa(19ksi)unconfinedcompressionstrengthsareobtainedat56daysafterthepour.Bycontrast,therecentpaperbyBrown[2]onballisticprotectionreportsresultsforconcreteslabslimitedtothe21-34MPa(3-5ksi)strengthrange.MotivatedbyGodfrey'spaper[1],weplannedandexecutedanexperimentalprogramtostudytheperforationof48MPa(7ksi)and140MPa(20ksi)strengthconcreteslabs.The48MPa(7ksi)concreteistypicallyusedfortheconstructionofstructuralmembers,soweobtainedballisticperforationdatafortypicalandhigh-strengthconcreteslabs.Comparisonofballisticperforationdataforbothconcretematerialsshowedthattheresidualvelocitiesforthe140MPaconcretewerelessthan20%lowerthanthatforthe48MPaconcrete.CONCRETEMIXDESIGNANDMATERIALPROPERTIESBriceSimons,§innovaterofthehigh-strengthconcretedescribedinthearticlebyGodfrey[1],designedtheconcretemixesandcastedthetargetsandmaterialtestcylindersfortriaxialmaterialexperiments.Toachieve140MPa(20ksi)unconfinedcompressivestrength,themixdesignrequiresalowwater-to-cementratio,silicafume,ahighcementcontent,superplasticizersandthestrongestavailablecementandaggregates.Reducingthewater-to-cementratioto0.22isthemostimportantfactorforachievinghighstrength.Superplasticizersmustbeusedforconcreteworkability,andsilicafumecreatesadensercementpasteandincreasesunconfinedcompressivestrengthby250.Simonsspecifiesthemaximumaggregatesizestobe9.5mm(0.375in.).Table1presentsthecomponentdensityratiosforeachconcretedesign.Thecomponentsarenormalizedtothecementdensity,sothecomponentdensityratioforcementis1.Ifwecomparethe140MPa(20ksi)and48MPa(7ksi)concretesonatotalweightbasis,thehigherstrengthconcretehas380morecementand340lesswater.§SimonsEngineeringServices,Seattle,Washington,U.S.A.S.J.HANCHAKetal.TABLE1.COMPONENTDENSITYRATIOSFOR48MPa(7ksi)AND140MPa(20ksi)UNCONFINEDCOMPRESSIVESTRENGTHCONCRETES.GRAVELWASSTEILACOONGLACIALTILLWITHMOHSHARDNESSOF6.6[3]Componentdensityratios48MPa(7ksi)140MPa(20ksi)Cement1.01.0Flyash0.00.12Sihcafume0.00.10Water0.410.27Sand2.241.30Gravel3.14216Wetdensity2440kg/m32520kg/m3tmm-i610mm*..o~..IJiI/~178mm-_++'+.'~i~127--,~-12.7mm76.2mm76.2mm76.2mmFIG1.Targetgeometrywithlocationofthesteelreinforcement(5.69mmdiameter).Figure1showsthetargetgeometryandlocationofthereinforcement.Targetsforbothmixdesignsusedthreelayersofasquare-patternreinforcement.Thereinforcingrodswere5.69mm(0.224in.)diametersteelwire.OtherdetailsaredimensionedinFig.1.Concretecylinderswithlength127mm(5.0in.)anddiameter63.5mm(2.5in.)werecastfortriaxialmaterialtests.Ehrgott[4]describesthehigh-pressuretriaxialtestprogramfortheseconcretematerials,andwesummarizetheresultsinthispaper.Thesetestsareconductedintwophases:isotropiccompressionfollowedbytriaxialshear.Theconcretecylindersareloadedwithaxialstressa~andradialstresstrr.Forisotropiccompressiona,=at,sopressureisgivenbyp=1/3(a,+2a~).Forisotropiccompressionoruniformpressure,deformationmeasurementsofthelengthanddiameterchangesduringloadingwereperformed.Figure2showsresultsfromisotropiccompressionexperimentsthatmeasurepressureversusvolumetricstrain.Weshowthreedatacurvesforthe48MPa(7ksi)concreteandbracketresultsfromthreedatacurvesforthe140MPa(20ksi)concrete.Webracketthe140MPa(20ksi)databecausetheactualdataplotsaretooclosetoeachothertoplotonthescaleinFig.2.Perforationofconcreteslabs36O0IIIIIII500/:400-;~-.,200.,7m.....120ksI)(7ksl)o~IIIIIII00.0:20.040.06VOLUMETRICSTRAINFIG2.Pressureversusvolumetricstrain.008500Q.4001-30Op-ZWI--200¢/)EuJq-100U~IIIIII.....140MPa(20ksi).q48MPa(7ksl)IN....~BL...........IP'•ILIIII100200300400500600PRESSURE,p(MPa)700FIG3.Shearstrengthversuspressure.Forthetriaxialsheartests,theconcretespecimensarefirstloadedwithisotropiccompression,andthentheaxialstressaaisincreasedwhiletheradialstressarisheldconstant.Valuesofthemaximumstressdifferencer=(r,-~rr)orshearstrengthversuspressurep=1/3(ix,+2~r)aregiveninFig.3.Da