waste materials in hot mix asphalt: an overview

8/9/2019 Waste Materials in Hot Mix Asphalt: An Overview

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WASTEMATERIALSINHOTMIX ASPHALT-ANOVERVIEWBy

PrithviS.Kandhal

PaperpublishedinASTM,SpecialTechnicalPublication1193,1993

277TechnologyParkway Auburn,AL36830


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WASTEMATERIALSINHOTMIXASPHALT-ANOVERVIEW

By

PrithviS.KandhalAssistantDirector

NationalCenterforAsphaltTechnologyAuburnUniversity,Alabama

PaperpublishedinASTM,SpecialTechnicalPublication1193,1993


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DISCLAIMER

Thecontentsofthisreportreflecttheviewsoftheauthorswhoaresolelyresponsibleforthefactsandtheaccuracyofthedatapresentedherein.ThecontentsdonotnecessarilyreflecttheofficialviewsandpoliciesoftheNationalCenterforAsphaltTechnologyofAuburnUniversity.Thisreportdoesnotconstituteastandard,specification,orregulation.

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ABSTRACT

Numerouswastematerialsresultfrommanufacturingoperations,serviceindustries,sewagetreatmentplants,householdsandmining.Legislationhasbeenenactedbyseveralstatesinrecentyearstoeithermandatetheuseofsomewastematerialsortoexaminethefeasibilityofsuchusage.Thehotmixasphalt(HMA)industryhasbeenpressuredinrecentyearstoincorporateawidevarietyofwastematerialsintoHMApavements.Thishasraisedthefollowinglegitimateconcerns:(a)engineeringconcernssuchaseffectontheengineeringproperties(forexample,strengthanddurability),impactonproduction,andfuturerecyclability;(b)environmentalconcernssuchasemissions,fumes,odor,leaching,andhandlingandprocessingprocedures;and(c)economicconcernssuchaslifecyclecosts,salvagevalue,andlackofmonetaryincentives.

Thewastematerialscanbroadlybecategorizedasfollows:(a)industrialwastessuchascellulose

wastes,woodlignins,bottomashandflyash;(b)municipal/domesticwastessuchasincineratorresidue,scraprubber,wasteglassandroofingshingles;and(c)miningwastessuchascoalmine

refuse.AgeneraloverviewofprecedingwastematerialsincludingtheresearchworkdoneinthepastandtheirpotentialforuseinHMApavementsisgiveninthispaper.

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WASTEMATERIALSINHOTMIXASPHALT-ANOVERVIEW

PrithviS.Kandhal

Numerouswastematerialsresultfromeveryaspectofsocietyincludingmanufacturing,serviceindustries,sewagetreatmentplants,householdsandmining.Thedisposalofwasteproductsisprimarilydoneasfollows:

(a)Landfills

(b)Incineration,and(c)Recyclinginotherproducts

However,problemsarebeingexperiencedbecauseoftheinsufficientcapacityoflandfills,air

pollutionassociatedwithincinerators,andlimitedalternativesforrecycling.Legislationhasbeenenactedbyseveralstatesinrecentyearstoeithermandatetheuseofsomewastematerials

ortoexaminethefeasibilityofsuchusage.About450millionmegagrams(Mg)ofhotmixasphalt(HMA)areproducedintheUnitedStatesatacostofabout$12billion.TheHMAindustryhasbeenpressuredinrecentyearstoincorporateawidevarietyofwastematerialsintoHMApavements.Thishasraisedthefollowinglegitimateconcerns( 1).

ENGINEERINGCONCERNS

Thefollowingconcernsmustbeaddressedfromtheengineeringviewpoint.

PropertiesofHMA

Sincethewastematerialwillreplaceand/ormodifythepropertiesofasphaltcementbinderand/orHMA,itwillaffecttheengineeringproperties(suchasstrengthanddurability).

Therefore,theHMAcontainingthewastematerialmustbereevaluatedthoroughlyandcarefullybothinthelaboratoryandthefield.

ImpactonProduction

SomewastematerialsrequireachangeintheHMAproductionequipmentand/orprocessesand,therefore,theproductionislikelytobeaffected.

FutureRecyclability

ItisnotknowninmanyinstanceswhethertheHMAcontainingawastematerialcanbeeffectivelyrecycledinthefuturewithoutanyproblems.Forexample,HMAcontainingsignificantamountsofgroundtirerubberhasnotbeenrecycledasyet.Suchrecyclingmaypose

airpollutionproblems.

ConsistentQuality

Thewastematerialmayvaryinquality(chemicalorphysicalproperties)and,thus,affecttheengineeringpropertiesanddurabilityofthehotmixasphalt.

ENVIRONMENTALCONCERNS

Thefollowingconcernsmustbedealtwithfromanenvironmentalviewpoint,especiallywhenverytightemissionandenvironmentalcontrolsarealreadyinplaceonHMAproductionfacilities.

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Emissions/Fumes/Odor

Itisquitelikelythatsomewastematerialswillhaveemissions/fumes/odorproblemsbecauseHMAisproducedathightemperatures.Theseproblemsmightalsobefacedwhenrecycling

HMAcontainingthewastematerialinthefuture.

