Lesson-4-Hot-Mix-Asphalt

Lesson4:HotMixAsphalt–MixDesignCEE595ConstructionMaterialsWinter2019Reading•VirtualSuperpaveLaboratory•WSDOTPavementGuideInteractiveSectionSubsectionAggregateTestsGradation&SizeMixDesignAllModuleSectionMixDesignHveemMethodMixDesignMarshallMethodLessonOutline1.Hotmixasphalt(HMA)description2.SuperpavemixturedesignprocedureHotMixAsphalt(HMA)•Bituminousconcrete•Distinguishedby:–Materials(asphaltbinderandaggregate)–Mixdesignmethods–Elevatedmixingtemperature•Othernames:–Asphaltconcrete(AC)–Blacktop–BitumenSection1HMAbytheNumbersItemU.S.EuropeJapanAnnualProductioninmillionsoftons500–600300–33075–82Percentagerecycled80%0–80%50%ProductionCompanies110025001000ProductionPlants360047001500EuropeandJapannumbersfromtheEuropeanAsphaltPavementAssociation(eapa.org)Section1HMAConstituentsSection1TypesofHMASection1HotMixAsphalt•Describedby:–Maximumaggregatesize–Aggregategradation–Asphaltbinder–AsphaltbindercontentSection1MaximumAggregateSize•Largestaggregate“diameter”asdefinedby:–MaximumSizeThesmallestsievethroughwhich100percentoftheaggregatesampleparticlespass–NominalMaximumSizeThelargestsievethatretainssomeoftheaggregateparticlesbutgenerallynotmorethan10percentbyweightSection1Section1Gradation•Densegraded–Mostcommon•Gapgraded–Stonematrixasphalt(SMA)•Opengraded–Usedasasurfacecourseinmanyareas•Uniformlygraded–NotusedasaconstructionmaterialSection1Section1AsphaltBinder•Chooseasphaltbindergrade–Selectagradebasedon:•Designpavementhightemperature•Designpavementlowtemperature–Adjustbasedonreliability–Adjustbasedontrafficspeed&loading•AddmodifierstoachievecertainpropertiesSection1AsphaltBinderContent•Ratioofasphaltbindertoaggregate•Determiningthisisakeycomponentofmixdesign•Typicalbindercontents–Usuallyexpressedasapercentagebyweightoftotalmixture–DensegradedHMA=4.5to6.0percent–SMA=6.0–8.0percentSection1SuperpaveMixDesignProcedureSection2Concepts•Wedesignvolumebutmeasuremass•Specificgravityisveryimportant–ConvertsmasstovolumeConstituentTypicalValuesByTotalVolumeByTotalMixWeightAir4%0%Asphalt10%5%Aggregate86%95%Section2Variables•Aggregate•Asphaltbinder•RatioofaggregatetoasphaltbinderSection2Goals•Stability(deformationresistance)•Durability•Fatigueresistance•Ductility(lowtemp.crackingresistance)•Moisturedamageresistance•Skidresistance•WorkabilitySection2BasicProcedure•Selectaggregate•Selectasphaltbinder•Designaggregatestructure•Selectasphaltbindercontent•Conductperformancetests•Developjobmixformula(JMF)Section2SelectAggregate•Mustmeet:–Consensusrequirements–SourcepropertiesSection2SelectAsphaltBinder•Almostalwaysdonetolocalstandard–EliminatesthecalculationsassociatedwithLTPPBindsoftware–Easiertofollowinspecifications–EasierforsuppliersDesignAggregateStructure•Notmanyformalprocedurestodothis•TypicalSuperpaveaggregatestructurescreatequarrywasteSelectAsphaltBinderContent•LevelofsamplecompactioniscriticalBleedingRavelingConductPerformanceTests•TherearenoneforSuperpaverightnow•Agenciestypicallyuse–Moisturesusceptibilitytest–Laboratorywheeltrackingdevices–HveemstabilometerImportantVolumetricProperties•Testsrunoncompactedsamples–Mixturespecificgravity(Gmb)–Aggregatespecificgravity(givesGsb,Gsa,Gse)•Testrunonloosemix(uncompacted)–Theoreticalmaximumspecificgravity(Gmm)–Oftencalled“Theoreticalmaximumdensity”–Oftencalled“Ricedensity”•Calculatedvolumes(basedonabovetests)–Airvoids(Va)–Voidsinthemineralaggregate(VMA)–Voidsfilledwithasphalt(VFA)Equations•Airvoids•VMA•VFA100mmmbmmaGGGV10011sbbmbGPGVMAsbsmbGPGVMA100VMAVVMAVFAa100TVaVVVPb=%asphaltbinderbyweightofmix,Ps=%aggregatebyweightofmixGsb=aggregatespecificgravityMixDesignDevelopJobMixFormula(JMF)•Endresultofmixturedesign•Aspecification(alongwithtolerances)usedforplantproductionofHMA•CannotbesignificantlyalteredwithoutanothermixdesignJobMixFormula(JMF)MixDesignOtherMixDesignMethods•MarshallMethod•HveemMethod•AllusethesamebasicprocedureSection2MarshallHammer•CompactssamplesinMarshallmethod–AnalogoustoSuperpavegyratorycompactorCaliforniaKneadingCompactor•CompactssamplesinHveemmethod–AnalogoustoSuperpavegyratorycompactorMarshallStabilityTest•SqueezessamplediametricallyMixDesignCompactedSamplesHeight2.5inchesDiameter4inchesMarshall&HveemSuperpaveHeight4.5inchesDiameter6inchesStudyQuestions•DrawavolumetricdiagramofHMAandlabelthefollowingvolumes:asphaltbinder,air,VMA,effectiveasphaltbinder,absorbedasphaltbinderandaggregate.•DiscussthethreemaintypesofHMA(inregardstotheirgradation)andwheneachmightbeappropriateforuse.•Whatisthedifferencebetween“maximumaggregatesize”and“nominalmaximumaggregatesize”?•Explainwhata0.45powercurveisandwhyitisusedforviewingHMAgradation.•Whyarethespecificgravitycalculationssoimportantinmixdesign?•Describethebasicmixdesignprocessincludingeachstep,howitisdone,whyitisdoneandanyspecialconsiderations.•WhatarethedifferencesbetweenSuperpave,MarshallandHveemmixdesignprocedures?DiscussionForumTheSGChasanissuewithinternalangleofgyration(seeSGC–Background).Basically,it’sadimensionthatisnotspecifiedininstrumentmanufacturebecauseitisassumedtobedirectlyrel