Performance of Recycled Hot Mix Asphalt Mixtures

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  • 8/9/2019 Performance of Recycled Hot Mix Asphalt Mixtures

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    PERFORMANCEOFRECYCLEDHOTMIXASPHALTMIXTURES

    By

    PrithviS.Kandhal

    ShridharS.RaoDonaldE.WatsonBradYoung

    PaperpublishedinTransportationResearchBoard,TransportationResearchRecord1507,1995

    277TechnologyParkway Auburn,AL36830

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    PERFORMANCEOFRECYCLEDHOTMIXASPHALTMIXTURES

    By

    PrithviS.Kandhal

    AssistantDirectorNationalCenterforAsphaltTechnology

    AuburnUniversity,Alabama

    ShridharS.Rao

    GraduateStudentAuburnUniversity,Alabama

    DonaldE.Watson

    AssistantStateMaterialsandResearchEngineerGeorgiaDepartmentofTransportation

    BradYoung

    AssociateResearchEngineerGeorgiaDepartmentofTransportation

    PaperpublishedinTransportationResearchBoard,TransportationResearchRecord1507,1995

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    DISCLAIMER

    Thecontentsofthisreportreflecttheviewsoftheauthorswhoaresolelyresponsibleforthefactsandtheaccuracyofthedatapresentedherein.ThecontentsdonotnecessarilyreflecttheofficialviewsandpoliciesoftheNationalCenterforAsphaltTechnologyofAuburnUniversity.Thisreportdoesnotconstituteastandard,specification,orregulation.

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    ABSTRACT

    TheGeorgiaDepartmentofTransportation(GDOT)hasbeenconstructingrecycledasphalt

    pavementsroutinelyforaboutfouryears.Thisresearchprojectwasundertakentoevaluatetheperformanceofrecycledpavementsincomparisontovirgin(control)asphaltpavements.

    Fiveprojects,eachconsistingofarecycledsectionandacontrolsection,weresubjectedto

    detailedevaluation.In-situmixproperties(suchaspercentairvoids,resilientmodulusandindirecttensilestrength),recoveredasphaltbinderproperties(suchaspenetration,viscosity,G*/sin*andG*sin*),andlaboratoryrecompactedmixproperties(suchasGyratoryStabilityIndexandconfined,dynamiccreepmodulus)weremeasured.Apairedt-teststatisticalanalysisindicatednosignificantdifferencesbetweenthesepropertiesofvirginandrecycledmixpavementswhichhavebeeninservicefrom1to2years.

    Tenadditionalvirginmixpavementsand13additionalrecycledpavementswerealsoevaluated

    astwoindependentgroups.Nostatisticallysignificantdifferenceswerefoundbetweenthe

    recoveredasphaltproperties(penetrationandviscosity)ofthesevirginandrecycledpavementsinservice.

    ThecurrentGDOTrecyclingspecificationsandmixdesignproceduresappeartobesatisfactory

    basedontheresultsofthisstudy.

    KeyWords:HotMixAsphalt,AsphaltConcrete,HotRecycling,Performance,Aging

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    PERFORMANCEOFRECYCLEDHOTMIXASPHALTMIXTURES

    PrithviS.Kandhal,ShridharS.Rao,DonaldE.Watson,andBradYoung

    INTRODUCTIONHotmixrecyclingofasphaltpavementsisincreasinglybeingusedasoneofthemajorrehabilitationmethodsbyvarioushighwayagenciesallovertheUnitedStates.Besidesgeneralsavingsincostsandenergyexpended,italsosavesournaturalresourcesandenvironment.TheGeorgiaDepartmentofTransportation(GDOT)hasbeenconstructingrecycledhotmixasphalt(HMA)pavementsroutinelyforaboutfouryears.MostoftherecycledpavementsinGeorgiahavebeenconstructedusingAC-20asphaltcementtypicallywith10to25%reclaimedasphaltpavementmaterial,whereasvirginHMApavementsaregenerallyconstructedusingAC-30asphaltcement.ItwasfeltnecessarytoevaluatetheperformanceoftheserecycledpavementsincomparisontovirginHMApavementsconstructedduringthesameperiod.ThiswoulddeterminewhethertherecycledHMApavementshaveperformedsimilartothevirginHMApavements.Itwouldalsoprovideinformationforadjustingthespecificationandmixdesignmethodforrecycledmixtures,ifneeded.

    OBJECTIVES

    Theprimaryobjectivesofthisprojectareasfollows:

    1.Evaluatetheperformanceofin-servicerecycledandvirgin(control)HMApavementsfromthesameprojectbothvisuallyaswellasinthelaboratory,

    2.ComparetheperformanceofrecycledHMAprojectswiththatofvirgin(control)HMAprojects,and

    3.ReviewGDOT'spresentrecyclingspecificationsandrecommendchangeswherenecessary.

