Chapter 2B
Designand Control of Stone Matrix Asphalt (SMA)Mixtures
1.General Scope
TheDepartment has established procedures forthe designandcontrol of Stone MatrixAsphalt(SMA). SMA is a hot-mixasphaltconsistingof twoparts, ; acoarse aggregate skeletonanda richasphaltbindermortar. Themortarisamixtureof asphaltbinder,mineralfiller and astabilizingadditive.SMA mixtures must have anaggregate skeleton with coarse aggregate-on-coarseaggregate contact, generallyreferred to as stone-on-stone contact. Much of thedesignandcontrol ofSMA is consistent withthe procedures for Superpave outlined inChapter2A, but therearesome differencesaswell.Thepurpose of these proceduresdiscussedinChapter 2Bis toprovideguidancefor thedesign and useof StoneMatrixAsphaltforDepartment work.
TheDepartment will follow theStone MatrixAsphalt mixdesignprocedure andspecificationscontained in theAASHTO R 46,StandardPractice for DesigningStone MatrixAsphalt (SMA)and the AASHTOM 325StandardSpecificationfor Stone MatrixAsphalt(SMA) except asrevisedherein. All AASHTOstandardpractices,specificationsand test proceduresareimpliedto reference the most currentapprovedand published versionavailableatthetimeofbid letting.
2.DepartmentRevisions to AASHTOR 46– StandardPractice forDesigning StoneMatrix Asphalt (SMA)
AASHTO R 46,Section 3. Terminology
ReviseSection 3 byaddinga newSubsection as follows:
3.8 DesignNumber of Gyrations(Ndes) – Thenumber of gyrationswhich, whenapplied to the design mixturespecimens, results in3.5 – 4.0 percent airvoids anddetermines the asphalt content.
AASHTO R 46,Section 4. Summary ofthePractice
ReviseSubsection 4.2 as follows:
Replace thefourth sentencewith “Whereno previous historyis available,it isrecommended thataninitialtrialasphalt binder content be selectedaccordingto TableC of Publication 408, Section 419.”
ReviseSubsection 4.3 as follows:
Delete Note2. Mixes must meet theminimum asphaltcontentrequirements of Table Cin Publication 408, Section 419.
Revise Subsection 4.4 completely as follows:
The moisture susceptibility of the design aggregate structure is evaluated at the design binder content: the mixture is conditioned according to the revised mixture conditioning for volumetric mixture design and production quality control testing time (Appendix I herein) plus an additional 2 hours, compacted to 6.0 +/- 1.0 percent air voids in accordance with T 312, and evaluated according to T 283. All mixtures shall include either a compatible, heat stable, amine-based liquid anti-strip, hydrated lime or another compatible alternate anti-strip additive. Incorporate the anti-strip additive at least at the minimum dosage rate published on the anti-strip additive’s technical data sheet from the anti-strip manufacturer (typically 0.25% by mass of asphalt).
Mixtures that incorporate both coarse and fine aggregates classified as a type of Sandstone, Siltstone, Slag, Quartz, Shale, or Gravel shall include either a compatible, heat stable, amine-based liquid anti-strip, hydrated lime or another compatible alternate anti-strip additive incorporated at a dosage rate one level higher than the minimum recommended dosage rate recommended by the manufacturer (typically 0.50% by mass of the total asphalt).
The producer may elect to perform additional testing for mixtures that incorporate both coarse and fine aggregates classified as a type of Sandstone, Siltstone, Slag, Quartz, Shale, or Gravel with an anti-strip agent dosage rate one level higher than the minimum dosage rate recommended by the manufacturer compared to the test results that incorporate anti-striping agent at the minimum dosage rate. If all of the following bullet points are true design the JMF with the higher dosage rate.
- The TSR of the higher dosage mixture is greater than the TSR of minimum dosage mixture.
- The conditioned and unconditioned tensile strength of all AASHTO T 283 tests are above the minimum tensile strength requirement in section 11.3
- The unconditioned tensile strength of the higher dosage mixture is higher than or within 10 psi below the unconditioned tensile strength of the lower dosage mixture.
