Performance of Recycled Hot Mix Asphalt Mixtures

Embed Size (px)

Text of Performance of Recycled Hot Mix Asphalt Mixtures

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

    1/19

    PERFORMANCEOFRECYCLEDHOTMIXASPHALTMIXTURES

    By

    PrithviS.Kandhal

    ShridharS.RaoDonaldE.WatsonBradYoung

    PaperpublishedinTransportationResearchBoard,TransportationResearchRecord1507,1995

    277TechnologyParkway Auburn,AL36830

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

    2/19

    PERFORMANCEOFRECYCLEDHOTMIXASPHALTMIXTURES

    By

    PrithviS.Kandhal

    AssistantDirectorNationalCenterforAsphaltTechnology

    AuburnUniversity,Alabama

    ShridharS.Rao

    GraduateStudentAuburnUniversity,Alabama

    DonaldE.Watson

    AssistantStateMaterialsandResearchEngineerGeorgiaDepartmentofTransportation

    BradYoung

    AssociateResearchEngineerGeorgiaDepartmentofTransportation

    PaperpublishedinTransportationResearchBoard,TransportationResearchRecord1507,1995

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

    3/19

    DISCLAIMER

    Thecontentsofthisreportreflecttheviewsoftheauthorswhoaresolelyresponsibleforthefactsandtheaccuracyofthedatapresentedherein.ThecontentsdonotnecessarilyreflecttheofficialviewsandpoliciesoftheNationalCenterforAsphaltTechnologyofAuburnUniversity.Thisreportdoesnotconstituteastandard,specification,orregulation.

    i

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

    4/19

    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

    ii

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

    5/19

    Kandhal,Rao,Watson,&Young

    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.

    1

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

    6/19

    Kandhal,Rao,Watson,&Young

    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

    2

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

    7/19

    Kandhal,Rao,Watson,&Young

    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

    3

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

    8/19

    Kandhal,Rao,Watson,&Young

    compacted.Airvoidcontentsofthecompactedspecimenswerealsoobtained.Confined,

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

    TheextractionoftheagedasphaltcementfromtheHMAmixtureswasaccomplishedbytheASTMD2172(MethodA)procedureusingtrichloroethylene.TheasphaltcementfromthesolutionwasrecoveredusingtheRotovaporapparatusasrecommendedbytheSHRPprogram.Therecoveredasphaltcementwastestedforviscosityat60C(