Design, Construction, and Performance of New Generation Open Graded Friction Course (OGFC)
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Transcript of Design, Construction, and Performance of New Generation Open Graded Friction Course (OGFC)
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DESIGN,CONSTRUCTION,ANDPERFORMANCEOFNEW-GENERATIONOPEN-GRADEDFRICTIONCOURSES
By
RajibB.Mallick
PrithviS.KandhalL.AllenCooley,Jr.DonaldE.Watson
ThispaperwaspublishedintheJournaloftheAssociationofAsphaltPavingTechnologists,AsphaltPavingTechnology,Volume69,2000
277TechnologyParkway Auburn,AL36830
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DESIGN,CONSTRUCTION,ANDPERFORMANCEOFNEW- GENERATIONOPEN-GRADEDFRICTIONCOURSES
By
RajibB.Mallick
AssistantProfessorWorcesterPolytechnicInstituteWorcester,Massachusetts
PrithviS.Kandhal
AssociateDirectorNationalCenterforAsphaltTechnology
AuburnUniversity,Alabama
L.AllenCooley,Jr.ResearchEngineer
NationalCenterforAsphaltTechnologyAuburnUniversity,Alabama
DonaldE.Watson
GeorgiaDepartmentofTransportationForestPark,Georgia
ThispaperwaspublishedintheJournaloftheAssociationofAsphaltPavingTechnologists,AsphaltPavingTechnology,
Volume69,2000
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DISCLAIMER
Thecontentsofthisreportreflecttheviewsoftheauthorswhoaresolelyresponsibleforthefactsandtheaccuracyofthedatapresentedherein.ThecontentsdonotnecessarilyreflecttheofficialviewsandpoliciesoftheNationalCenterforAsphaltTechnologyofAuburnUniversity.Thisreportdoesnotconstituteastandard,specification,orregulation.
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ABSTRACT
Open-gradedfrictioncourse(OGFC)hasbeenusedbyseveralstatedepartmentsof
transportation(DOT)since1950.WhilemanyDOTsreportgoodperformance,manyotherstatesstoppedusingOGFCduetounacceptableperformanceand/orlackofadequatedurability.Avastmajorityofthestatesreportinggoodexperienceusepolymermodifiedasphaltbindersandarelativelycoarseraggregategradationcomparedtotheotherstatesreportingunsatisfactoryperformance.Obviously,thereisaneedtodevelopanimprovedmixdesignproceduretohelpthehighwayagenciesinsuccessfuluseofOGFC.
TheprimaryobjectivesofthisstudyaretoevaluatetheperformanceofOGFCinthelaboratory
withdifferentgradationsandtypesofadditives,andrecommendarationalmixdesignprocedureforthenew-generationOGFCmixes.Additionally,theconstructionandperformanceofsixOGFCpavements(constructedpriortothisstudy)arediscussed.ThesemixesgenerallymeettherequirementsforgradationbandandCantabroabrasionrecommendedinthenewmixdesignsystem.
SeveralpolymersandfiberswereusedinOGFCmixes.Themixeswereevaluatedfordraindown,permeability,Cantabroabrasion,rutting,andmoisturesusceptibility.Atentativemixdesignsystemforthecoarsenew-generationOGFChasbeenrecommended.BasedupontheevaluationofsixOGFCfieldpavements,ithasalsobeenshownthatOGFCmixesmeetingthenewmixdesignrequirementsareconstructibleandhaveexhibitedgoodperformance.
KEYWORDS:open-gradedfrictioncourse,OGFC,mixdesign,polymermodifiedbinder,fiber,
draindown,abrasion,permeability,moisturesusceptibility
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DESIGN,CONSTRUCTION,ANDPERFORMANCEOFNEW-GENERATIONOPEN-
GRADEDFRICTIONCOURSES
RajibB.Mallick,PrithviS.Kandhal,L.AllenCooley,Jr.,andDonaldE.Watson
INTRODUCTIONOpen-gradedfrictioncourse(OGFC)hasbeenusedsince1950indifferentpartsoftheUnitedStatestoimprovethesurfacefrictionalresistanceofasphaltpavements.OGFCimproveswetweatherdrivingconditionsbyallowingthewatertodrainthroughitsporousstructureawayfromtheroadway.Theimprovedsurfacedrainagereduceshydroplaning,reducessplashandspraybehindvehicles,improveswetpavementfriction,improvessurfacereflectivity,andreducestrafficnoise.TheFederalHighwayAdministration(FHWA)developedamixdesignprocedureforOGFC(1)in1974,whichwasusedbyseveralstatedepartmentsoftransportation(DOTs).WhilemanyDOTsreportedgoodperformance,manyotherstatesstoppedusingOGFCdueto
unacceptableperformanceand/orlackofadequatedurability(2).However,significantimprovementshavebeenmadeduringthelastfewyearsinthegradationandbindertypeusedin
theOGFC.Recently,asurvey(3)ontheexperienceofstateswithOGFCwasconductedbytheNationalCenterforAsphaltTechnology(NCAT).AlthoughexperienceofstateswithOGFChasbeenvaried,halfofthestatessurveyedinthisstudyindicatedgoodexperiencewithOGFC.Morethan70percentofthestateswhichuseOGFCreportedservicelifeofeightormoreyears.About80percentofthestatesusingOGFChavestandardspecificationsfordesignandconstruction.Avastmajorityofstatesreportinggoodexperienceusepolymermodifiedasphaltbinders.Also,gradationsofaggregatesusedbythesestatestendtobesomewhatcoarsercomparedtogradationsusedearlierandgradationsusedbyotherstates.ItseemsthatgooddesignandconstructionpracticeisthekeytoimprovedperformanceofOGFCmixes.ThereisaneedtodevelopanimprovedmixdesignproceduretohelpthestatesinsuccessfuluseofOGFC.Awell-designedandwell-constructedOGFCshouldnothaveraveling/delaminationproblems
andshouldreasonablyretainitshighpermeabilityandmacrotexture.
Objective
TheprimaryobjectiveofthisstudywastoevaluatethelaboratoryperformanceofOGFCwithdifferentgradationsandtypesofadditives,andbaseduponthisworkrecommendarationalmixdesignsystemforanew-generationOGFC.Additionally,theconstructionandperformanceofsixOGFCpavements(constructedpriortothislaboratorystudy)arediscussed.ThesemixesgenerallymeettherequirementsforgradationbandandCantabroabrasionrecommendedinthenewmixdesignsystem.
SCOPEOFWORK
ThemajorperformanceproblemsassociatedwithOGFCcanbeclassifiedintotwocategories:ravelinginOGFCandstrippinginunderlyingasphaltcourses.ThemajorcausesofravelinginOGFCarebelievedtobeinadequateasphaltbinderfilmthickness,excessiveagingofbinder,andlossofasphalt-aggregateadhesionunderfreeze-thawconditions.WhenOGFCwaspromotedbytheFederalHighwayAdministration(FHWA)inthe1970s,manystateseitheradoptedFHWA'smixdesignmethod(1)orusedarecipemixcomposition.Sincepolymermodifiedasphaltbinderswerenotavailableatthattime,andnofiberswereused,designasphaltcontentsinOGFCmixeswerekeptrelativelylowbecauseofbinderdraindownproblemsduringstorageand/ortransportation.SomestatesalsoexperiencedsignificantlossinpermeabilityofOGFCafter2-3yearsbecauseofcloggingofvoidsbydeicingmaterialsorotherdebris.