The design shall meet the tensile strength ratio requirement of M 325..
ReviseSection 4 byadding a newSubsection as follows:
4.6Review of Job-MixFormula(JMF)– Thecontractorwill besolelyresponsible todesign amixthat meets all Departmentrequirements. The contractor shall submit therequired test results, the composition of the mixtureand thecombinedaggregategradationcurves proposed foruse in theproduction ofthe mixtureto the DistrictMaterialsManager/MaterialsEngineer (DMM/DME)forreview at least three weeksprior to the scheduled start of work. Submit mixdesigns to the DME/DMM forreviewfollowingthe proceduresoutlined in AppendixJ.Theacceptabilityof thebituminousconcrete producedfromanymixdesign is determined asspecified in Publication 408,Section 419 in addition to the criteriaspecified herein.
Whenever theContractor’s gradationsandcalculations do not check, the DMM/DMEwill request the Contractor to do additionaltestingand/orrecalculateandsubmit thecorrectmathematical solutions.TheDMM/DME mayrequest, at his option, to observetestingof thetrial mix. Hemayalso request thatmaterials be submitted to theMaterials and TestingDivision(MTD)for theevaluation of themix.TheDepartmentreserves the right to review anydesignthrough plant production,prior to usingforDepartment work, at no additional cost to the Department. SeeBulletin 27, Chapter 2Aand the revisions for AASHTOM 323, Section 7 forthe procedure on thestatisticalevaluation ofaJMFthrough plant production andreplace the references toPublication408, Section 409 with equivalentvaluesfrom Section 419.
AASHTO R 46,Section 6. Selection ofTrialGradations
ReviseSubsection 6.1as follows:
Replace both references to M 325 for gradationwith the gradationrangesasspecifiedin Table Bof Publication408, Section 419.
AASHTO R 46,Section 7. Selection ofTrialBinder Content
ReviseSubsection 7.1completely as follows:
Abindercontent shouldbe selectedaccordingtoTable Cof Publication 408, Section419.
AASHTO R 46,Section 9. Selection ofDesiredGradation
ReviseSubsection 9.1as follows:
Replace reference to AASHTOT 166 with PTM No. 715, typicalthroughout
AASHTO R 46,Section 10. Selection ofOptimumBinder Content
Revise Subsections 10.1 and 10.2 as follows:
Replace AASHTO M 325 criteriawith that outlined in Tables B and CofPublication408, Section 419.
AASHTOR46,Section11.MoistureSusceptibility
ReviseSection11byaddingaNoteas follows:
Note7-Ithasbeenshownthatthechemicalcompositionofasphaltbinders,aggregatesandanymixtureadditivescanhaveastronginfluenceontheresultsobtainedfromthesetestingprocedures. Therefore,itisrecommendedthatthesources ofmaterials(binderandadditives)usedinthedesignprocessbethesameasthematerialsthatwillbeincorporatedinthemixtureduringproduction. Ifeitherofthesecomponentschangeatthetimeofproduction,theactualproductionmixturemustbeverifiedbyretesting,initiallywithASTMD3625(BoilingWaterTest)asascreeningtest. Otherwise,thedesigntestingmaynotberepresentative.
Note7A-Allmoisturesusceptibilitysamplingandtesting shall bedirectlywitnessedanddocumentedbyPennDOTinspectionpersonnelunlessotherwiseapproved,inwriting,bytheDME/DMM.
ReviseSubsection11.1bycompletelydeletingexistinglanguageandreplacingwithlanguageas follows:
11.1Prepareeitherlaboratory-mixed, laboratory-compacted specimensorfieldmixed(plant-mixed),laboratory-compacted specimensaccordingtoAASHTOT283withmodificationsasfollows:
AASHTO T283,Section6.5,addthefollowing totheend:
Preparebatchescomposedof thedesignaggregatestructureatthedesignbindercontent.
AASHTOT283,Section6.5,revisethe'compactionmethodandairvoidsasfollows:
Compactthespecimensto6± 1.0percentairvoidsaccordingtoT312.