Leaching

Component(s)ofwastematerialsmaybesusceptibletoleachingfromHMApavementsandthuscausestormwaterand/orgroundwaterpollution.

HandlingandProcessingProcedure

Theseproceduresarenotfullydevelopedforallwastematerials.SomewastematerialscouldbehazardousandcouldposehealthrelatedriskstoworkersintheHMAindustry.

ECONOMICCONCERNS

Fromaneconomicviewpoint,thefollowingconcernsmustalsobeaddressed.

Price

MandateduseofwastematerialsislikelytoraisethepriceofHMA.Forexample,virginaggregatesaregenerallyavailablelocallyatlowercostscomparedtowastematerialssuchaswasteglasswhichmustbehauled.

LifeCycleCosts

LifecyclecostsneedtobedeterminedforHMApavementscontainingwastematerials.Itis

quitepossiblethatthewastematerialmaynotaffecttheinitialengineeringpropertiesoftheHMApavementbutreduceitsservicelife.

DisposalCosts

IftheHMAcontainingthewastematerialscannotberecycled,thenitsdisposalcostsneedtobedetermined.

SalvageValue

SalvagevaluesofHMAcontainingthewastematerialsarenotknown.

LackofIncentive

AtthepresenttimethereisalackofmonetaryincentivestousethewastematerialsinHMA.

CATEGORIZATIONOFWASTEMATERIALS

Thewastematerialscanbroadlybecategorizedasfollows( 2).SomewastematerialswhichhavebeenusedexperimentallyorroutinelyinHMAarealsogivenforeachcategory.

(a)IndustrialWastes

CelluloseWastesWoodLigninsBottomAsh

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FlyAsh(b)Municipal/DomesticWastes

IncineratorResidueSewageSludgeScrapRubberWasteGlassRoofingShingles

(c)MiningWasteCoalMineRefuse

By-productsfromindustrialprocesses,suchasblastfurnaceslags,steelslagsandsulphurwere

consideredwastematerialsatonetime.However,theseproductsarenowgenerallyusedonaroutinebasisand,therefore,willnotbediscussed.AdetaileddiscussionofsomeselectedwastematerialsusedinHMAfollows.

CELLULOSEWASTES

Cellulosewastesincludeagriculturalwastes(cropresidues,forestingwastes),manufacturingwastes(foodprocessing,woodandpaperindustry),andurbanrefuse(municipalsolidwaste,manufacturingplanttrash).Apyrolysisprocesshasbeenusedoconvertcellulosicwastetoabinder(3).However,theresultingbinderwasnotsuitablefordirectuseasasubstituteforasphaltcementbecauseitstheologicalpropertiesdidnotmeettheperformancecriteria.Thebinderwasalsonotcompatiblewithasphaltcement.Apyrolysis-hydrogenationprocess,however,producedanoilwhichwassuitableforuseasanextenderofasphaltcementinpavingoperations.BasedonlimitedexperimentsthedurabilityofaHMAwearingcoursemixturecontaininghydrogenatedpyrolysisoilwasnotfoundsignificantlydifferentfromthatcontainingthereferenceasphaltcementonly.Extensivelaboratoryandfieldexperimentsareneededtoevaluatethecompatibilityandperformanceofthecellulosicoilswhenusedwithasphaltcementsfromvarioussources.

WOODLIGNINS

Woodligninisahighvolumewasteproducedinthemanufactureofpaperproducts.AttemptshavebeenmadetoconvertwoodlignintoahighwaybindermaterialanduseiteitheraloneasasubstituteforasphaltcementorasanextenderforasphaltcementinHMAmixes( 4).Suitablelignin-asphaltbinderformulationswerepreparedfromligninsfrombothmajormanufacturingprocesses,thatis,kraftandsulfiteprocesses.Noneofthebinderformulationswassuitablealoneasasubstitutepavingbinder.However,a30percentreplacementofasphaltcementappearedfeasiblewithnosignificanteffectonphysicalproperties.Kraftligninappearedinsolubleinasphaltcement.Lignin-asphaltcementbindersarestifferandrequireslightlyhigherbindercontentthanconventionalHMAmixtures.PrecoatingofthecoarseaggregatehasbeenrecommendedtoreducethebindercontentinHMAmixtures.Basedonlimitedlaboratory

experiments,Terreletal.(4)concludedthatHMAmixturescontaininglignin-asphaltbinderscanbedesignedtomatchthestructuralstrengthofHMAmixturescontainingconventionalmaterials.

BOTTOMASH

BottomAshisawastematerialfromcoalburningpowerplants.Itistheslagwhichbuildsupontheheat-absorbingsurfacesofthefurnace,andwhichsubsequentlyfallstothebottomofthefurnaceandcollectedinanashhopper.Thebottomashiscategorizedasdrybottomashorwetbottomashdependingupontheboilertypeused.Theashwhichisinsolidstateatthefurnacebottomiscalleddrybottomash.Theashwhichisinmoltenstatewhenitfallsinwateriscalledeitherwetbottomashormorecommonlyboilerslag(5).