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Thefollowingquestionswereraisedtodevelopatestplanforevaluatingdifferentgradationsand
additivesinthisstudy:1)WhatisagoodgradationforOGFCtoprovide
a)adequatepermeabilitytodrainwaterquicklyandmaintainareasonable
permeabilityduringservicelife?b)adequatestabilitythroughstone-on-stonecontacttominimizerutting?
2)Whatkindofadditive(s)isneededtoa)preventdraindownofbinderatbindercontentsneededtoprovidesufficient
binderfilmthickness?b)improveruttingresistanceanddecreasetemperaturesusceptibility?c)resistexcessiveaging?
Toanswerthesequestions,thestudywasdividedintotwomainparts.First,alaboratorystudy
wasconductedtoevaluatedifferentOGFCgradationsandtypesofadditives.Baseduponthislaboratorywork,anewOGFCmixdesignsystemwastoberecommended.Withinthenewdesignsystem,gradationbands,volumetricproperties,andperformancerelatedtestsweretobe
identified.ThesecondpartofthestudyentailedidentifyingOGFCpavementsectionsthatwouldcloselyresembleOGFCmixesresultingfromtherecommendedmixdesignsystemanddocumentconstructionandperformance.
LaboratoryStudy
AflowchartforthelaboratorystudytestplanisshowninFigure1.InthefirstphaseofthestudyblendswerepreparedwithgradationssimilartoandcoarserthantheFHWArecommended(1)gradationforOGFCmixes.Table1andFigure2givetheFHWAgradationandtheotherthreenewgradationsevaluatedinthisstudy.TheFHWAgradationhas40percentmaterialpassingthe4.75mmsieve,andthecoarsestoftheotherthreegradationshas15percentmaterialpassingthe4.75mmsieve.ThecoarsestgradationisverysimilartothegradationthatisbeingusedbymanystatesreportinggoodexperiencewithOGFCmixes(suchasGeorgia).Mixeswerepreparedfor
theseblendswithanunmodifiedPG64-22asphaltbinder.ThepropertiesofaggregateandasphaltbinderareshowninTables2and3,respectively.MixdesignswereconductedaccordingtoFHWAprocedures(1).Thesefourblendswereevaluatedforstone-on-stonecontactwithvoidsinthemineralaggregate(VMA)andvoidsinthecoarseaggregate(VCA)plots,andVCAdatafromdryroddedtestswithcoarseaggregatesfractiononly.TheVCAconceptisusedinthedesignofstonematrixasphalt(SMA)mixtures( 4).
SamplespreparedwithFHWAgradationandcoarsergradationsweretestedfordraindown
potential,permeability,abrasionresistance,agingpotential,andrutting.Thetestproceduresarediscussedlater.Allsampleswereinitiallycompactedwith100gyrationsofSuperpavegyratorycompactor,whichwereconsideredtobeequivalentto50blowsofMarshallhammerinSMAmixdesign.Theprimaryobjectiveofphase1wastoevaluatetherelativeimprovementsinmixcharacteristicswhentheFHWAgradationismadecoarserandcoarser.
Inthesecondphaseofthestudy,mixeswerepreparedwiththecoarsestgradation(gradation#3
inTable1)andsixdifferentbinders:PG64-22,PG64-22plusStyrene-Butadiene-StyreneorSBS(referredtohereinafterasPG64-22-SBS),PG76-22containingStyreneButadieneorSB(referredtoasPG76-22-SB),PG64-22pluscellulosefiber(referredtoasPG64-22-CF),PG76-22containingStyreneButadieneandslagwool(referredtoasPG76-22-SB-SW)andPG64-22plusslagwool(referredtoasPG64-22-SW).BothSBSandSBwereaddedtotheasphaltbinderat4percentbyweightofbinder.ThePG64-22and76-22(withSB)binderswerethebasebinders,towhichthedifferentadditiveswereadded.ThepropertiesofPG64-22and76-22(withSB)bindersareshowninTable3.Celluloseandmineralfiber(slagwool)wereaddedat0.37percentbyweightofthetotalmix.TheprimaryobjectiveofthesecondphasewastoevaluatetheperformanceofvariousadditivesintheOGFCmix.Basedondiscussionwithpersonnelfromthe
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Figure1.TestPlan3
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Table1.GradationsUsed
PercentPassingSieveSize Original Gradation New New New
FHWA Similarto Gradation#1Gradation#2 Gradation#3Gradation FHWAUsed
19mm --- 100 100 100 100
12.5mm 100 95 95 95 95
9.5mm 95-100 65 65 65 65
4.75mm 30-50 40 30 25 15
2.36mm 5-15 12 77 70.075mm 2-5
433 3
100
90
80
70
6050
40
30
20
10
0
0 0.0.20.0150.03075 .4 .6 0..680 1181.21. 1.4361.62. 1.8 4.752 2.2 2.4 2.69.52.8 312.53.2 3.4 3.6 193.8 4
SieveSize
FHWAgradation,40%passing4.75mmsieve 30%passing4.75mmsieve25%passing4.75mmsieve 15%passing4.75mmsieve
Figure2.GradationsUsedintheStudy
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PercentPassin
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GeorgiaDepartmentofTransportation(GDOT),thesemixeswerepreparedwith6.5percent
asphaltbinder,andcompactedwith50gyrationstomatchairvoidcontentsofOGFCcoresamplesobtainedfromthefieldwheresimilargradationhadbeenused.Thesemixeswerealsotestedforthedifferentpropertiesmentionedearlier.Resistancetomoisturedamagewasalso
evaluatedinphase2.
Table2.PropertiesofAggregates
Aggregate
Granite
Size
Fine
Coarse
Property
BulkSpecificGravity
WaterAbsorption,percent
FineAggregateAngularity
BulkSpecificGravity
WaterAbsorption,percent
Value
2.712
0.63
49.5
2.688
0.58
Table3.PropertiesofPG64-22and76-22(withSB)AsphaltBinder
Asphalt HighTemperatureproperties LowTemperatureProperties Binder(PG) Temp
oeratureC
OriginalDSR,G*/Sin*
RTFOTDSR,G*/Sin*
TempoeratureC
RTFOT+PAV,DSR,
TempoeratureC
RTFOT+PAV
(kPa) (kPa) G*Sin* Creep m(Mpa) Stiffness, (slope)
S(MPa)
64-22 64 1.784 3.258 22 4426 -12 240 0.317
76-22 76 1.478 2.356 31 4450 -12 155 0.32(withSB)
FieldStudyTovalidatethepotentialforthenewmixdesignsystem,OGFCpavementswerefoundthatwouldcloselymeetrequirementsforthenewmixdesignsystem.SixOGFCpavementsectionswerelocatedonInterstate75southofAtlanta,Georgia.Thesesectionswereconstructedin1992andconsistofOGFCmixeswithdifferenttypes/combinationsofasphaltadditives.