AASHTOT283,Section7.3,revise completely asfollows:
Field-mixed(plant-mixed)samplesareonlypermittedtobeobtainedfrom asphaltproductionplantsandevaluatedformoisturesusceptibilityprior toshipmenttoanyPennDOTfundedprojectlocation. ObtainalargeenoughsampleaccordingtoPTMNo.746tosplitthesampleandpreparetherequiredsixcompactedspecimens,totestthesampleaccordingtoPTMNo.757 orPTMNo.702andPTMNo.739,andtoperformtwotestsaccordingtoAASHTOT209asrequiredinAASHTOT283,Section9.1. Comparethegradationandasphaltcontentofthetestedmaterialtothemultiplesample(n2:3)tolerancesinPublication408,Section419,TableD.Ifanyoftheindividualsievesizegradationsorasphaltcontentareoutsideofthemultiplesample(n2:3)tolerancesinPublication408,Section419,TableD,thecompletesampleisinvalidandmustbediscarded.
AASHTOT283,Section7.4,revisethefirstthreesentences completelyasfollows:
Noloose-mixcuringasdescribedinSection6.4shallbeperformedonthefield-mixedsamples. Aftersampling,dividethesampletoobtainthedesiredsizeinaccordancewithR47.Next,placethemixtureinanovenfor
2h±10minatthe compactiontemperature±3°C(5°F)priortocompaction.
AASHTOT283,Section8,delete Section8initsentiretyincludingSections8.1, 8.2and8.3.
11.2Evaluateandgroup,precondition,test,andcalculatethetensilestrengthratioaccordingtoAASHTOT283withmodificationsasfollows.
AASHTOT283,Section 9.1Section 9.1,revisecompletelytoreadasfollows:
Aftercuringand/orheatingthemixturesamplestothecompactiontemperatureasdescribedinSections6.4and6.5orSection7.4,as
appropriate,determine thetheoreticalmaximumspecificgravity(Gmm)ofthosesamplesaccordingtoAASHTOT209asmodifiedbyBulletin27,AppendixIexceptthesampleconditioningrequiredforGmminBulletin27,AppendixIisnotrequired. DetermineGmmon aminimumoftwosamplesandaveragetheresultsforcalculatingpercentairvoidsofthespecimens.
AASHTOT283,Section 9.4,revisefirstsentencecompletelyasfollows:
Determinethebulkspecificgravity(Gmb)ofeachspecimenaccordingtoPTMNo.715.
AASHTOT283,Section9.5,revisecompletelytoreadasfollows:
Calculatethepercentageofairvoids(Pa)inaccordancewithT269usingthebulkspecificgravity(Gmb)andthetheoreticalmaximumspecific gravity(Gmm)asdeterminedintherevisedAASHTOT283Sections 9.4and9.1
AASHTOT283,Section10.3.l,addnewNote5andTableasfollows:
Note5-Thefollowingtableisprovidedtohelpwithunderstandingvacuumpressurereadingsandunderstandingweakerandstrongervacuum.
UnderstandingVacuumGaugePressureReadingsVacuumGauge Type / UnitofMeasure / VacuumReadingwithNoVacuumApplied / VacuumReadingwithWeakestVacuumApplied / Vacuum ReadingwithStrongestVacuum Applied
Partial/Relative / InchesofMercury(Hg) / 0(Zero) / 10in.Hg / 26in.Hg
Partial/Relative / mmofMercury(Hg) / 0(Zero) / 254 mmHg / 660mmHg
Absolute / InchesofMercury(Hg) / Approx.29.9in.Hg / 19.9in.Hg / 3.9in.Hg
Absolute / mmofMercury(Hg) / Approx.760mmHg / 506mmHg / 97.5mmHg
AASHTOT283,Section10.3.2.revisecompletelytoreadasfollows:
Determinethemassofthesaturated,surface-dryspecimenafterpartialvacuumsaturation(B')byPTMNo.715.