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ExtensivelaboratorystudieswereperformedonrepresentativesamplesofIndianabottom

ashes,todeterminetheirphysical,chemicalandmechanicalproperties( 6).Dependinguponthesource,bottomashescanhavedifferentphysicalandchemicalproperties.Thesestudiesshowedthatthebottomashesarenon-hazardousinnatureandhaveminimaleffectsongroundwater

quality.However,thebottomashescanbehighlycorrosiveand,therefore,shouldnotbeplacedveryneartoanymetalstructure.

Laboratorystudies(7,8)havealsobeenconductedtoevaluatethefeasibilityofusingbottom

ashesasapartialorfullreplacementofnaturalaggregatesinHMAmixesanddevelopguidelinesfortheiruse.ThepropertiesofHMAcontainingbottomasharedependentonashcontent.Generally,astheashcontentisincreased,theoptimumasphaltcontentisincreased,themixturedensityisdecreased,andtheairvoidsandvoidsinthemineralaggregateareincreased.ThestabilityofHMAmixdecreasesuptoanashcontentof30percentandthenlevelsoff.Themixcontainingbottomashissusceptibletorutting.However,themixishighlyresistanttomoistureinduceddamage(stripping).Itwasconcludedfromthesestudiesthatthepropertiesofmostdryandwetbottomashescanmeetthespecificationsforconventionalaggregates.

Wetbottomash(orboilerslag)canimprovetheskidresistanceofHMAwearingcourses.WestVirginiaobtainedsatisfactoryperformancefromHMAwearingcoursemixescontaining50percentboilerslag(9).LigniteboilerslaghasalsobeenusedtoresurfaceresidentialstreetsinTexas.TheHMAmixcontained75percentboilerslag,25percentlimestonescreenings,and6to7percentasphaltcontent(10).

FLYASH

Flyashisthefineparticulatematterwhichisprecipitatedfromthestacksofpulverizedcoal-firedboilersatelectricalpowergeneratingplants.Itrepresentsnearly75percentofallashwastesgeneratedintheUnitedStates.Thequalityofflyashisaffectedbythetypeofcoalused,theashcontentofthecoal,thedegreetowhichthecdhasbeenpulverizedpriortocombustion,

andtypeofashcollectorsutilized.Thesevariables,therefore,impartawiderangeofphysicalandchemicalpropertiestotheflyash.Itiscomposedoffinelydividedpiecesofsiliceousglasswhichrangefrom1to50micronsindiameter(11).

FlyashhasprimarilybeenusedasamineralfillerinHMAmixturesinseveralstatessuchas

Illinois,Michigan,Montana,NorthDakota,andWestVirginia( 11).Becausetheflyashparticlesareextremelyfine,itisquitelikelytoactasanextenderofasphaltcementinHMAmixtures.Therefore,cautionshouldbeexercisedwhenusingflyashinrut-resistantHMAmixturesforheavydutypavements.

INCINERATORRESIDUE

AccordingtotheestimatesoftheU.S.EnvironmentalProtectionAgency(EPA),about23

millionmegagrams(Mg)ofmunicipalsolidwaste(MSW)wasincineratedintheUnitedStatesin1988(12).Itisprojectedthatabout41millionMgand50millionMgofMSWwillbeincineratedintheyears1995and2000,respectively.Twoashproducts:bottomashandflyash,resultfromincineratingMSW.Bottomashistheunburnedandincombustibleresidueleftontheboilergratesafterincineration,andconsistsoflargeparticles(0.1-100mm)ofslag,glass,rocks,metal,andothermaterials.Flyashconsistsofburnedorpartiallyburnedorganicmaterialparticleswhichareusually1-500microninsize( 5).Theheterogeneouscharacterofthesetwoincineratorresiduescausesawidevariationincompositionfromoneplanttoanother.

TheincineratorresidueisnotsuitableforuseinHMAmixturesunlessitisprocessedfurther.

TheFranklinInstituteResearchLaboratoryinPhiladelphiadevelopedaprocessofdensifying(fusing)theunfusedincineratorresidueandconvertingitintousefulconstructionmaterials.The

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incineratorresidueisgroundwithahammermill,preheatedat688C,andthenmeltedandfused

at1093Ctoformacolumnofsemi-moltenproductwhichislatercooledandcrushedtoaggregatesizes(11).PreliminarylaboratoryevaluationbythePennsylvaniaDepartmentofTransportation(13)indicatedthatthefusedincineratorresiduewasnotsuitableforHMA

mixturesbecauseitdidnotcomplywiththespecifiedgradation,particleswereflatandelongated,andtheHMAmixturedidnotmeetdesigncriteriaforstability,airvoids,orvoidsinthemineralaggregate.Subsequentimprovementsintheprocess( 14,15)producedahighqualityaggregatematerialwhichperformedwellinaHMAsurfacecourseinstallationinHarrisburg,Pennsylvania(16).