ConstructionofthesesixpavementswasdocumentedinaGDOTreport(5).Additionally,
representativesofNCATperformedavisualdistresssurvey.Duringthesurvey,rutdepthsforeachsectionandthreecorespersectionwereobtained.Thecoreswereusedtomeasuredensityandlaboratorypermeability.
LABORATORYTESTPROCEDURES
Thefollowingtestprocedureswereusedinthelaboratorystudy.
VoidsinCoarseAggregate(VCA)
Similartostonematrixasphalt(SMA),OGFCmusthaveacoarseaggregate(retainedonNo.4.75mm)skeletonwithstone-on-stonecontacttominimizerutting(4).Theconditionofstone-
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on-stonecontactwithinanOGFCmixisdefinedasthepointatwhichthevoidsincoarse
aggregate(VCA)ofthecompactedOGFCmixtureislessthantheVCAofthecoarseaggregatealoneinthedryroddedtest(AASHTOT19).TheVCAofthecoarseaggregateonlyfraction(VCADRC)isdeterminedbycompactingthestonewiththedry-roddedtechniqueaccordingtoAASHTOT19.Whenthedry-roddeddensityofthestonefractionhasbeendetermined,theVCA
DRCcanbecalculatedusingthefollowingequation:
where,GCA(s
(w
=bulkspecificgravityofthecoarseaggregate(AASHTOT85)=unitweightofthecoarseaggregatefractioninthedry-roddedcondition
(kg/m3)(AASHTOT19)
=unitweightofwater(998kg/m3
)DraindownCharacteristicsTheNCATdraindowntestmethod(4)wasused.Asampleoflooseasphaltmixturetobetestedispreparedinthelaboratoryorobtainedfromfieldproduction.Thesampleisplacedinawirebasketwhichispositionedonaplateorothersuitablecontainerofknownmass.Thesample,basket,andplateorcontainerareplacedinaforceddraftovenforonehouratapre-selectedtemperature.Attheendofonehour,thebasketcontainingthesampleisremovedfromtheovenalongwiththeplateorcontainerandthemassoftheplateorcontainerisdetermined.Theamountofdraindownisthencalculated.
Thistestmethodcanbeusedtodeterminewhethertheamountofdraindownmeasuredforagivenasphaltmixtureiswithinacceptablelevels.Thetestprovidesanevaluationofthedraindownpotentialofanasphaltmixtureduringmixturedesignand/orduringfieldproduction.Thistestisprimarilyusedformixtureswithhighcoarseaggregatecontentsuchasporousasphalt(OGFC)andSMA.Amaximumdraindownof0.3percentbyweightoftotalmixisrecommendedforSMAandisalsoconsideredapplicabletoOGFC.
Permeability
TheFloridaDOTfalling-headlaboratorypermeabilitytestwasused.Thistestusesafallingheadconcepttodeterminepermeability(6).
ResistancetoAbrasion
TheresistanceofcompactedOGFCspecimenstoabrasionlosswasanalyzedbymeansoftheCantabrotest(7).ThisisanabrasionandimpacttestcarriedoutintheLosAngelesAbrasionmachine(ASTMMethodC131).
Inthistest,anOGFCspecimencompactedwith50blowsoneachsideisused.Themassofthe
specimenisdeterminedtothenearest0.1gram,andisrecordedasP1.ThetestspecimenisthenplacedintheLosAngelesRattlerwithoutthechargeofsteelballs.Theoperatingtemperatureisusually25C.Themachineisoperatedfor300revolutionsataspeedof30to33rpm.Thetestspecimenisthenremovedanditsmassdeterminedtothenearest0.1gram(P
2).Thepercentage
abrasionloss(P)iscalculatedaccordingtothefollowingformula:
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Therecommendedmaximumpermittedabrasionlossvalueforfreshlycompactedspecimensis20percent(5).However,someEuropeancountriesspecifyamaximumvalueof25percent.
Resistancetoabrasionusuallyimproveswithanincreaseinbindercontent.However,this
resistanceisalsorelatedtotherheologicalpropertiesofthebinder.Foragivengradationandbindercontent,mixescontainingunmodifiedbindersgenerallyhavelessresistancetoabrasionthanmixescontainingpolymer-modifiedbinders.
Aging
BothunagedandagedcompactedOGFCweresubjectedtoCantabroabrasiontesttoevaluatetheeffectofacceleratedlaboratoryagingonresistancetoabrasion.Becauseofveryhighairvoid
contentstheasphaltbinderinOGFCispronetohardeningatafasterratethandense-gradedhotmixasphalt(HMA),whichmayresultinreductionofcohesiveandadhesivestrengthleadingtoraveling.Therefore,themixdesignshouldbesubjectedtoanacceleratedagingtest(7).
AgingwasaccomplishedbyplacingfiveMarshallspecimenscompactedwith50blowsina
forceddraftovensetat60Cfor168hours(7days).Thespecimensarethencooledto25Candstoredfor4hourspriortoCantabroabrasiontest.Theaverageoftheabrasionlossesobtainedon5agedspecimensshouldnotexceed30percent,whilenoindividualresultshouldexceed50percent.
FreezeandThawTestforResistancetoMoistureDamage
RavelingoftheOGFCmaytakeplaceduetostrippinginthemix,especiallyfromfreezeand
thawcyclesinnortherntierstateswithcoldclimates.ModifiedLottmantest(AASHTOT283)wasusedinthisstudy.Insteadofusingonefreeze/thawcycleusedfordense-gradedHMA,5cycleswereusedforOGFC.SincetheairvoidcontentishigherintheOGFCcomparedtodense-gradedHMA,moresevereconditioningwasdeemednecessarytoevaluatethestrippingpotential.
Rutting
ThepotentialforruttingofOGFCwasevaluatedwiththeAsphaltPavementAnalyzer(APA)whichisamodifiedversionofGeorgialoadedwheeltester.CylindricalOGFCspecimenswereloadedat64C(bothdryandunderwater)for8000cyclesandrutdepthmeasured.
DEVELOPMENTOFMIXDESIGNPROCEDURE
Asummaryofdataandanalysesusedtodevelopthemixdesignsystemarepresentedinthefollowingsections.
PhaseOne
TwoblendswithcoarseaggregateonlywerepreparedaccordingtotheAASHTOT19proceduretodeterminethedryroddedvoidsincoarseaggregate(VCADRC).Next,threeblendswerepreparedforeachgradationwith15%,25%,30%and40%passing4.75mmsieve.Asmentionedearlier,the40%passing4.75mmsieverepresentedFHWAgradationandtheremainingthreegradationswereallcoarserthantheFHWAgradation(Figure2,Table1).Since,ingeneral,theNCATsurveyindicatedgoodperformanceofmixeswithgradationscoarserthan
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theFHWAgradation(3),itwasdecidednottouseanygradationfinerthantheFHWA
gradation.MixeswerepreparedwithPG64-22asphaltbinderandcompactedwith100gyrationsoftheSuperpavegyratorycompactor(SGC).TheasphaltcontentsweredeterminedbytheFHWAmethod(1).TheFHWAmethodconsistsofthefollowingsteps:(1)determinationof
surfacecapacityofaggregatefractionretainedon4.75mmsievebyoilabsorptionmethod,and(2)determinationofasphaltcontentfromanempiricalformulawiththesurfaceconstant(obtainedinstep1).Thefollowingformulaisused:Table4givesthemixdesigndatausingtheFHWAprocedure.Unfortunately,theoptimumasphaltcontentisbasedontheoilabsorptionofthematerialretainedon4.75mmsieveonly.Therefore,theoptimumasphaltcontentsareverysimilarforallfourgradations,whichisnotlogical.Obviously,theFHWAformulawasdevelopedforonegradationband.
