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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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