SeveralinstallationsusingunfusedincineratorresidueasanaggregateinHMAmixtureswere

madeduringthe1974-1979periodinTexas,Pennsylvania,Washington,DC,andMassachusetts(2).Detailsoftheseinstallationsaregivenintheliterature( 17,18,19,20,21,22).Thefollowingrecommendationshavebeenmade:(a)residuesshouldbewell-burnedout(lossonignitionshouldbelessthan10percent),(b)HMAmixturesforbasecoursescontaining50percentnaturalaggregateand50percentincineratorresidueholdthemostpromise,and(c)2percent

limeshouldbeaddedtominimizestrippingproblems.TIRESCRAPRUBBER

About285milliontiresarediscardedeveryyearintheUnitedStates.Ofthese,about55millionareretreadedorreused(resold),andabout42millionaredivertedtovariousalternativeusessuchascombustionforgeneratingpowerandadditivetoHMAmixes.Theremaining188milliontiresareaddedtostockpiles,landfillsorillegaldumps.AccordingtoEPAestimates,2to3billiondiscardedtiresareavailableatthepresenttime( 23).Severalstateshaveenactedlegislationtoregulatethescraptireproblem.Atthenationallevel,Section1038oftheIntermodalSurfaceTransportationEfficiencyAct(ISTEA)of1991specificallyaddressesthestudyanduseofthescraprubberbythehighwayindustry.

Crumbrubberobtainedfromtirescaneitherbeambientground(grindingatroomtemperatureorabove)orcryogenicallyground(grindingbelowembrittlementtemperature,liquidnitrogenisoftenused).Ambientgroundcrumbrubberhasasponge-likesurface.Duetoveryhighsurfaceareathisrubberreactswithasphaltcementreasonablyfast.Cryogenicallygroundrubberusuallyhasundesirableparticlemorphology(structure).Thisprocessproducescleanflatsurfaceswhich,inturn,reducesthereactionratewithhotasphaltcement.Cryogenicallygroundrubberalsogiveslowerelasticrecoverycomparedtotheambientgroundrubber( 24).

Theuseofcrumbrubbertomodifyasphaltcementhasbeendevelopedoverthepast25years.

CrumbrubberisprimarilyusedinHMAmixesbytwoprocesses:

WetProcess(Asphalt-Rubber)

Thewetprocessblendsthecrumbrubberwiththeasphaltcementpriortoincorporatingthebinderintotheproject.Themodifiedbinderiscommonlycalled"asphalt-rubber."Generally,18-26percentcrumbrubber(16mesh)byweightofasphaltcementisreactedwithasphaltcementat190to218/Cfor1to2hours.Theblendisformulatedatelevatedtemperaturestopromotepotentialchemicalandphysicalbondingofthetwoconstituents.Thefirsttechnologywhichappliedthe"wetprocess"iscalledthe"McDonaldProcess."Thisprocessisalsousedforconstructingstressabsorbingmembrane(SAM)andstressabsorbingmembraneinterlayer(SAMI),andmanufacturingcracksealers.SAMisasealcoatwhichusesasphalt-rubberasabinder.WhenSAMisplacedasaninterlayeritiscalledSAMI.

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DryProcess(Rubber-ModifiedMix)

Thisprocessmixesthecrumbrubberwithaggregatebeforeincorporatingtheasphaltcement.About3-5percentofcoarserubberparticles(1.6-6.4mm)byweightofaggregatearegenerally

used.Thenaturalaggregateisusuallygap-gradedtoaccommodatetherubberparticlesasaggregate.Theamountofcrumbrubberusedinthedryprocesscanbe2-4timesthatusedinthewetprocess.Thefirstapplicationofthe"dryprocess"intheUnitedStatesiscalledthe"PlusRideProcess."Ithasbeenclaimedthaticedebondseasilyfromthepavementsurfaceconsistingofrubber-modifiedmixturebecauseofhigherthanusualresiliencyofthemix.

DetailsofWetProcess

Thewetprocess(asphalt-rubber)willnowbediscussedinmoredetail.Toproduceanacceptableasphalt-rubberbinderitisnecessarytoestablishthedigestiontemperatureandtimeforaspecificcombinationofasphaltcementandcrumbrubber.Viscosityoftheblendischeckedatdifferenttimeintervalsduringtheblendinganddigestionprocess.Viscosityoftheblendincreaseswith

digestiontimeandthenlevelsoff.Achievingareasonablyconstantviscosityindicatesthattheinitialreactionisnearlycompleteandthebinderisreadytouse.Thisinitialreactionisnotwellunderstood,butappearstobeduetoachemicalandphysicalexchangebetweentheasphaltcementandrubberparticlesinwhichtherubberswellsinvolumecausinganincreaseinviscosity.Continuedmixingofasphaltcementandrubberafterinitialreactioncanbegintoreducetheviscosityoftheblendastherubberparticlesbreakdownduringmixing.However,breakdownofrubberparticlesisnotrapid,andmayrequireseveralhoursathightemperatures.

Iftheasphalt-rubberblendistooviscousanextenderoilisusuallyadded.However,iflessthan

10percentcrumbrubber(byweightofasphaltcement)isused,extenderoilisnotneeded.