    Thisstudywasdividedintotwotasks.Task1involvedidentifyingexistingfieldprojectswhichhaveusedbothrecycledandvirgin(control)mixesonthesameprojectandconductingadetailedcomparativeevaluation.Task2consistedofevaluatingatleast10recycledHMApavementsandatleast10virginmixpavementsconstructedindependentlythroughoutthestateduringthelast2-3years.Thepropertiesofthebindersrecoveredfromthemixturesoftheaboveprojectsformedadatabaseforcomparativepurposes.

    Theworkforeachtaskinvolvedcollectingconstructiondataofalltheprojects,visualevaluation

    ofthein-servicepavements,sampling,andextensivelaboratorytestingofthefieldcorestakenfromeachproject.

    REVIEWOFLITERATURE

    ResearchcarriedoutbyLittleandEpps(1),Littleetal.(2),Brown(3),Meyersetal.(4),andKandhaletal.(5)hasindicatedthatthestructuralperformanceofrecycledmixesisequalandinsomeinstancesbetterthanthatoftheconventionalmixes.

    Thepropertiesoftherecycledmixturearebelievedtobemainlyinfluencedbytheaged

    reclaimedasphaltpavement(RAP)binderpropertiesandtheamountofRAPinthemixture.Kiggunduetalwshowedthatmixturespreparedfromtherecycledbinderblendsgenerallyageataslowerratethanvirginmixtures.ThismaybeduetothefactthattheRAPbinderhasalreadyundergoneoxidationwhichtendstoretardtherateofhardening(4,6)KiggunduandNewman(7)haveindicatedthattherecycledmixtureswithstoodtheactionofwaterbetterthanthevirginmixtures.DunningandMendenhall(8)havealsoshownthatthedurabilityofrecycledasphaltconcretemixturesisgreaterthanthatoftheconventionalmixtures.

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    TheamountoftheRAPusedinarecycledmixturedependsonthetypeofhotmixplantbeing

    usedforpreparingthemixandalsoonenvironmentalconsiderations.However,thegradationofaggregateinRAP(especiallythematerialpassingNo.200sieve)canalsobeamajorlimitingfactor.ThespecifiedmaximumpermissibleamountsofRAPvaryfromstatetostate.The

    GeorgiaDepartmentofTransportationlimitstheamountofRAPto40percentofthetotalrecycledmixtureforcontinuoustypeplantsandto25percentforbatchtypeplants(9).SomestatesallowhigherpercentagesofRAPforallplants.AccordingtotheGDOTspecificationtheRAPbinderwhenblendedwithvirginasphaltcementshouldgiveaviscositybetween6,000poisesto16,000poisesafterthethinfilmoventest.

    SAMPLINGANDTESTINGPLAN(TASK1)

    Onlyfiveexistingfieldprojectscouldbeidentifiedforthistask,whichhadbothrecycledandvirginHMAmixturesonthesameprojectinthewearingcourse.Theselectionoftheseprojectsassuredthattherecycledandthevirginsectionsusedthesamevirginaggregatesinthemixtures,wereproducedbythesameHMAplant,wereplacedandcompactedbythesameequipmentand

    crew,andweresubjectedtothesametrafficandenvironmentduringservice.Theprojectdetailsofboththerecycledandthecontrol(virgin)wearingcoursemixturesforthe

    fiveprojectsaregiveninTable1.Asshowninthetable,GeorgiaDOTalsousesAC-20Special(designatedasAC-20S)whichisrequiredtohaveapenetrationrangeof60to80.

    Table1.ProjectConstructionDetails(Task1)

    VirginAsphaltCement MixPropertiesProperties

    Site County Section Ageyrs RAP Grade Viscosity Pen. Asphalt %AirNo. % (60C)Pa-s 25C Content Voids

    (%) (mat)

    18C Coffee Virgin 1.50 0 AC-30 299 *** 6.0 9.018R Coffee Recycled 1.50 15 AC-30 299 *** 5.7 9.3

    22C Ware Virgin 1.75 0 AC-30 270 *** 6.0 6.6

    22R Ware Recycled 1.75 10 AC-20S 191 *** 5.7 6.9

    23C Chatham Virgin 1.50 0 AC-30 281 *** *** ***

    23R Chatham Recycled 1.50 25 AC-20 199 *** 5.4 6.5

    25C Emmanuel Virgin 2.25 0 AC-30 297 *** 5.8 7.9

    25R Emmanuel Recycled 2.25 20 AC-20 206 *** 57 7.4

    28C Columbia/ Virgin 1.50 0 AC-30 305 *** 6.0 8.3

    Richmond

    28R Columbia/ Recycled 1.50 20 AC-30 305 *** 5.8 7.8Richmond

    ***Datanotavailable

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    Therecycledandthecontrolsectionsforallfiveprojectswerevisited.Arepresentative150m

    (500ft)longtestareawasselectedineachsectionfordetailedevaluation.Thepavementwasvisuallyevaluatedforsurfacedistresssuchasrutting,raveningandweathering,alligator(fatigue)cracking,andtransversecracking.