Table4.FHWAMixDesignData(PhaseOne)
Gradation(%passing4.75mmsieve)
15
25
30
40
PercentOilRetained(POR)
1.890
1.839
1.808
1.724
SurfaceConstant,Kc
0.856
0.836
0.823
0.789
AsphaltContent,percent
5.55
5.51
5.48
5.42
Theaverageairvoidsorvoidsintotalmix(VTM),voidsinmineralaggregate(VMA),voidsin
coarseaggregate(VCA),andvoidsfilledwithasphalt(VFA)dataforthefourdifferentmixesareshowninTable5.TheVCADRCisalsoshowninTable5.PlotsofVTM,VMA,andVCAareshowninFigures3and4.Althoughthereisadifferenceofonly0.13%inasphaltcontentbetweenthemixeswithfourgradations,thereisasignificantrangeinvoids(VTM,VMAandVCA).TheVTMandVMAgenerallydecreasewithanincreaseinpercentpassing4.75mmsieve.Hence,thecoarserthemix,thehigheristheVTMandVMA.ThedryroddedcoarseaggregateVCA(VCA
DRC)fallsbetweenthecompactedmixVCAvaluesforgradationswith
15%and25%passingthe4.75mmsieve.Thisindicatesthatstone-on-stonecontactbeginsatsomepointbetween25%and15%(approximatelyat22%)passingthe4.75mmsieve.
Table5.SummaryofMixVolumetricProperties
CompactedOGFCMixGradation(%passing4.75mmsieve)
AsphaltContent
TMD*VTM,%
VMA,%
VCA,%
VFA,%
15 5.55 2.47515.1 26.3 37.3 42.6
25 5.51 2.51214.3 24.5 43.3 41.7
30 5.48 2.51113.6 24.0 46.6 43.3
40 5.42 2.48712.5 23.9 54.1 47.3*TMD=TheoreticalmaximumdensityDryroddedVCA=41.7%.
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20
19
18
17
16
15
14
13
1211
10
0 5 10 15 20 25 30 35 40 45PercentPassing4.75mmSieve
Figure3.PercentPassing4.75mmSievevs.VoidsinTotalMix
Note:SamplesCompactedWith100GyrationsofSGC
55
VMA VCA50
45
40
35
30
2520
0 5 10 15 20 25 30 35 40 45
PercentPassing4.75mmSieve
Figure4.PercentPassing4.75mmSievevs.VMAandVCANote:Dry-RoddedVCA=41.7%
9
VoidsinTotal(MixVTM,%
)
Voids
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Also,theVMAcurvestartstocurlupward(VMAincreases)atabout30%passing4.75mm
sieve.ThereducedslopeinVMAindicatesstone-on-stonecontactisbeginningtobelost,andfurtherincreasesintheamountofthefineaggregatedonotbringtheaggregatesanycloser.HighVTMassociatedwiththecoarsergradationwillalsofacilitatebetterdrainageofwater.A
preliminary,crudetestcarriedoutbyholdingcompactedOGFCspecimensunderwatertapindicatedalmostfreeflowofwaterthroughthemixwith15%passingthe4.75mmsieve,moderateflowthroughmixwith25%passing4.75mmsieve,andverypoorornoflowthroughmixeswith30%and40%passingthe4.75mmsieve.
Draindown
Inhotmixasphalt,thecoarserthegradation,thegreateristhepotentialofdraindownofasphaltbinderduringstorageand/ortransportation.Draindowncausesdeficientbinderinpartofthemix(resultinginraveling)andexcessivebinderintheotherpartofthemixcausingbleedinglossofpermeability,andpotentialforflushingandrutting.DraindowntestswereconductedonuncompactedOGFCmixes(withPG64-22binder)at160Cand175CaccordingtotheNCAT
draindowntestmethod.TheSchellenbergdrainagetestusedinEuropeisconductedat175C(7).TheresultsofNCATdraindowntestareshowninTable6.Themaximumpermissibledraindownis0.3%.Asexpected,themixwith15%passing4.75mmsieveshowedthemaximumdraindown.Themixwith25%passing4.75mmsieveshowedadraindownoflessthan0.3%at175C.However,whentestedwithPG76-22binder,themixwith15percentpassingthe4.75mmsieve,showedsignificantlylessdraindown.Itshouldbenotedthatthetemperaturesusedfordraindowntestsinthisstudyaresignificantlyhigherthantypicalproductiontemperatures.OGFCmixescontainingpolymermodifiedbinderssuchasSBorSBSarecommonlyproducedat150C.Itisrecommendedtoconductthedraindowntestattheproposedmixingtemperature.Nonetheless,thetestdatainTable6givestherelativedraindownpotentialofdifferentmixes.
Table6.SummaryofDraindownTestResults
Draindown(%)Gradation(percentpassing
4.75mmsieve)
15
25
30
40
PG64-22
0.45
0.10
0.11
0.12
160C
PG76-22
0.05
PG64-22
1.27
0.25
0.24
0.19
175C
PG76-22
0.30
AbrasionTest
TheCantabroabrasiontestwasconductedonmixeswithdifferentpercentagesofmaterialpassingthe4.75mmsieve.First,theunagedsamplesweretested.Next,sampleswereagedandtestedforabrasionloss.TheresultsareshowninTable7.Thedatashowthatunderbothagedandunagedconditionstheabrasionlossincreasesasthemixismadecoarser,themixwith15%passing4.75mmsieveshowsthehighestabrasionloss.Although,themixwith15%passing4.75mmsievesatisfiestheCantabroabrasioncriteria(7)of20%maximumforunagedspecimensand30%maximumforagedspecimens,thelosscanbereducedfurtherbyusingamodifiedbinderandincreasingtheasphaltcontentbyuseoffibers.Thiswasinvestigatedinthesecondphaseofthestudyreportedlater.