Theasphalt-rubberblendshouldbeusedassoonaspossibleaftertheinitialreaction.Untilused

itshouldberecirculatedcontinuously.Blendshavebeenallowedtocoolinstoragetanksand

reheatedpriortousewithoutdifficulty.Whenasphalt-rubberbinderisusedinHMAmixesthefollowingmixingtemperatureranges

havebeenused:

Dense-gradedHMAmixes:163-190C

Open-gradedHMAmixes:135-163C

Stackemissionscanbehigherbecauseoftheelevatedmixingtemperatures.

HMAmixescontainingasphalt-rubberbindershouldnotbesubjectedtoprolongedstorageina

silo.Processingthemixthroughasurgesiloisacceptable.Dieselfuelshouldnotbeusedontruckbedsasareleaseagentbecauseitmakesthemixstickmoretothebed.Useoflimewater,

soapsolutionorsiliconeemulsionisrecommendedinstead.

Itisnecessarytomaintainthemixtemperaturewithinthedesiredrangeduringplacementofthe

mix.Staticsteelwheelrollersaregenerallyusedforcompaction.Rubber-tiredrollerstendtopick-upthemat.Vibratoryrollerstendtotearandshovethemat.Iftheroadwayhastobeopenedtothetrafficrightaftercompactionandthetraffichasatendencytopick-upthemat,itisrecommendedtoapply0.5-1kgofconcretesandpersquaremeterofthematsurface.

RecyclabilityoftheHMAcontainingcrumbrubberisaveryimportantissuewhichmustbe

addressedbeforeusingscraptirecrumbrubberonalargescale.Thereisnoexperienceatthepresenttimeinrecyclingsuchmixes.Itisquitelikelythatrecyclingthesemixesinthefuturecouldposeairpollutionproblemsduringproduction.Whatwillhappentotheasphalt-rubber

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binderduringrecycling?Howwilltherecycledmixbedesigned?Iftheseconcernsarenot

addresseditmaynotbepossibletorecycletheHMAmixescontainingcrumbrubber.InthatcasewewillhavetodisposetheRAP(reclaimedasphaltpavement)whichwillbemuchworsethantheproblemofdisposingtires.

In1988,underalegislativemandate,theFloridaDepartmentofTransportation(FDOT)beganaconcertedefforttoevaluatethepotentialuseoftirescraprubberinHMApavements.FDOTcommissionedtheNationalCenterforAsphaltTechnology(NCAT)toprepareastate-of-the-artreportontheuseofgroundtirerubber(GTR)inHMAandrecommendastrategytouseGTRinFloridaHMAmixes.Thisreport(24)waspublishedinAugust1989.Sincethen,FDOThasconstructedthreedemonstrationprojects.AtthepresenttimeFDOTisimplementingthefollowingrecommendations:

UseGTRinfrictioncoursesonly.TypicallyFDOTresortsto75mmcoldmilling(25mmfrictioncourse+50mmstructuralcourse)whichisrecycled.IfthefrictioncoursecontainsGTR,only1/3oftheRAPwillcontainGTR.

Dense-gradedfrictioncourses:Use3-5percentGTRbyweightofasphaltcement.In

thepast,18-20percentGTRhasbeenusedasmentionedearlier.UseNo.80meshGTR.Inthepast,16meshGTRhasgenerallybeenused.FinerGTRisappropriatefortheFloridafrictioncoursemixeswhichapproachsand-asphaltmixtures.Moreover,thefinerGTRsizereactswithasphaltcementmoreeasily,andthusacontinuousblendingofasphaltcementandGTRbecomespossible.

Open-gradedfrictioncourses:Use5-10percentGTRbyweightofasphaltcement.UseNo.40meshGTR.

FDOTdoesaconsiderableamountofhotrecyclingeveryyear.SincetheRAPwillcontainlow

amountsofGTR,noproblemsareanticipatedinrecyclingtheHMApavementsinthefuture.Itisestimatedthatstate-wideuseofGTRwillincreasethepriceofHMAmixesinFloridaby15percent.

NewConceptsThe"McDonaldprocess"(wetprocess)and"PlusRide"(dryprocess)asdiscussedearlierarepatentedprocesses.However,theoriginalpatentonthe"McDonaldprocess"hasexpiredin1992.Recentlysomenewerconceptswhichincludethegenericdryprocess,chunkrubberasphaltconcreteandcontinuouslyblendedasphaltrubber,havebeenintroduced( 23).

Thegenericdryprocessallowsincorporationofcrumbrubberinavailable"generic"aggregate

gradationratherthangap-gradedaggregaterequiredinthePlusRidesystem.ExperimentalfieldapplicationsofgenericdryprocesshavebeenmadeinNewYork,Florida,Iowa,Kansas,Oregon,andIllinois(23).

ChunkrubberasphaltconcreteconcepthasbeendevelopedbytheColdRegionsResearchand

EngineeringLaboratory(CRREL)oftheU.S.ArmyCorpsofEngineers.Thisconceptusesalargemaximumcrumbrubbersize(4.75-12.5mm),andanaggregategradationtoprovidespacefortherubberaggregate.However,thisconcepthasbeenconfinedtolaboratoryonlyandnofieldinstallationshavebeenmade.

