Lesson4HotMixAsphaltndash;MixDesign教训4热拌沥青混合料配合比设计.pptx

Lesson 4:Hot Mix Asphalt Mix DesignCEE 595 Construction MaterialsWinter 2008ReadingVirtual Superpave LaboratoryWSDOT Pavement Guide InteractiveSectionSubsectionAggregate TestsGradation&SizeMix DesignAllModuleSectionMix DesignHveem MethodMix DesignMarshall MethodLesson Outline1.Hot mix asphalt(HMA)description2.Superpave mixture design procedureHot Mix Asphalt(HMA)Bituminous concreteDistinguished by:Materials(asphalt binder and aggregate)Mix design methodsElevated mixing temperatureOther names:Asphalt concrete(AC)BlacktopBitumenSection 1HMA by the NumbersItemU.S.EuropeJapanAnnual Production in millions of tons500 600300 33075 82Percentage recycled80%0 80%50%Production Companies110025001000Production Plants360047001500Europe and Japan numbers from the European Asphalt Pavement Association(http:/www.eapa.org)Section 1HMA ConstituentsSection 1Types of HMASection 1Hot Mix AsphaltDescribed by:Maximum aggregate sizeAggregate gradationAsphalt binderAsphalt binder contentSection 1Maximum Aggregate SizeLargest aggregate“diameter”as defined by:Maximum SizeThe smallest sieve through which 100 percent of the aggregate sample particles passNominal Maximum SizeThe largest sieve that retains some of the aggregate particles but generally not more than 10 percent by weightSection 1Section 1GradationDense gradedMost commonGap gradedStone matrix asphalt(SMA)Open gradedUsed as a surface course in many areasUniformly gradedNot used as a construction materialSection 1Section 1Asphalt BinderChoose asphalt binder gradeSelect a grade based on:Design pavement high temperatureDesign pavement low temperatureAdjust based on reliabilityAdjust based on traffic speed&loadingAdd modifiers to achieve certain propertiesSection 1Asphalt Binder ContentRatio of asphalt binder to aggregateDetermining this is a key component of mix design Typical binder contentsUsually expressed as a percentage by weight of total mixtureDense graded HMA=4.5 to 6.0 percentSMA=6.0 8.0 percentSection 1Superpave Mix DesignProcedureSection 2Concepts We design volume but measure massSpecific gravity is very importantConverts mass to volumeConstituentTypical ValuesBy Total VolumeBy Total Mix WeightAir4%0%Asphalt10%5%Aggregate86%95%Section 2VariablesAggregateAsphalt binderRatio of aggregate to asphalt binderSection 2GoalsStability(deformation resistance)Durability Fatigue resistanceDuctility(low temp.cracking resistance)Moisture damage resistanceSkid resistanceWorkabilitySection 2Basic ProcedureSelect aggregate Select asphalt binderDesign aggregate structureSelect asphalt binder contentConduct performance testsDevelop job mix formula(JMF)Section 2Select AggregateMust meet:Consensus requirementsSource propertiesSection 2Select Asphalt BinderAlmost always done to local standardEliminates the calculations associated with LTPP Bind softwareEasier to follow in specificationsEasier for suppliersDesign Aggregate StructureNot many formal procedures to do thisTypical Superpave aggregate structures create quarry wasteSelect Asphalt Binder ContentLevel of sample compaction is criticalBleedingRavelingConduct Performance TestsThere are none for Superpave right nowAgencies typically useMoisture susceptibility testLaboratory wheel tracking devicesHveem stabilometerImportant Volumetric PropertiesTests run on compacted samplesMixture specific gravity(Gmb)Aggregate specific gravity(gives Gsb,Gsa,Gse)Test run on loose mix(uncompacted)Theoretical maximum specific gravity(Gmm)Often called“Theoretical maximum density”Often called“Rice density”Calculated volumes(based on above tests)Air voids(Va)Voids in the mineral aggregate(VMA)Voids filled with asphalt(VFA)EquationsAir voidsVMAVFAPb=%asphalt binder by weight of mix,Ps=%aggregate by weight of mix Gsb=aggregate specific gravityMix DesignDevelop Job Mix Formula(JMF)End result of mixture designA specification(along with tolerances)used for plant production of HMACannot be significantly altered without another mix designJob Mix Formula(JMF)Mix DesignOther Mix Design MethodsMarshall MethodHveem MethodAll use the same basic procedureSection 2Marshall HammerCompacts samples in Marshall methodAnalogous to Superpave gyratory compactorCalifornia Kneading CompactorCompacts samples in Hveem methodAnalogous to Superpave gyratory compactorMarshall Stability TestSqueezes sample diametricallyMix DesignCompacted SamplesHeight2.5 inchesDiameter4 inchesMarshall&HveemSuperpaveHeight4.5 inchesDiameter6 inchesStudy QuestionsDraw a volumetric diagram of HMA and label the following volumes:asphalt binder,air,VMA,effective asphalt binder,absorbed asphalt binder and aggregate.Discuss the three main types of HMA(in regards to their gradation)and when each might be appropriate for use.What is the difference between“maximum aggregate size”and“nominal maximum aggregate size”?Explain what a 0.45 power curve is and why it is used for viewing HMA gradation.Why are the specific gravity calculations so important in mix design?Describe the basic mix design process including each step,how it is done,why it is done and any special considerations.What are the differences between Superpave,Marshall and Hveem mix design procedures?Discussion ForumThe SGC has an issue with internal angle of gyration(see SGC Background).Basically,its a dimension that is not specified in instrument manufacture because it is assumed to be directly related to another specified dimension.Since this internal angle of gyration can vary between brands of SGCs and even between SGCs of the same brand,the industry is noticing that calculated bulk specific gravity(and thus the calculated air voids)of the same mixture can vary between SGCs even though the same number of gyrations is specified.Given that measurements of laboratory bulk density are often used by owners for acceptance testing and by contractors for process control,how does one reconcile this problem so that an SGC can be used for quality assurance testing(in other words,if each machine measures differently,how can the owner and contractor compare numbers)?For instance,a contractors machine may produce samples that indicate 4%air voids,while the agencys machine may indicate 6%air voids,while a third party machine may indicate 5%air voids all on the same mix.ReferencesEuropean Asphalt Pavement Association website.http:/www.eapa.orgMuench,S.T.et al.(2005).Virtual Superpave Laboratory.http:/guides.ce.washington.edu/UW/VSL/Muench,S.T.;Mahoney,J.P.and Pierce,L.M.(2003).WSDOT Pavement Guide Interactive.http:/guides.ce.washington.edu/UW/WSDOT Roberts,F.L.;Kandhal,P.S.;Brown,E.R.;Lee,D.Y.and Kennedy,T.W.(1996).Hot Mix Asphalt Materials,Mixture Design,and Construction.National Asphalt Pavement Association Education Foundation.Lanham,MD.