AASHTO-T-313-2008

TS2bT313-1AASHTOStandardMethodofTestforDeterminingtheFlexuralCreepStiffnessofAsphaltBinderUsingtheBendingBeamRheometer(BBR)AASHTODesignation:T313-081.SCOPE1.1.Thistestmethodcoversthedeterminationoftheflexuralcreepstiffnessorcomplianceofasphaltbindersbymeansofabendingbeamrheometer.Itisapplicabletomaterialhavingaflexuralstiffnessvaluefrom20MPato1GPa(creepcompliancevaluesintherangeof50nPa–1to1nPa–1)andcanbeusedwithunagedmaterialorwithmaterialagedusingT240(RTFOT)and/orR28(PAV).Thetestapparatusisdesignedfortestingwithinthetemperaturerangefrom–36to0°C.1.2.Testresultsarenotvalidforbeamsofasphaltbinderthatdeflectmorethan4mm,orlessthan0.08mm,whentestedinaccordancewiththismethod.1.3.Thisstandardmayinvolvehazardousmaterials,operations,andequipment.Thisstandarddoesnotpurporttoaddressallofthesafetyconcernsassociatedwithitsuse.Itistheresponsibilityoftheuserofthisproceduretoestablishappropriatesafetyandhealthpracticesandtodeterminetheapplicabilityofregulatorylimitationspriortouse.2.REFERENCEDDOCUMENTS2.1.AASHTOStandards:M320,Performance-GradedAsphaltBinderR28,AcceleratedAgingofAsphaltBinderUsingaPressurizedAgingVessel(PAV)T40,SamplingBituminousMaterialsT240,EffectofHeatandAironaMovingFilmofAsphalt(RollingThin-FilmOvenTest)2.2.ASTMStandards:C670,PracticeforPreparingPrecisionandBiasStatementsforTestMethodsforConstructionMaterialsC802,ConductinganInterlaboratoryTestProgramtoDeterminethePrecisionofTestMethodsforConstructionMaterialsE77,StandardTestMethodforInspectionandVerificationofLiquid-in-GlassThermometersE220,MethodforCalibrationofThermocouplesbyComparisonTechniques2.3.DeutcheIndustrieNorm(DIN)Standards:43760,PlatinumResistanceThermometerTS2bT313-2AASHTO3.TERMINOLOGY3.1.Definitions:3.1.1.asphaltbinder—anasphalt-basedcementthatisproducedfrompetroleumresidueeitherwithorwithouttheadditionofnon-particulateorganicmodifiers.3.1.2.physicalhardening—atime-dependentstiffeningofasphaltbinderthatresultsfromthetime-delayedincreaseinstiffnesswhentheasphaltbinderisstoredatlowtemperatures.Theincreaseinstiffnessduetophysicalhardeningisreversiblewhenthetemperatureisraised.3.2.DescriptionsofTermsSpecifictoThisStandard:3.2.1.flexuralcreep—atestinwhichasimply-supportedasphaltbinderprismaticbeamisloadedwithaconstantloadatitsmidpointandthedeflectionofthebeamismeasuredwithrespecttoloadingtime.3.2.2.measuredflexuralcreepstiffness,Sm(t)—ratioobtainedbydividingthemaximumbendingstressinthebeambythemaximumbendingstrain.3.2.3.estimatedcreepstiffness,S(t)—thecreepstiffnessobtainedbyfittingasecondorderpolynomialtothelogarithmofthemeasuredstiffnessat8.0,15.0,30.0,60.0,120.0,and240.0sandthelogarithmoftime.3.2.4.flexuralcreepcompliance,D(t)—ratioobtainedbydividingthemaximumbendingstraininthebeambymaximumbendingstress.D(t)istheinverseofS(t).S(t)hasbeenusedhistoricallyinasphalttechnologywhileD(t)iscommonlyusedinstudiesofviscoelasticity.3.2.5.m-value—absolutevalueoftheslopeofthelogarithmofthestiffnesscurvesversusthelogarithmofthetime.3.2.6.contactload—loadrequiredtomaintainpositivecontactbetweenthebeamandtheloadingshaft;35±10mN.3.2.7.seatingload—loadof1-sdurationrequiredtoseatthebeam;980±50mN.3.2.8.testload—loadof240-sdurationrequiredtodeterminethestiffnessofmaterialbeingtested;980±50mN.3.2.9.testingzerotime,s—timeatwhichthesignalissenttothesolenoidvalvetoswitchfromzeroloadregulator(contactload)tothetestingloadregulator(testload).4.SUMMARYOFTESTMETHOD4.1.Thebendingbeamrheometermeasuresthemid-pointdeflectionofasimplysupportedbeamofasphaltbindersubjectedtoaconstantloadappliedtothemid-pointofthebeam.Thedeviceoperatesonlyintheloadingmode;recoverymeasurementsarenotobtained.TS2bT313-3AASHTO4.2.Atestbeamisplacedinthecontrolledtemperaturefluidbathandloadedwithaconstantloadfor240s.Thetestload(980±50mN)andthemidpointofdeflectionofthebeamaremonitoredversustimeusingacomputerizeddataacquisitionsystem.4.3.Themaximumbendingstressatthemidpointofthebeamiscalculatedfromthedimensionsofthebeam,thespanlength,andtheloadappliedtothebeamforloadingtimesof8,15,30,60,120,and240seconds.Themaximumbendingstraininthebeamiscalculatedforthesameloadingtimesfromthedimensionsofthebeamandthedeflectionofthebeam.Thestiffnessofthebeamfortheloadingtimesspecifiedaboveiscalculatedbydividingthemaximumstressbythemaximumstrain.4.4.Theloadanddeflectionat0.0and0.5sarereportedtoverifythatthefull-testingload(980±50mN)duringthetestisappliedwithinthefirst0.5s.Theyarenotusedinthecalculationofstiffnessandm-valueandshouldnotbeconsideredtorepresentmaterialproperties.Therisetimeoftheload(timetoapplyfullload)canbeaffectedbyimproperoperationofthepressureregulators,improperairbearingpressure,malfunctioningairbearing(friction),andotherfactors.Byreportingthe0.0andthe0.5ssignals,theuserofthetestresultscandeterminetheconditionsoftheloading.5.SIGNIFICANCEANDUSE5.1.Thetesttemperatureforthistestisrelatedtothetemperatureexperiencedbythepavementinthegeographicalareaforwhichtheasphaltbinderisintended.5.2.Theflexuralcreepstiffnessorflexuralcreepcompliance,determinedfromthistest,describesthelow-temperature,stress-strai