ThecontinuousblendingasphaltrubberconcepthasbeenusedbyFloridaDOT(FDOT)as

describedearlier.Itisawetprocesswhichusesfinecrumbrubber(180:orNo.80mesh)toavoidreactiontanks,andtofacilitatecontinuousblending.TheperformanceofFDOTexperimentalsectionsisbeingmonitored.

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WASTEGLASS

WhencrushedwasteglassisincorporatedinHMAmixtheresultingmixtureissometimesreferredtoas"glasphalt."

Severallaboratoryandfieldevaluationsofglasphaltwereconductedintheearly1970sintheU.S.andCanada.Afternosignificantinterestforadecade,thepotentialuseofglasphaltisnowbeingreassessed.ThreestatesConnecticut,VirginiaandFloridahaverecentlyconductedfeasibilitystudiesandissuedresearchreports( 25,26,27).

TheConnecticutreportgivesanexcellentreviewofliteratureonbothlaboratoryandfield

evaluationsofglasphaltsince1969:Glasphaltwassuccessfullymixedandplacedinatleast45locationsintheU.S.and

Canadabetween1969and1988.However,mostglasphalthasbeenplacedoncitystreets,drivewaysandparkinglots,andnotonhigh-volume,high-speedhighways.

Potentialproblemswithglasphaltinclude:lossofadhesionbetweenasphaltand

glass;maintenanceofanadequatelevelofskidresistance,especiallywithcoarseparticles;breakageofglassandsubsequentraveningunderstuddedtires;lackofadequateandconsistentsupplyofglass;andincreasedproductioncosts(estimatedat$5/MgmorethantheconventionalHMAmixinConnecticut).

Glasphaltshouldbeusedonlyasabasecoursetoalleviatepotentialskidresistanceandsurfaceraveningproblems.

Nomorethanamaximumof9.5mmglassshouldbeusedinglasphak,withhydratedlimeaddedtopreventstripping.

TheVirginiareportisbasedonlaboratoryevaluationandeconomicanalysisofglasphalt.Two

glasscontents,5percentand15percent,andtwoasphaltcontentswereusedinthelaboratoryevaluationofVirginiaS-5surfaceHMAmix(12.5mmtopsize).Adenselygradedrecycledglasswithamaximumnominalsizeof9.5mmwasused.

Thefollowingaresignificantconclusions:

TheuseofglasstendstoreducetheVMAandairvoidsinMarshallspecimens;therefore,optimumasphaltcontentwillalsobereduced.

Neitherresilientmodulusnorindirecttensilestrengthsareadverselyaffectedbytheadditionofupto15percentglass.

Althoughbothwetstrengthandretainedtensilestrengthlaties(TSR)wereunaffectedbythepercentageofglass,someseparationattheasphalt/glassinterfacewasobserved.

Amaximumof15percentcrushedrecycledglassshouldbeallowed(100percentpassinga9.5mmsieveandamaximumof6percentpassinga75pmsieve)inHMAmixes.

Thereislittlemonetaryincentivetouserecycledglassatthepresenttimebecausethecostofglassvariesconsiderably.Anexperimentalsectionshouldbelaidpriortoextensiveuseofwasteglass.

TheFloridaDepartmentofTransportationtestedthreeHMAmixturestodeterminetheeffectsof

crushedglass:1.Controlmix(9.5mmnominalmaximumsize)2.15percentcoarseglassmixturesameasthecontrolmixtureexceptthat15percent

ofthescreeningswerereplacedwithcoarse(9.5mm-2.06mmnominalsize)crushedglass.

3.15percentfineglassmixturesameasthecontrolmixtureexceptthat15percentofthescreeningswerereplacedwithfine(2.06mm-75:mnominalsize)crushedglass.

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AC-30asphaltcementwithandwithoutantistrippingagentwasusedtoprepareMarshall

specimenswhichwerealsotestedfortensilestrength.Thefollowingconclusionsweredrawnbasedonthelimitedlaboratoryevaluation:

Marshallstabilityvaluesdecreasedby15-20percentanddryindirecttensilestrengthdecreasedby20percentwhen15percentofthescreeningswerereplacedwitheithercoarseorfineglass.

MoistureconditioningofMarshallspecimenscauseda15percentand50percentdecreaseintensilestrengthwhencoarseandfineglass,respectively,wereincorporatedintothemixture.Retainedtensilestrengthratio(TSR)valuesindicatedthattheantistrippingadditivewasineffectiveinreducingthemoisturedamage.

ItisunlikelythattheuseofcrushedglassinHMAmixtureswillbeeconomicallyfeasiblewhensuitablelocalmaterialsareavailableatorneartheHMAfacility.

TheCityofNewYorkplaces360,000MgofHMAcontaining10percentwasteglassevery

year.Thisamountstoanannualconsumptionof36,000Mgofglass.

