混合料低温性能中的改性沥青性能理解

UnderstandingthePerformanceofModifiedAsphaltBindersinMixtures:Low-TemperaturePropertiesFHWA-RD-02-074byKevinD.StuartandJohnS.YoutcheffFOREWORDThisreportdocumentstheeffectsofpolymer-modifiedasphaltbindersonthelow-temperaturecrackingresistancesofasphaltmixtures.Anemphasiswasplacedonevaluatingtheperformancesofmixturescontainingpolymer-modifiedasphaltbinderswithidenticalSuperpaveperformancegrades,butvariedmodificationchemistries.ThisstudyispartofalargerstudytitledUnderstandingthePerformanceofModifiedAsphaltBindersinMixtures,whichispartiallyfundedthroughtheNationalCooperativeHighwayResearchProgram(NCHRP)Project90-07.TheobjectiveofNCHRPProject90-07istodetermineifasphaltbinderperformanceiscorrectlycapturedbytheSuperpaveasphaltbinderspecificationdevelopedunderthe1987through1993StrategicHighwayResearchProgramandmodifiedundersubsequentstudies.Thisreportwillbeofinteresttohighwaypersonnelwhousepolymer-modifiedasphaltbindersandSuperpave.TherecentlydevelopedSuperpavecriticalcrackingtemperature(Tcr)forasphaltbindersagreedwithmixtureperformance,exceptforoneasphaltbinderthatiscurrentlynotusedinpractice.Severalaggregatetypeswereincludedinthestudy.Theadditionofhydratedlimetooneoftheaggregatessignificantlyaffectedthelow-temperaturepropertiesofthemixture.Themechanismforthisisnotclearlyunderstoodandwillbeinvestigated.NOTICEThisdocumentisdisseminatedunderthesponsorshipoftheDepartmentofTransportationintheinterestofinformationexchange.TheU.S.Governmentassumesnoliabilityforitscontentsorusethereof.Thisreportdoesnotconstituteastandard,specification,orregulation.TheU.S.Governmentdoesnotendorseproductsormanufacturers.Tradeandmanufacturers=namesappearinthisreportonlybecausetheyareconsideredessentialtotheobjectofthedocument.ObjectiveT.PaulTeng,P.E.Director,OfficeofInfrastructureResearchandDevelopmentTheobjectiveofthisstudywastoevaluatethecrackingtemperaturesforasphaltbindersprovidedbytheBendingBeamRheometer(BBR)andThermalStressAnalysisRoutine(TSARTM).Low-temperaturemixturepropertiesprovidedbytheThermalStressRestrainedSpecimenTest(TSRST)wereusedtovalidatetheseasphaltbindertests.Anemphasiswasplacedonevaluatingtheperformancesofmixturescontainingpolymer-modifiedasphaltbinderswithidenticalSuperpaveperformancegrades(PG's)andsimilarbaseasphalts,butvariedmodificationchemistries.Thiswouldindicatewhattypesofmodificationprovidepropertiesthatare,orarenot,correctlycapturedbythecurrentSuperpaveasphaltbinderspecification.BBRandTSARTMTheBBRprovidestwocrackingtemperatures.Onetemperatureisbasedoncreepstiffness(S);theothertemperatureisbasedonthem-value.TheBBRtestisperformedinaccordancewithAmericanAssociationofStateHighwayandTransportationOfficials(AASHTO)TP1,titledMethodforDeterminingtheFlexuralCreepStiffnessofAsphaltBindersUsingtheBendingBeamRheometer(BBR).(1)TSARTMisacomputerprogramfromAbatech,Inc.,Doylestown,PA,thatperformsAASHTOPP42-01,StandardPracticeforDeterminationofLow-TemperaturePerformanceGrade(PG)ofAsphaltBinders.(2)Acriticalcrackingtemperature(Tcr)iscomputedusingdatafromboththeBBRandthedirecttension.ThestandardtestmethodforthedirecttensionisAASHTOTP3,titledDeterminingtheFracturePropertiesofAsphaltBinderinDirectTension(DT).(2)TSRSTTheTSRSTcoolsabeamofasphaltmixtureatarateof10癈elsius/hour(C/h)whilerestrainingitfromcontracting.Stressbuildsupinthebeamuntilitbreaks.Theresistancetolow-temperaturecrackingincreasesasthetemperatureneededforfracturedecreases.Thestressatfailurecanalsobeanalyzed.AdditionalinformationontheTSRSTisgiveninAASHTOTP10-93,titledMethodforThermalStressRestrainedSpecimenTensileStrength.(2)(Note:ThistestiscommonlycalledtheThermalStressRestrainedSpecimenTest.)AsphaltBindersElevenasphaltbindersweretested.Thisincludedoneair-blownasphaltandeightpolymer-modifiedasphaltbinders:(1)styrene-butadiene-styrene[SBS]Linear,(2)SBSLinearGrafted,(3)SBSRadialGrafted,(4)ethylenevinylacetate[EVA],(5)EVAGrafted,(6)Elvaloy,(7)ethylenestyreneinterpolymer[ESI],and(8)chemicallymodifiedcrumbrubberasphalt[CMCRA].Thereweretwocontrolasphaltbinders:anunmodifiedPG70-22andanunmodifiedPG64-28.Theeightpolymer-modifiedasphaltbindersincludeelastomericandplastomericmodifiers,somewiththesamemodifierbutdifferentgeometries(linearvs.radialgeometries).Thetermgraftedincludesanymodeofchemicallyreactingapolymerwithanasphaltbinder,forexample,vulcanization.ThetargetPGforthepolymer-modifiedasphaltbinderswasPG73-28.ThePG64-28asphaltbinder,andaPG52-34asphaltbinderfromthesamecrudesource,weremodified.Theair-blownasphaltwasoriginallythePG52-34asphaltbinder.ExperimentUsingDiabaseAggregateThemixturesconsistedofdiabaseaggregateandthe11asphaltbinders.Aminimumofthreereplicatebeamsat7.0?0.5-percentairvoidsweretestedbytheTSRST.Themixturesweresubjectedto2hofshort-termovenaging(STOA)at135癈beforecompaction.TwohoursofSTOAwasfoundtoprovidetheaverageamountofagingforpavementsconstructedin1993foraFederalHighwayAdministration(FHWA)Superpavevalidationstudy.(3)Itwasbasedonpavementsamplestaken3monthsafterconstruction.Mixtureteststhatmeasurelow-temperaturecrackingresistanceareoftenperformedonspecimensthat