    Atotalofeight101-mm(4-inch)diametercoresandfour152-mm(6-inch)diametercoreswereobtainedfromeach150-m(500-ft)representativesectionfromtheoutsidewheeltrack.Coreswereobtainedatanintervalof30-m(100-ft).

    LaboratorytestswereconductedonthefieldcoresaccordingtotheflowchartshowninFigure

    1.Allthefieldcoresweresawedtorecoveronlytherecycledorthecontrol(virgin)wearingcourseportionofthepavement.

    Figure1.CoreTestingPlan(Task1)

    Themixfromthe152-mm(6-inch)diametercoreswasreheatedto133C(300F)andrecompactedinthelaboratoryusingtheU.S.CorpsofEngineersGyratoryTestMachine(GTM).Thiswasdonetoevaluatetheruttingpotentialandshearpropertiesoftherecycledandthecontrolmixes.Propertiessuchasgyratorystabilityindex(GSI),gyratoryelasto-plasticindex(GEPI),androllerpressure,whicharediscussedlater,weredeterminedasthemixwas

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    compacted.Airvoidcontentsofthecompactedspecimenswerealsoobtained.Confined,

    dynamiccreeptestswereperformedontherecompactedspecimensat60C(140F),138kPa(20psi)confiningpressureand828kPa(120psi)verticalpressure.Dynamicloadingwasappliedforadurationofonehourandthenthespecimenwasallowedtorecoverfor30minutes.

    TheextractionoftheagedasphaltcementfromtheHMAmixtureswasaccomplishedbytheASTMD2172(MethodA)procedureusingtrichloroethylene.TheasphaltcementfromthesolutionwasrecoveredusingtheRotovaporapparatusasrecommendedbytheSHRPprogram.Therecoveredasphaltcementwastestedforviscosityat60C(140F)andpenetrationat25C(77F).Also,thecomplexshearmodulus(G*)andthephaseangle(*)oftherecoveredasphaltbinderweredeterminedusingadynamicshearrheometer(DSR)accordingtotheAASHTOPerformanceGradedBinderSpecification(MP1)fortheStateofGeorgia.Testtemperaturesof64C(148F)and22C(72F)wereusedtodeterminethepotentialforruttingandfatiguecracking,respectively,ascontributedbythebinder.

    Thetestsconductedonthe101-mm(4-inch)diameterfieldcoreswere(a)airvoidcontent,(b)

    resilientmodulusat25C(77F),andGindirecttensiletestat25C(77F).TESTDATA(TASK1)

    Asmentionedearlier,visualevaluationoftherecycledandthecontrolsectionswascarriedout.AsummaryoftheobservationsmadeduringthepavementevaluationispresentedinTable2.Theseresultswereanalyzedandquantifiedtocomparetherelativeperformanceofrecycledandcontrolsections.LaboratorytestswereconductedonthecoresobtainedfromtheprojectsitesaccordingtothetestingplanshowninFigure1.

    In-situMixProperties

    Figure2showsthetestdataobtainedonthefieldcoresfromthe5projects(bothrecycledand

    controlsections).Thetestdataincludesairvoidcontent,resilientmodulusat25C(77F),andindirecttensilestrengthat25C(77F).

    RecompactedMixProperties

    ThemixobtainedfromthefieldcoreswasheatedandrecompactedintheGTMasmentionedearlier.BasedonNCAT'sexperience,averticalpressureof828kPa(120psi)and10initialgyrationanglewasused.Thecommongyratoryindicesandshearpropertiessuchasgyratorystabilityindex(GSI),gyratoryelasto-plasticindex(GEPI),androllerpressurewereobtained(10).

    Figure3givestheaveragerecompactedmixpropertiessuchasairvoidcontent,GEPI,GSIand

    rollerpressure.Figure4showstheaveragetestdataobtainedfromtheconfined,dynamiccreep

    tests.