ROOFINGSHINGLES

Approximately90millionroofingshinglesquaresareproducedperyearby77plantsintheUnitedStates.About1/3oftheshinglesareusedonnewhousesandtheremaining2/3oftheshinglesareusedforreroofinghouses.Whenahouseisreroofed,oftenanequivalentamountofoldshinglesisremovedanddiscarded.Moreover,eachroofingplantgeneratesscrapmaterialsandsecondsthatcanrangefrom5to10percentoftheproductioncapacity.Thedisposalofoldshinglesandthescrapmaterialhascreatedadifficultdisposalproblem( 28).

Itisestimatedthatroofingwastecontainsabout36percentasphaltcontent,22percenthardrock

granules(minusNo.10),8percentfillerandsmalleramountsofmiscellaneousmaterials( 29).

RoofingshingleshavebeenusedsuccessfullyintheHMApavingoftheparkinglotsatDisney

World,Florida.Shinglesneedtobeshreddedtoatleast12.5mmorsmallerpriortointroductioninthemixtoensuremeltdownanduniformdispersionintheHMAmixture.Accordingtocostestimates(28),theHMAcostcanbereducedby$3.08permegagram(Mg)byintroducingonly5percentorganicshingles.

COALMINEREFUSE

AnthraciteCoalRefuse

TheprincipalsourceofanthracitecoalisinnortheasternPennsylvania.Anthracitecoalminerefuseiscomposedofunprocessedminerefuseandprocessedcoalbreakerrefuse.Itisagrayslate-likematerialcontainingoxidesofsilicon,aluminum,iron,calcium,magnesium,sodiumandpotassium.Morethan50percentofaverageanthraciterefuseisgreaterthan25.4mminsize

(11).

ThePennsylvaniaDepartmentofTransportation(PennDOT)conductedalaboratoryevaluation

ofunburnt(raw)anthraciterefuseasanaggregateinHMAmixtures( 30).Theaggregateparticleswereveryabsorptive,particularlyinsizeslargerthanthe4.75mmsieve,andcouldnotbecoatedcompletelywithasphaltcement.Freeze-thawfailuresalsooccurredinlessthanhalfthecyclesofacontrolmix.AnthraciterefusemustbeincineratedbeforeuseintheHMAmix.FourHMApavingprojectsinLuzemeCountyofPennsylvaniawereconstructedwithcrushedincineratedanthraciterefuse(31).Theperformanceintermsofskidresistanceandwearwasreportedtobesatisfactory.

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BituminousCoalRefuse

TheprincipalsourcesofbituminouscoalarelocatedinKentucky,WestVirginiaandPennsylvania.Bituminouscoalrefuseissomewhatsimilartoanthraciterefuseinappearance.

TheUniversityofKentuckyevaluatedtheuseofbituminouscoalrefuseinHMAmixturesin1964(32).Themixturescontaining100percentcoalrefuseweresusceptibletomoistureinduceddamage.

SUMMARY

Recyclingofwastematerialsinhighwayconstructionshouldbeencouraged.However,itisnecessarytoaddresstheengineeringconcerns,environmentalconcernsandeconomicconcernsmentionedinthispaperbeforeanylargescaleuseofthesematerials.Theuseofwastematerialsshouldnotbemandated.HMAcontainingawastematerialshouldperformaswellorbetterthanconventionalHMA.Itshouldalsobeenvironmentallysafebothforthefirstconstructionandfuturerecyclability.

Thispaperdiscusseslaboratoryand/orfieldevaluationofseveralwastematerialswhichhavebeenusedinHMA.ItisrecommendedtoconstructdemonstrationprojectstoevaluatetheperformanceofHMAcontainingwastematerials.Wastematerialsshouldnotbeusedasastandardpracticeuntiltheperformancedataisavailablefromthedemonstrationprojects.REFERENCES1.

2.

3.4.

5.

6.

7.8.

9.10.

11.

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Warren,Jim,"TheUseofWasteMaterialsinHotMixAsphalt."NAPASpecialReport152,June25,1991.Ormsby,W.C.andD.G.Fobs,"UseofWasteandBy-ProductsinHighwayConstruction."PaperpresentedattheAnnualMeetingofTRB,January1991.

Butte,W.A.,E.M.KohnandE.G.Scheibel,"HighwayBinderMaterialsfromCellulosicandRelatedWastes."FHWAReportNo.FHWA/RD-130,December1980.Terrel,R.L.etal.,"EvaluationofWoodLigninasaSubstituteorExtenderofAsphalt."FHWAReportNo.FHWA/RD-80/125,October1980.Ahmed,I.,"UseofWasteMaterialsinHighwayConstruction."JointHighwayResearchReport,ProjectC-36-50K,PurdueUniversity,May1991.Ke,T.C.,"ThePhysicalDurabilityandElectricalResistivityofIndianaBottomAsh."ResearchReportNo.FHWA/IN/JHRP-9076,PurdueUniversity,1990.Majidzadeh,K.,"UsersManual-PowerPlantBottomAshinBlackBaseandBituminousSurfacing:State-of-the-ArtReport."FHWAReportNo.FHWA-7-77-148,September1979.Majidzadeh,K.,"ExecutiveSummary-PlantBottomAshinBlackBaseandBituminousSurfacing."FHWAReportNo.FHWA-RD-79-72,September1979.

