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MIX DESIGN FOR HMA ECYCLING - Purdue Engineering · PDF fileOutline current practice with RAP...

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  • MIX DESIGNFOR HMARECYCLINGRebeccaMcDanielNorthCentralSuperpaveCenter

    PavementPerformancePredictionSymposium2008Laramie,WyomingJuly16,2008

  • PRESENTATION OUTLINEOutlinecurrentpracticewithRAPmixdesignandhowwegottothispoint

    Laygroundworkforotherpresentationsshowingpossiblerefinementsandotherconsiderations

  • POSSIBLE EFFECTS OF RAPAtlowRAPcontents,theremaybelittleagedbindertoaffectpropertiesofblendAthigherRAPcontents,thehardenedRAPbindermaystiffenthemix

    Goodforrutting,notsogoodforcracking

    TheaggregateintheRAPmayaffectstructureandstabilityofthemixMixdesignshouldconsider/accountforthesepossibleeffects

  • RAPMIX DESIGN BASICSAggregateConsiderationsIncludeRAPaggregateindeterminationsof:

    SpecificgravityGradationFineaggregateangularityCoarseaggregateangularityFlatandelongatedcontent

    RAPSpecificGravityUseRAPagg effectivespecificgravity,orBackcalculate bulks.g.fromRicedensityandassumedabsorption

  • RAPMIX DESIGN BASICSBinderConsiderationsReduceaddedbindertoaccountforRAPbinder

    ForhigherRAPcontents,usesoftervirginbindergradetoblendwithandsoftenthehardenedRAPbinder

    Costandconstruction(compaction)implications

  • CURRENT TIERS

    Upto15%RAP,nochangeinbindergrade.

    1625%RAP,lowerbindergradebyoneincrement.

    Morethan25%,createblendingcharts.AssumeslinearblendingExtract,recoverandtestRAPbinderHigh,lowandintermediatetemperaturesDSR(orig,RTFO,PAV),BBR(Sandm)

  • HIGH TEMPERATURE BLENDING CHART,KNOWN RAPCONTENT

    52586470768288

    0% 20% 40% 60% 80% 100%

    Percentage of RAP

    Tcr

    itica

    l, C

    54.3

  • LOW TEMPERATURE BLENDING CHART,KNOWN VIRGIN BINDER

    -24

    -18

    -12

    -6

    0

    0% 20% 40% 60% 80% 100%

    Percentage of RAP

    Tcr

    itica

    l, C

  • NCHRP912,IncorporationofReclaimedAsphaltPavementintheSuperpaveSystem

    NCSCandtheAsphaltInstituteRAPfromConnecticut,FloridaandArizonaCompleted2000,published2001ChangesinthreeAASHTOstandards

    Regionalstudy,UseofReclaimedAsphaltPavementUnderSuperpaveSpecifications

    RAPfromIndiana,Missouri,MichiganCompleted2003

    SO,HOW DID WE GET HERE?

  • ISSUES ADDRESSEDInNCHRP912

    IsRAPablackrock?EffectsofRAPonbindergradeEffectsofRAPonmixtureproperties

    InRegionalstudyDoNCHRP912findingsapply?Canyouuse40to50%RAPinaSuperpavemix?Islinearblendingappropriate?Comparedplantproducedmixstiffnesstoblendingchartstiffness

  • MAJOR FINDINGS OF NCHRP912

    RAPisnotablackrockBut,atlowRAPcontents,thereisnotenoughRAPtochangebinderormixpropertiesAsRAPcontentincreases,effectsbecomeappreciableSheartesting,beamfatigueandlowtemperaturetestingshowedsimilarstiffening.

    Important mustaccountforthistoavoidincreasedcracking(usesoftervirginbinder)

    Linearblendingchartsvalid

  • REGIONAL STUDYLargelyconfirmedNCHRPfindingsCandesignSuperpavemixeswith4050%RAP

    AggregategradationintheRAPmaylimithowmuchyoucanuse

    LinearblendingchartsgenerallyappropriateLabandplantproducedmixesagreeprettywell

  • FREQUENCY SWEEP MO

  • DOES LINEAR BLENDING WORK?

    Michigan

    0102030405060708090

    0 20 40 60 80 100RAP Content (%)

    Crit

    ical

    Tem

    pera

    ture

    , C

    OriginalRtfoRtfo-Pav

    Plant Mix

  • STILL NOT CONVINCED?

    Missouri

    0102030405060708090

    0 20 40 60 80 100RAP Content (%)

    Crit

    ical

    Tem

    pera

    ture

    , C

    OriginalRtfoRtfo-Pav

    Plant Mix

  • Indiana

    0102030405060708090

    0 20 40 60 80 100RAP Content (%)

    Crit

    ical

    Tem

    pera

    ture

    (o C

    )

    OriginalRtfoRtfo-Pav

    Not linear but stiffer than expected.