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Table7.SummaryofAbrasionTestResults
Gradation(percentpassing4.75mmsieve)
1525
30
40
Loss,%(Unaged)
14.712.1
11.7
8.1
Loss,%(Aged)
29.319.6
17.2
15.5
Differenceduetoaging(%)
14.67.5
5.5
7.4
PermeabilityThepermeabilityofmixeswithdifferentpercentagesofmaterialpassingthe4.75mmsieveweretestedwithafallingheadpermeameter.ThecoefficientsofpermeabilityobtainedforthedifferentmixesareshowninTable8.Asexpected,themixeswithlowerpercentageofmaterial
passingthe4.75mmsieveshowhigherpermeability.Thereisasignificantincreaseinpermeabilitybetweenthemixwith30percentpassingthe4.75mmsieveandthemixwith15percentpassingthe4.75mmsieve.Forcomparison,coarsegradedSuperpavemixeshavebeenfoundtohavepermeabilityintherangeof1.5mperdayto8.8mperdaywithvoidsrangingfrom6.4to8.8percent(testedwiththeFloridaPermeabilityTestMethod)(6).
Table8.SummaryofPermeabilityData
Gradation(percentpassing4.75mmsieve)
15
25
30
40
Rutting
Permeability(coefficient,m/day)
117
8828
21
Ruttestswereconductedonthefourmixesatdesignasphaltcontents.TheAsphaltPavementAnalyzer(APA)wasusedtorutthemixesunderawheelloadof445N(100lb),andahosepressureof690kPa(100psi).Themixesweretestedat64C,sincethePGgradeoftheasphaltwasPG64-22.Table9showstheresultsofruttests.Therutdepthsat8,000cyclesdonotshowawiderange,nordoesitshowanyparticulartrendwithpercentpassingthe4.75mmsieve.However,alloftherutdepthsareverysmall,lessthan5mm,andareconsideredacceptable.
Table9.SummaryofRutData
Gradation(percentpassing4.75mmsieve)
15
25
30
40
RutDepthat8000cycles,mm
4.05
3.83
4.29
3.41
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PhaseTwo
Inthenextphaseofthelaboratorystudy,mixeswerepreparedwith15percentpassingthe4.75mmsieveand6.5percentasphaltcontentusingsixdifferentbinder/additivecombinations.Test
samplesforthesixmixeswerecompactedwiththeSGC,usingthenumberofgyrationsrequiredtoachieveairvoidsclosertothosefoundinthefieldatthetimeofconstruction(about18percent).
Astudywascarriedouttodeterminetherequirednumberofgyrations.Threesamplesofeach
mixwerecompactedwith100gyrationsoftheSGCand50blowsofMarshallhammer.Theairvoidsatdifferentgyrationswerecomparedtoairvoidsgenerallyfoundinthefieldandtheairvoidsofthesamplecompactedwith50blowsMarshall(Figure5).Itwasdeterminedthatabout50gyrationswiththeSGCand50blowswiththeMarshallhammerproduceabout18percentairvoidsgenerallyfoundinthefield.Themixeswerepreparedwithsixdifferenttypesofbinderasdescribedearlier:PG64-22,PG64-22-SBS,PG76-22-SB,PG64-22-CF,PG76-22-SB-SWandPG64-22-SW.Thesamplesweretestedforvolumetricproperties,draindown,aging,rutting,and
moisturesusceptibility.ThevolumetricpropertiesareshowninTable10.Resultsfromothertestsarediscussedinthefollowingparagraphs.
242220
181614
121086420
VoidsinSpecimenCompactedwith50BlowsofMarshallHammer
0 20 40 60 80 100 120
NumberGyrationsinSGC
Figure5.Gyrationsvs.VTMplot.
12
VoidsinTotalMix
VTM
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Table10.VolumetricPropertiesofMixesWithDifferentBinders(AverageValues)
Binder BulkSp. TMD VTM VMA VCAGr.
PG64-22 2.044 2.441 16.3 29.0 37.3PG64-22withcellulose 2.043 2.441 16.3 29.0 37.3
PG64-22withslagwool 2.071 2.441 15.2 28.1 37.3
PG64-22withSBS 2.026 2.441 17.0 29.6 37.3
PG76-22-SB 2.002 2.441 18.0 30.5 37.3
PG76-22withslagwool 2.046 2.441 16.2 28.9 37.3
DraindownTheaveragedraindownvaluesat157C(315F)areshowninTable11.Thetesttemperatures
werereducedinPhase2torepresentproductiontemperaturesgenerallyusedinthefield.ResultsfromamultiplecomparisontestarealsoshowninTable11.Theseresultsindicatewhetherthereisanysignificantdifferencebetweenthedifferentmeansandifthereis,providestherankingofthedifferentmixesbasedonthemeans.Table11indicatesthatthedraindownvaluesaresignificantlyhigherforallmixeswiththePG64-22andthePG76-22-SBandalsodonotmeetthecriteriaof0.3percentmaximum.ItseemsthatSBS,slagwool,andcellulosearemoreeffectiveinreducingthedraindownathighertemperatures.
Table11.ResultsofDraindownTestsFromMixesWithDifferentBinders
Draindownat157C(315F)
DuncanGrouping Mean(%) AsphaltBinder
A 1.3585 PG64-22
A 1.1845 PG76-22-SB
B 0.5405 PG64-22withSBS
B 0.1245 PG76-22-SBwithslagwool
B 0.0510 PG64-22withslagwool
B 0.0040 PG64-22withcellulose
AgingTestSamplesofmixespreparedwithdifferentbindersweretestedwiththeCantabroabrasiontesttodeterminetheeffectofaging.Allofthesampleswereagedat160Cfor168hours(7days).
Table12showsthetestvaluesandtheresultsofmultiplecomparisontest.TheresultsshowthatthemixeswithunmodifiedPG64-22binderhavethehighestabrasionloss,andthemixeswithPG76-22-SWhavethelowestabrasionloss,withtheothermixeshavingvaluesinbetween.Ingeneral,mixeswithPG64-22plusSBSandthePG76-22-SBbindersshowlessabrasionthanmixeswiththeotherbinders.Althoughallmixesmeetthemaximumlosscriteriaof30percent,itappearsthatthecombineduseofpolymermodifiedbinderandfiberwillminimizetheabrasionlossfromagingandthusincreasethedurabilityoftheOGFC.
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Table12.AbrasionLoss(AgedSamples)forMixesWithDifferentTypesofBinder
DuncanGrouping Mean(%) AsphaltBinder
A 26.2 PG64-22
B A 19.3 PG64-22withslagwool
B A 18.8 PG64-22withcellulose
B C 15.7 PG76-22-SB
B C 13.0 PG64-22withSBS
C 9.0 PG76-22withslagwool
RuttingTestRuttingtestswereconductedonsamplesofmixeswithdifferentbinderswiththeAPAusingidenticalproceduresasphase1.Table13showsthemeansandtheresultsofmultiple
comparisontest.TheresultsshowthatingeneralmixeswithPG76-22-SBbindershowlessruttingcomparedtomixeswithPG64-22binder.OfthemixeswithdifferentPG64-22binders,themixeswiththeunmodifiedbindershowedthehighestamountofrutting,whiletheonewithSBSshowedtheleastamountofrutting.ThelowestrutdepthwasobtainedincaseofSBmodifiedPG76-22withslagwool.Again,thecombineduseofapolymer-modifiedbinderandfiberresultedinthelowestrutdepth.