Moulton,LK.,Seals,R.K.,andAnderson,D.A.,"BottomAsh:AnEngineeringMaterial."JournaloftheSoilMechanicsandFoundationsDivision,AmericanSocietyofCivilEngineers,Vol.98,No.SM4,April1972,pp.311-325."LigniteSlagPavestheWay."IndustrialandEngineeringChemistry,Vol.51,No.7,July1959,pp.37A-38A.Miller,R.H.andCollins,R.J.,"WasteMaterialsasPotentialReplacementsforHighwayAggregates."NCHRPReport166,TransportationResearchBoard,1976."CharacterizationofMunicipalSolidWasteintheUnitedStates:1990Update."ReportNo.EPA/530-SW-042,U.S.EnvironmentalProtectionAgency,1990.Kandhal,P.S.andWenger,M.E.,"IncineratorRefuseasanAggregateinBituminousConcrete."PennsylvaniaDepartmentofTransportation,BureauofMaterials,TestingandResearch,April1971.

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Pindzola,D.andR.C.Chou,"SyntheticAggregateforIncineratorResiduebyaContinuousFusionProcess."FHWAReportNo.FHWA/RD-74/23,1974.Pindzola,D.,"LargeScaleContinuousProductionofFusedAggregatefromIncineratorResidue."FHWAReportNo.FHWA/RD-76/l15,1976.

Snyder,R.R.,"EvaluationofFusedIncineratorResidueasaPavingMaterial."FHWAReportNo.FHWA-TS-88-229,1980.Haynes,J.,andLedbetter,W.B.,"IncineratorResidueinBituminousBaseConstruction."ReportFHWA/RD-76/12,FederalHighwayAdministration,1976.Teague,D.J.,andLedbetter,W.B.,"ThreeYearResultsonthePerformanceofIncineratorResidueinBituminousBase."ReportFHWA/RD-78/144,FederalHighwayAdministration,1978.Erdeley,J.,andLedbetter,W.B.,"FieldPerformanceofLittercrete(IncineratorResidue)inBituminousBase."ReportFHWA/RD-88/022,FederalHighwayAdministration,September,1981.Pavlovich,R.D.,Lentz,H.J.,Ormsby,W.C.,"IncineratorResidueasAggregateforHot-MixAsphaltBaseCourse."TransportationResearchRecord734,1979,pp.38-44.Griffith,

J.L.,"SummaryUpdateofResearchProjectswithIncineratorBottomAshResidue."CommonwealthofMassachusetts,ExecutiveOfficeofEnvironmentalAffairs,DepartmentofEnvironmentalManagement,BureauofSolidWasteDisposal,Boston,MA,1982.Turo,M.D.,andLeonido,A.M.,"IncineratorResidueasaComponentofBituminousPavements."MassachusettsDepartmentofPublicWorksReportR-37-O,1984.Heitzman,M.S.,"StateofthePractice-DesignandConstructionofAsphaltPavingMaterialswithCrumbRubberModifier."ReportFHWA-SA-92-022,FederalHighwayAdministration,May1992.Roberts,F.L.,P.S.Kandhal,E.R.BrownandR.L.Dunning,"InvestigationandEvaluationofGroundTireRubberinHotMixAsphalt."NCATReport89-3,August1989.Larsen,D.A.,"FeasibilityofUtilizingWasteGlassinPavements."Connecticut

DepartmentofTransportation,ReportNo.343-21-89-6,June1989.Hughes,C.S.,"FeasibilityofUsingRecycledGlassinAsphaltMixes."VirginiaTransportationResearchCouncil,ReportNo.VTRC90-R3,March1990.Murphy,K.H.,R.C.West,andG.C.Page,"EvaluationofCrushedGlassinAsphaltPavingMixtures."FloridaDOTResearchReportNo.FL/DOT/SMO/91-388,April1991.Brock,J.D.,andShaw,D.,"FromRoofingShinglestoRoads."TechnicalPaperT-120,AstecIndustries,Chattanooga,TN,1989.Paulsen,G.,Stroup-Gardiner,M.,andEpps,J.,"RoofingWasteinAsphaltPavingMixtures."CenterforConstructionMaterialsResearch,UniversityofNevada,Reno,1988.Wenger,M.E.andSchmidt,G.H.,"AnthraciteRefuseasanAggregateinBituminousConcrete."PennsylvaniaDepartmentofTransportation,ResearchProjectNo.70-8,June1970.

Mellott,D.B.,"AnthraciteRefuseinID-2ABituminousConcrete."PennsylvaniaDepartmentofTransportation,ResearchProjectNo.70-8,July23,1970.Howard,G.G.,"ALaboratoryInvestigationofthePropertiesofCoal-BitumenPavingMixtures."UniversityofKentucky.EngineeringResearchBulletinNo.71.March1964.

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waste materials in hot mix asphalt: an overview

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