    RecoveredAsphaltBinderProperties

    Therecoveredasphaltcementwastestedforpenetrationat25C(77F)andabsoluteviscosityat60C(140F).TheresultsfromthesetestsareshowninFigure5.Twosamplesweretestedfromeachsectionand,therefore,thetestdatareportedistheaverageoftwotests.

    Sincethemainconcernofthisprojectisperformance,itwasdecidedtodeterminethe

    rheologicalpropertiesoftherecoveredbinderusingperformancebasedSHRPbindertestssuchasthedynamicshearrheometer(DSR).ThistestingwascarriedoutaspertheSHRPasphaltbinderspecificationproposedfortheStateofGeorgia.Theviscoelasticbehaviorofthe

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    Table2.PavementSurfaceEvaluation(Task1)

    SiteNo. County MixType AverageRut Raveling& Alligator Transverse Longitudinal OtherSurfaceDepth(inch) Weathering Cracking Cracking Cracking Distress

    18C Coffee Virgin 0.069 None None Low None WBLhasmore

    transversecracks

    18R Coffee Recycled 0.069 None None None None None

    22C Ware Virgin 0.069 None None None None None

    22R Ware Recycled 0.063 None None None None None

    23C Chatham Virgin 0.044 None None None None None

    23R Chatham Recycled 0.066 None None None None None

    25C Emmanuel Virgin 0.009 None None Low Low Map

    (continuous) Cracking

    25R Emmanuel Recycled 0.063 None None Low Low Long.Refl.

    (continuous) Crack

    28C Columbia/ Virgin 0.013 None None None None NoneRichmond

    28R Columbia/ Recycled 0.078 None None None None OpenSurfaceRichmond Texture

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    Figure2.In-SituMixProperties(Task1)

    Figure3.RecompactedMixProperties(Task1)6

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    Figure4.CreepModulusValues(Task1)

    Figure5.RecoveredAsphaltBinderProperties(Task1)

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    recoveredasphaltcementwascharacterizedbymeasuringtheComplexShearModulus(G*)and

    thePhaseAngle(*)oftheasphaltcement.G*istheratioofthemaximumshearstiffness(Tmax)tomaximumshearstrain(Ymax).Thetimelagbetweentheappliedstressandtheresultingstrainisthephaseangle*.

    AccordingtoSHRPspecifications,ruttingpotentialorthepermanentdeformationofthemixis

    controlledbylimitingtheruttingfactorG*/Sin*athightesttemperaturestovaluesgreaterthan2.2kPaafterRTFOT(rollingthinfilmoventest)aging.Forthisstudy,thespecificationtesttemperatureforthestateofGeorgiaforruttingwasassumedtobe64C(148F)sincetherecommendedSHRPpavinggradewhichsatisfiesrequirementsformostofthegeographicalareaofGeorgiaisPG64-22.Higherruttingfactorsat64C(148F),indicatebetterruttingresistance.

    Fatiguecrackingnormallyoccursatlowtomoderatetemperatures.AccordingtotheSHRP

    specifications,itiscontrolledbylimitingthefatiguecrackingfactorG*Sin*oftherecoveredasphaltbindertovalueslessthan5000kPaatthetesttemperature.ThetesttemperatureforfatiguecrackinginGeorgiawasassumedtobe22C(72F).ThefivepavementsectionsinTask1havebeeninservicefrom1to3years,averagingabouttwoyears.TherecoveredasphaltbinderisthereforeexpectedtobesofterthanthecorrespondingPressureAgingVessel(PAV)residuewhichsimulatesfivetotenyearsinservice.However,thefatiguefactorcanbeusedinthisstudyforcomparingthepotentialfatiguebehaviorofthecontrolandrecycledsections.Lowerfatiguecrackingfactorsindicatebetterabilityfortheasphaltbindertodissipatestresswithoutcracking.

    Figure5showsthevaluesofG*/Sin*andG*Sin*obtainedforthesefiveprojects.

    ANALYSISOFTESTDATA(TASK1)

    Apairedt-testisappropriateforanalyzingthetestdatainTask1todetermineifthereisa

    significantdifferencebetweenthetestvaluesobtainedinrecycledandcontrolsection.Task1consistsoffivepairs(projects),eachpairconsistingofonerecycledandonecontrolsection.Averagetestvalueswereusedintheanalysis.Table3givesthepairedt-testresults.

    VisualEvaluation

    TheextentofdistresswasquantifiedandisreportedinReference10.Nosignificantrutting,raveningandalligatorcrackinghasoccurredinanyofthesites(Table2).RuttingoccurswhentheHMAmixistoosoft.Alligator(fatigue)crackingcanoccuriftheHMAmixistoostifforbrittle.Theoverallpavementsurfaceevaluationandratingindicatesthatbothrec...

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