Table13.RutDepthforMixesWithDifferentTypesofBinder
DuncanGrouping Mean(%) AsphaltBinder
A 6.28 PG64-22
B A 5.24 PG64-22withcellulose
B C 5.00 PG64-22withslagwool
B C 4.70 PG64-22withSBSD C 3.81 PG76-22-SB
D 2.70 PG76-22withslagwool
MoistureSusceptibilityTestMoisturesusceptibilityofmixeswasevaluatedbyconductingtensilestrengthtestonconditioned(5freeze/thawcycles)andunconditionedcompactedsamples(airvoids71percent)ofmixeswithdifferentbinders.Thistestwasincludedinphase2toevaluatetheeffectofbindertypeandfibersonthemoisturesusceptibilityofOGFCmixes.Table14showstheaveragevaluesoftensilestrengthratiosobtainedforthedifferentmixes.TheresultsshowthatmixeswithPG64-22-SBSshowthehighestTSR(100percent),whereasthemixeswithunmodifiedPG64-22showthelowestTSR(below70percent).Ingeneral,allthemixes,exceptthosewithunmodifiedPG64-22andPG64-22-SWshowTSRvaluesgreaterthan80percent.Itappearsthatbothpolymer-modifiedbinderandfibershouldbeusedespeciallyinthenortherntierstatesoftheU.S.,whichexperiencecoldclimatesandfreeze/thawcycles.
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Table14.TSRValuesforMixesWithDifferentBinders
AsphaltBinder Mean(%)
PG64-22withSBS
PG76-22withslagwoolPG64-22withcellulosefiber
PG76-22-SB
PG64-22withslagwool
PG64-22
SUMMARYOFLABORATORYSTUDYThefollowingobservationscanbeobtainedfromthelaboratorystudy:
10098
91877562
1.Agradationwithnomorethanabout20percentpassingthe4.75mmsieveis
requiredtoachievestone-on-stonecontactconditionandprovideadequatepermeabilityinOGFCmixes.2.Mixeswith15percentaggregatespassingthe4.75mmsievearesusceptibleto
significantdraindownofthebinder.Therefore,itisnecessarytoprovideasuitablestabilizersuchasfiberinthemixtopreventexcessivedraindown.
3.AbrasionlossofOGFCmixesresultingfromagingcanbereducedsignificantlywiththeadditionofmodifiers.Inthisstudy,allofthemodifiedbindershadsignificantlylowerabrasionlossthantheunmodifiedbinder.Theuseofbothpolymer-modifiedbinderandfibercanminimizetheabrasionlossandthusincreasethedurabilityofOGFC.
4.Forthebindersusedinthisstudy,rutdepthsasmeasuredwiththeAPAdidnotvaryoverawiderange.However,withintherangeofrutvaluesobtained,themixeswithmodifiedbindershadsignificantlylessruttingthanmixeswithunmodifiedbinders.A
higherPGbindergradeseemstohaveagreatereffectinreducingruttingthanalowerPGbindergrade.Apolymer-modifiedasphaltwithfibergavetheleastamountofrutting.
5.Moisturesusceptibility,asmeasuredbyTSRvalues,islowerformixeswithmodifiedbindersthanmixeswithunmodifiedbinders.Allofthemodifiersexceptslagwool(withPG64-22)producedmixeswhichhadTSRvaluesinexcessof80percent.Again,bothpolymer-modifiedbinderandfibershouldbemosteffectiveespeciallyincoldclimateswithfreeze/thawcycles.
TentativeOGFCMixDesignProcedure
Thefollowingtentativemixdesignsystemisrecommendedforthenew-generationOGFCmixesonthebasisofthelaboratorystudy,observationofin-placeperformanceofOGFCmixesinGeorgia,andexperienceinEurope.Thesystemcanberefinedfurtherasmoreexperienceisgainedinthefuture.
Step1.MaterialsSelection
ThefirststepinthemixdesignprocessistoselectmaterialssuitableforOGFC.MaterialsneededforOGFCincludeaggregates,asphaltbinders,andadditives.Additivesincludeasphaltbindermodifiers,suchaspolymersandfibers.
GuidanceforsuitableaggregatescanbetakenfromrecommendationsforSMA(4).Thebinder
selectionshouldbebasedonfactorssuchasenvironment,traffic,andexpectedfunctionalperformanceofOGFC.Highstiffnessbinders,suchasPG76-xx,madewithpolymersare
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recommended(5)forhotclimatesorcoldclimateswithfreeze-thawcycles,mediumtohigh
volumetrafficconditions,andmixeswithhighairvoidcontents(inexcessof22percent).Theadditionoffiberisalsodesirableundersuchconditionsandalsohavebeenshowntosignificantlyreducedraindown.Forlowtomediumvolumetrafficconditions,eitherpolymer
modifiedbindersorfibersmaybesufficient.
Step2.SelectionofDesignGradation
BaseduponthislaboratorystudyandrecentexperiencesinGeorgia,thefollowingmastergradationbandisrecommended.
Sieve
19mm
12.5mm
9.5mm
4.75mm
2.36mm
0.075
mm
PercentPassing
100
85-10055-
7510-25
5-10
2-4
Selectionofthedesigngradationshouldentailblendingselectedaggregatestockpilestoproducethreetrialblends.Itissuggestedthatthethreetrialgradationsfallalongthecoarseandfinelimitsofthegradationrangealongwithonefallinginthemiddle.Foreachtrialgradation,determinethedry-roddedvoidsincoarseaggregateofthecoarseaggregatefraction(VCADRC).Coarseaggregateisdefinedastheaggregatefractionretainedonthe4.75mmsieve.
Foreachtrialgradation,compactspecimensatbetween6.0and6.5percentasphaltbinderusing50gyrationsofaSuperpavegyratorycompactor.Iffibersareaselectedmaterial,theyshouldbeincludedinthesetrialmixes.Determinethevoidsincoarseaggregate(VCA)foreachcompactedmix.IftheVCAofthecompactedmixisequaltoorlessthantheVCADRC,stone-on-stonecontactexists.Toselectthedesigngradation,chooseatrialgradationthathasstone-on-stonecontactcombinedwithhighvoidsintotalmix.
Step3.DetermineOptimumAsphaltContent
Usingtheselecteddesigngradation,prepareOGFCmixesatthreebindercontentsinincrementsof0.5percent.Conductdraindowntestonloosemixatatemperature15Chigherthananticipatedproductiontemperature.Compactmixusing50gyrationsofaSuperpavegyratory
compactoranddetermineairvoidcontents.ConducttheCantabroabrasiontestonunagedandaged(7days@60C)samples.RuttingtestswiththeAsphaltPavementAnalyzerandlaboratorypermeabilitytestingareoptional.Insufficientdatawasaccumulatedinthisstudytorecommendacriticalrutdepth.However,laboratorypermeabilityvaluesgreaterthan100m/dayarerecommended.Theasphaltcontentthatmeetsthefollowingcriteriaisselectedasoptimumasphaltcontent.
1.AirVoids.Aminimumof18percentisacceptable,althoughhighervaluesaremoredesirable.ThehighertheairvoidsarethemorepermeabletheOGFC.
2.AbrasionLossonUnagedSpecimens.TheabrasionlossfromtheCantabrotestshouldnotexceed20percent.