AASHTOT283,Section12.l,addnewSubsection12.1.1asfollows:
12.1.1Calculatetheaverage( x( )x)andstandarddeviation(s)oftensilestrengthsforboththedrygroupofspecimensandthefreeze-thawgroup.CalculatetheCoefficientofVariation(C.V.)foreachgroupbydividingthestandarddeviationbytheaverage:
x
(%)
%
IftheC.V.isgreaterthan12%forthedrygroup,or24%forthefreeze-thawgroup,thetestresultsshouldbeviewedassuspectandanewsubsetofspecimenspreparedandtested.
IfonlyoneoftheresultsissuspectandanalysisaccordingtoPTMNo.4identifiesthatresultasanoutlier,areplacementisinitiallyonlyrequiredforthatspecimen.IftheC.V.consideringthereplacementspecimeninplaceoftheoutlierisstillgreaterthantheacceptablelimit,prepareandtestanentiresubsetofnewspecimens. Eachgroupofspecimens,dryorfreeze-thaw,is definedasasubset.
11.3If theaveragedrystrengthislessthan80 psi(552kPa)ortheaveragewet/freezestrengthislessthan50psi(345kPa),themixisunacceptable. Moisture susceptibility testing must be reevaluated, at a minimum, once every five years, if mixture components, sources, and JMF targets remain the same, to account for variations in aggregate sources and other mix components. When component material sources change or component material proportions or JMF targets significantly change, as determined by the DME/DMM, moisture susceptibility must be reevaluated.
If any JMF fails to meet any of the requirements above or in AASHTO T 283, any retest or testing of JMF versions of the same aggregate combination (outlined in note 17B above) must be approved by the DME/DMM.
Compute the dosage rate of liquid anti-stripping agent as follows:
- Compute the anti-strip dosage rate based on the total asphalt in the mixture.
For WMA mixture produced by a WMA Technology categorized as a foaming additive or process (e.g., foaming additive or mechanical foaming), if the HMA version of the JMF requires an anti-strip additive to meet the moisture susceptibility requirements, the WMA version of that JMF is required to contain the same minimum amount of anti strip additive required in the HMA version of the JMF.
If the Producer elects to use an alternate anti-strip additive that is not a typical amine-based anti-strip additive, contact the DME/DMM at least three weeks prior to start of work. If directed by the DME/DMM, perform moisture sensitivity analysis with the alternate anti-strip additive incorporated at the alternate anti-strip manufacturer’s recommended dosage rate. Demonstrate, by the moisture sensitivity test results that the alternate anti-strip additive meets the specified moisture sensitivity requirements. If directed by the DME/DMM, provide written documentation (e.g., research or project evaluation reports) from the manufacturer of the alternate anti-strip additive showing successful use of the alternate anti-strip additive in asphalt mixtures at the same dosage rate as is being recommended for the JMF.
11.4Thedesignshallmeetthetensilestrengthratio(TSR)requirementlistedin
11.4 AASHTOM325,Section9.3
11.5If visualstrippingoftheasphaltfilmisobservedfromtheT283specimensandestimatedtobe5%orgreaterofthespecimenfacearea,furtherevaluatemoisturesusceptibilitybyperformingtestprocedureASTMD3625(BoilingWaterTest).(Uncoatedareasduetofracturedaggregateshouldnotberecordedasstripped). Whenasphaltbindercoatingislessthan95%,asdeterminedbyASTMD3625,retestthemixtureaccordingtoAASHTOT 283asoutlinedabove. Allcollectedspecimensandtestdatashouldbecarefullyreviewedpriortodeterminingacceptability. Ifthereisanydoubtconcerningthemixture'ssusceptibility,therecommendedapproachistoconsiderthemixmoisturesusceptible.
11.6If theDME/DMMdeterminesthatthemoisturesusceptibilityresultsaresuspectorinconsistentwithhistoricaldataorfieldperformanceaspecifiedlevelofanti-stripmayberequiredinamixtureatnoadditionalcosttotheDepartmentpriortoapproval.
11.7Moisturesusceptibilitytestingmustbererun,ataminimum,onceevery5yearstoaccountforvariationsinaggregatesourcesandothermix components.