    LINEAR BLENDING IS NOT PERFECT

  • ESTIMATED VS.MEASURED

    Aging IN MI MO

    Orig -6.2 -6.6 -7.8

    RTFO -3.2 -0.4 -0.4

    PAV -3.5 0.5 0.7

    Estimated - Measured

  • INDIANA ANOMALY?ConsistentpatterninbinderandmixNotobservedinMI,MOor912mixesPlantmayhavestiffenedbindermorethanexpectedMaterialswereoneyearolderthanMIandMO

  • AFTERMATH OF PREVIOUS STUDIESRAPuseincreasedafterAASHTOstandardswereissuedMostMidwesternstatesreportRAPuseisbacktowhereitwaspreSuperpave

    HigherinplaceslikeMissouri

    ExperienceswithRAPgenerallyverygoodliketheywerepreSuperpave

    ManycontractorspreferRAPmixesLinearblendingworksfrequently butnotalways

  • LIMITATIONSOnlythreeRAPsourcesevaluatedineachstudy

    RAPfractionationnotconsidered notcommonatthetime

    Newer,bettertestsnotyetcommon

    Experienceandresearchshowtherecommendationsmaybetoosimple

  • CURRENT RAPRESEARCH NCSC

    LowTemperaturePerformancePropertiesofHotMixAsphaltContainingRAP

    SocalledPlantMixStudyEvaluatedplantproducedmixeswithupto40%RAPandtwovirginbindergradesOriginallyproposedtofocusoneffectsofRAPonlowtemperaturepropertiesExpandedtootherpropertiesandmorematerials.FHWAfunded

  • WHAT WE DID

    MilestoneContractorsLLCproducedsixmixesthroughoneplantovertwodaysHeritageResearchGroupandNCSCtestedRAP,virginandmixtureproperties

    Binderproperties PGbindertestsMixproperties IndirectTensileStrength,DynamicModulus,ShearModulus

  • EXPERIMENTAL DESIGN

    Reclaimed Asphalt Pavement

    Binder Grade 0% 15% 25% 40%

    PG 58-28 X X

    PG 64-22 X X X X

  • WHAT DID WE SEE?

  • CRITICAL CRACKING TEMPERATURESMix RAP Content Tc (C)

    A PG64-22 0 -28.9

    B PG64-22 15 -23.3

    C PG64-22 25 -25.6

    D PG64-22 40 -22.8

    E PG58-28 25 -27.2

    F PG58-28 40 -23.9

  • PG64-22, 15% RAP

  • PG64-22, 40% RAP

  • PG58-28, 40% RAP

  • PHYSICALLY BLENDED BINDERS

  • WHAT DOES THIS SUGGEST?Forthesematerialsandthisplant,theRAPdidnothaveasmuchimpactasexpectedThehigherRAPcontentswere,ingeneral,notsignificantlystifferthanvirginmixThebinderdidnotstiffenlinearlywithincreasingRAPcontentInthiscase,droppingthevirgingradetoPG5828for25%RAPwasnotnecessaryWhy?Compatibilityproblem?

  • IS THIS CONCLUSIVE?Certainlynot!

    Onlyoneplant,oneRAPsource,onesetofvirginmaterialsMaybeexceptionratherthanruleWeneedtotestmorematerialsfrommoreplantstounderstandtrueeffectsFourmorecontractorshavereplicatedtheplantmixexperimentTestingisinprogressWewillalsoinvestigateeffectofextraction/recoverymethod

  • WHAT THIS SUGGESTSBut,itdoessuggestthatthereismorethatweneedtounderstandaboutRAP,itseffectsanditscompatibilitywithvirginmaterialsplusplantoperationsMaybecurrentbindergraderecommendationsaretoorestrictive toosimplified

  • CURRENT STATE OF KNOWLEDGEWithmanymaterialsandplants,complete(ornearlycomplete)blendingdoesoccur.Inothercases especiallywithveryhardbinders(shingles),highRAPcontentsor??? completeblendingmaynotoccur.

    Temperature,Time,Compatibility,PlantColloideffect?

    ThereismuchwestilldonotunderstandaboutRAP

  • MORE INFO:

    RebeccaS.McDanielTechnicalDirectorNorthCentralSuperpaveCenter765/[email protected]://engineering.purdue.edu/NCSC/

    mailto:[email protected]

    Mix Design for HMA RecyclingPresentation OutlinePossible Effects of RAPRAP Mix Design BasicsRAP Mix Design BasicsCurrent TiersHigh Temperature Blending Chart, Known RAP ContentLow Temperature Blending Chart, Known Virgin BinderSo, How Did We Get Here?Issues AddressedMajor Findings of NCHRP 9-12Regional StudyFrequency Sweep - MODoes Linear Blending Work?Still not convinced?Linear Blending is not PerfectEstimated vs. MeasuredIndiana Anomaly?Aftermath of Previous StudiesLimitationsCurrent RAP Research - NCSCWhat We DidExperimental DesignWhat did we see?Critical Cracking TemperaturesSlide Number 26Slide Number 27Slide Number 28Physically Blended BindersWhat does this suggest?Is this conclusive?What this suggestsCurrent State of KnowledgeMore info:

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