3.AbrasionLossonAgedSpecimens.TheabrasionlossfromtheCantabrotestshouldnotexceed30percent.
4.Draindown.Themaximumpermissibledraindownshouldnotexceed0.3percentby
totalmixturemass.
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Ifnoneofthebindercontentstestedmeetallfourcriteria,remedialactionwillbenecessary.Air
voidswithinOGFCarecontrolledbythebindercontent.Ifairvoidsaretoolow,theasphaltbindercontentshouldbereduced.Iftheabrasionlossonunagedspecimensisgreaterthan20percent,moreasphaltbinderisneeded.Abrasionlossvaluesofagedspecimensinexcessof30
percentcanberemediedbyeitherincreasingthebindercontentorchangingthetypeofbinderadditive.Ifdraindownvaluesareinexcessof0.3percent,theamountofbinderand/ortypeofbinderadditivecanbeadjusted.Fiberstabilizersaretypicallyincorporatedintothemixatarateof0.2to0.5%ofthetotalmix.
Step4.EvaluateMixforMoistureSusceptibility
ThemixdesignedwithStep1through3shouldbeevaluatedformoisturesusceptibilityusingthemodifiedLottmanmethod(AASHTOT283)withfivefreeze/thawcyclesinlieuofonecycle.Theretainedtensilestrength(TSR)shouldbeatleast80percent.
CONSTRUCTIONOFTESTSECTIONS
In1992,theGDOTinitiatedafieldstudytoevaluateOGFCmixes(5).TheprimaryobjectiveofthisstudywastocompareGDOTconventionalOGFCswithcoarserOGFCsmodifiedwithdifferentbinderadditivecombinations.Thiswasaccomplishedbyconstructingsixtestsectionsusingacoarsergradationwithsixcombinationsofpolymer/additiveonI-75southofAtlanta,Georgia.
ThesixtestsectionswerecharacterizedasacoarseOGFC(D),coarseOGFCwith16percent
crumbrubber(D16R),coarseOGFCwithcellulosefibers(DC),coarseOGFCwithmineralfibers(DM),coarseOGFCwithSBpolymer(DP),andcoarseOGFCwithSBpolymerandcellulosefibers(DCP).Mixdesignsforeachofthesemixeswasconductedusingthe"MethodofDeterminingOptimumAsphaltContentforOpen-GradedBituminousPavingMixtures,"whichisastandardprocedureforGDOT(GDT-114).
Job-mix-formula(JMF)dataforeachofthesixmixesarepresentedinTable15.Thistable
showsthatallsixOGFCmixeshadidenticalgradationsandonlydifferedbyrespectiveasphaltcontents.Ofinterest,theJMFgradationfallswithinthegradationbandrecommendedinthenewmixdesignsystem(Figure6).
Table15.LaboratoryTestResultsfortheSixOGFCMixes(6)
Test D D16R DM DC DP DCP
Percentpassing19.0mm 100 100 100 100 100 100
Percentpassing12.5mm 99 99 99 99 99 99
Percentpassing9.5mm 75 75 75 75 75 75
Percentpassing4.75mm 18 18 18 18 18 18Percentpassing2.36mm 8 8 8 8 8 8
Percentpassing0.075mm 2 2 2 2 2 2
PercentAsphaltBinderofTotalMix
%AC 6.0 6.6 6.3 6.4 6.2 6.4
OtherTestData
Cantabro(%Wear) 13.5 8.6 5.7 5.8 8.6 8.2
Drainage(%Loss) 0.37 0.05 0.06 0.06 0.34 0.04
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Figure6.GradationofOGFCFieldTestSections
TestsconductedinadditiontothemixdesignincludedtheCantabroabrasionandSchellenbergDrainagetests.ResultsoftheCantabroabrasiontestindicatedthatallsixoftheOGFCmixeswouldmeettherequirementof20percentlossmaximumrecommendedintheproposedmixdesignsystem.Infact,forthefivemixescontainingbinderadditives,abrasionlossvalueswerealllessthan9percent.ThoughtheSchellenbergDrainagetestisnotidenticaltothe
NCATdraindowntest(4),fourofthesixmixesmettypicalSchellenbergdrainagerequirementsof0.3percentbytotalbindermass.Ofthetwomixesnotmeetingthe0.3percentdraindown,oneusednopolymers/additives(D)andtheotherusedjustapolymer(DP).
Productionofthemixesinthefieldwasaccomplishedwithadouble-barreldrumplant.The
plantwasmodifiedslightlyinordertoincorporatethecrumbrubberandfibersintothemixingprocess.Duringproduction,trucksampleswereobtainedtodetermineasphaltcontent,gradation,airvoids,andCantabroabrasionlossvalues.Table16presentstheresultsofthistesting.
BasedonTable16,fiveoftheproducedmixeswerefinerthantheJMFgradationonthe4.75
mmsieve.Onlyonegradation(DM)didnotmeettherecommendedgradationbandwithinthe
newmixdesignprocedure.However,thismixonlyvariedfromthebandby1.2percentonthe9.5mmsieve.Asphaltcontentsrangedfrom5.9to6.4percent.Airvoidcontentsoflabcompactedsamplesusing25blowsperfaceofaMarshallhammerrangedfrom10.9to14.1percentandarelowerthanwouldbeanticipatedontheroadway.Cantabroabrasionlossvaluesrangedfrom7.0to15.7percentandarealllowerthanthesuggested20percentmaximumcriteria.
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Table16.LaboratoryTestResultsforFieldProducedOGFCMixes( 6)
SampleType JMF D DM DC DCP DP D16R
SieveSize,mm TotalPercentAggregatePassingbyWeight
19.0 100 100 100 100 100 100 100
12.5 99 98.3 98.9 96.7 97.0 99.1 96.3
9.5 75 70.0 76.2 64.0 68.6 69.9 60.3
4.75 18 21.0 23.9 19.0 19.1 23.1 15.7
2.36 8 8.7 9.0 7.7 7.8 8.4 7.4
0.075 2 3.6 3.1 2.8 2.4 3.1 2.6
MiscellaneousTestData
AsphaltContent Extracted 5.85 6.22 6.16 6.14 6.25 6.41
TMD --- 2.484 2.445 2.429 2.424 2.476 2.451
VTM --- 12.2 11.4 11.5 10.9 14.1 12.0
Cantabro(%Wear) --- 10.3 8.1 14.7 7.0 15.9 7.6
Inadditiontotestingtrucksamples,coreswereobtainedfromeachofthesixtestsections.Testingofthesesamplesincludedasphaltcontentsandgradationsbyextractionandairvoidcalculations.Anadditionaltestconductedwasthein-placepermeabilityofeachsection.ResultsofthistestingarepresentedinTable17.
Table17.LaboratoryTestResultsforRoadwayCoreSamplesfromOGFCTestSections
SampleNo. JMF D DM DC DCP DP D16R
SieveSize,mm TotalPercentAggregatePassingbyWeight19.0 100 100 100 100 100 100 100
12.5 99 99.3 98.6 99.2 97.6 99.3 99.2
9.5 75 77.3 77.2 75.5 73.1 76.5 76.7
4.75 18 28.1 28.3 28.0 26.9 27.8 28.0
2.36 8 13.1 13.6 13.7 13.0 13.1 13.1
0.075 2 3.8 4.1 3.5 3.9 3.8 3.4
MiscellaneousTestData
AsphaltContent Extracted 5.51 5.87 6.18 5.27 5.85 5.69
VTM --- 17.8 17.2 16.4 16.0 17.6 18.1
Permeability --- 46 82 71 71 84 67(m/day)
OfnoteinTable17arethein-placeairvoidcontentsofthecompactedmixes.Airvoidcontentsrangedfrom16.0to18.1percentwhichrelatewelltothedataaccumulatedinthelaboratorypartofthisstudy(Table10).Thesevaluesalsoseemtovalidatetheselectionof18percentairvoidsminimumduringthenewmixdesignsystemasmixesmeetingthegradationrequirementscanbeconstructedtohave18percentairvoids.Permeabilityvaluesobtainedfromthesixtestsectionsrangedfrom46to84m/dayandappeartocorrespondreasonablywellwithpermeabilitydatafromthelaboratoryworkinthisstudy(Table8).
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DataobtainedfromthisGDOTfieldstudyindicatethatOGFCmixesmeetingthegradation
requirementsoftherecommendedmixdesignprocedurecanbeproducedsuccessfullyinthefield.Also,becauseofthetestingproceduresusedbyGDOTintheirfieldstudy,itisbelievedthatthesixmixeswouldbesimilartoOGFCmixesdesignedusingthenewmixdesign
procedure.Therefore,theperformanceofthesemixesinthefieldshouldprovidevaluableinformationonhowmixesdesignedwiththenewprocedurewouldperform.
PERFORMANCEOFTESTSECTIONS
During1998(sixyearsafterconstruction),representativesofNCATperformedavisualdistresssurveyonthesixOGFCtestsections(8).Thesurveyconsistedofevaluatingeachsectionforsurfacetexture,rutting,cracking,andraveling.Duringthecourseofthesurvey,coreswereobtainedfromeachsectionandusedtodeterminethelaboratorypermeability.AlsoreportedinthissectionaretheresultsoffrictiontestingconductedbytheGDOT3.5yearsafterconstruction(5).
VisualDistressSurvey
SurfaceTexture
Allsixtestsectionshadexperiencedsomecoarseaggregatepopout.TheD16RsectionappearedtohavethemostwhiletheDC,DM,andDPsectionsallhadaverylowamount.Anothersurfacetextureitemwastheexistenceofsmallfatspotsonthepavementsurface.Eachofthesixsectionshadthesefatspots.However,nonewerelargerthanapproximately15cmdiameter.TheDandDCPappearedtohavethemostbutwerenotdeemedsignificant.
Rutting
Rutdepthmeasurementsweremadeforeachsectionusingastringline.Rutdepthsrangedfrom0.0mmfortheDPsectionto4.1mmfortheDCsection.Noneofthesectionswerecharacterizedashavingsignificantamountsofrutting.
Cracking
TheprimaryformofcrackingonallsixsectionswasreflectivefromaPortlandcementconcretepavementunderlyingeachsection.Table18presentsdescriptionsandpercentagesofreflectivecracksencountered.Percentagesweredeterminedbycountingthenumberoftransversecracksvisibleatthepavementsurface.
Table18.SeverityandPercentageofTransverseReflectiveCracks
Section
D
D16R
DMDC
DP
DCP
Description
Lowtomediumseverity
Lowtohighseverity
LowseverityLowseverity
Lowtomediumseverity
Lowtomediumseverity
%CracksShowing
75
87
5545
61
65
Table18showsthatfiveofthesixsectionshadlowtomediumseverityreflectivecracking.ThetwoOGFCmixescontainingonlyfibers(DMandDC)hadtheleastamount(andseverity)ofcrackingwhiletheD16Rsectionhadthehighestamountandseveritycracking.Reflectivelongitudinalcrackswerealsoobservedonfivesections.OnlytheDandD16Rsectionshadwhatcouldbecharacterizedasmediumseveritylongitudinalcracking.
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Besidesreflectivecracking,onlytheD16Rsectionshowedanyothertypeofcracking.
Secondarycrackingaroundsomereflectivecrackshadoccurred.
Raveling
Allsixsectionsshowedsomesignsofraveling.However,allravelingwasminimalexcepttheD16Rsectionwhichshowedsomemediumseverityravelingnexttosomecracks.
PermeabilityTestingofCores
Three150mmcoreswereobtainedfromeachofthesixsections.Table19presentstheaveragelaboratorypermeabilityvaluesfromeachsectionaswellasaveragein-placeairvoidcontents.Statistically,nosignificantdifferencesexistbetweenthepermeabilityvalues;however,theDCandDCPsectionsdidhavethehighestaveragepermeabilityat74and70m/day,respectively.In-placeairvoidcontentsrangedfrom15to19percent.Bulkspecificgravitymeasurementsweredeterminedbyvolumetricmeasurements.Itisinterestingthatthisrangeofairvoidcontentscorrespondwellwiththeroadwaycoreairvoidcontents(atthetimeofconstruction)presented
inTable17.Again,thisappearstoprovidevaliditytotheselectionof18percentairvoidsminimuminthenewmixdesignsystem.ThiscriteriaappearstoberelatedtoairvoidcontentsatbothconstructionandduringthelifeofanOGFCpavement.Additionally,itappearsthatthemixdesignprocedureusedbyGDOTinthisexperimentresultedinOGFCmixeswithstone-on-stonecontacteventhoughitwasnotspecificallytested.
Table19.AveragePermeabilityandIn-PlaceAirVoidContentsfortheSixTestSections
Section
D
D16R
DM
DCDP
DCP
FrictionTesting
Avg.Permeabilitym/day
25
38
28
7416
70
Avg.In-PlaceAirVoids,%
16.7
15.8
19.9
16.213.9
19.2
FrictiontestingwasconductedbyGDOT3.5yearsafterconstructionaccordingtoASTME274procedures(5).Resultsofthistestingindicatedthatfrictionvaluesforthesixsectionsrangedfrom49to51.Thesevaluesweredeemedsatisfactory(5).
CONCLUSIONS
ResultsofthisstudyshowedthatacoarsergradationforOGFCmixesprovidesabetterperformingOGFCpavement.Gradationsnear15%passingthe4.75mmsieveperformedmuchbetterthanfinergradationsinthelaboratory.Modifiers,whetherpolymerand/orfibers,werealsoshowntoenhancetheperformanceofOGFCmixes.Usingthisknowledge,anewmixdesignsystemforOGFCmixeswasrecommended.
ConstructionandperformancedataforsixOGFCpavementsthatwouldcloselyresemblemixes
resultingfromthenewmixdesignsystemwerealsodiscussed.Basedupontheinformationobtainedfromboththelaboratoryandfieldwork,itisconcludedthatthenew-generationOGFCwillprovideabetterperformingmixture.
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2.3.
4.
5.
6.
7.
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