EVALUATIONOFINTERNATIONALFRICTIONINDEXANDHIGHFRICTIONSURFACES
ThesissubmittedtothefacultyoftheVirginiaPolytechnicInstituteandStateUniversityinpartialfulfillmentoftherequirementsforthedegreeof
MasterofSciencein
CivilandEnvironmentalEngineering
JulioAlbertoRoa
COMMITTEEMEMBERS:
Dr.GerardoW.Flintsch,ChairDr.AntonioA.TraniDr.LinbingWang
DECEMBER5,2008Blacksburg,Virginia
Keywords:InternationalFrictionIndex,harmonization,high‐frictionsurface,safety,testingdevices.
ii
ABSTRACT
Statehighwayagencieshaveanobligationtoprovideuserswithoptimalsurface
conditionsundervariousweatherconditionsthroughouttheyear.Asatisfactory
pavementsurfaceshouldexhibitgoodfrictionandtexturedepthtoreduceroadway
highwayaccidents.Thisiswhyfrictionisstartingtoreceiveincreasedattentionin
thepavementmanagementprocess.
Therehavebeennumerousresearcheffortsbydifferentcountriesandagenciesto
betterunderstandthebehaviorofdifferentfrictiontestingdevicesandtheinfluence
oftexture,speed,andotherexternalconditionsontheirmeasurements.
Thefirstpartofthisthesispresentsaresearchefforttocompareandharmonize
textureandskidresistancemeasurementstakenwithvariousdeviceson24
pavementsectionswithawiderangeoftextures.Measurementswerecompared
andtheInternationalFrictionIndex(IFI)calculatedfollowingPIARCandASTM
steps.
TheresultsrevealeddiscrepanciesintheIFIvaluescalculatedforthedifferent
devices,suggestingthatthecoefficientsA,B,andCproposedbyPIARCmayneedto
beadjustedforeachdeviceconsideredbeforetheIFIcanbeimplementedbythe
surfacepropertiesconsortiumparticipatingagencies.InthisresearchtheA,B,andC
coefficientswerethenrecalculated,andthepredictedvaluesoffrictionusingthese
revisedcoefficientsarepresented.Thecoefficientsdevelopedwerealsousedto
obtainIFIvaluesforhigh‐frictionsurfaces(HFS).
Ithasbeenfoundthatunderdifferentconditions,differentparametersand
coefficientswillresult.Itisstronglyrecommendedequipmentcomparison
iii
experiments(liketheNASAandSmartRoadprograms)continuetobetter
determinethecoefficientsnecessaryforharmonization.
HFShaveemergedasviablehigh‐frictionpavementalternativesthatmitigatethe
consequencesofdrivererror,poorgeometricalignmentoftheroadway,and
insufficientfrictionatthetire‐pavementinteraction,especiallyduringwetweather.
ThisthesispresentsastudyoftheHFSavailableintheU.S.marketandtheir
performance(frictionandtexture)indifferentapplications,underdifferentweather
conditions,andinvariouslocations.Thisthesisalsopresentstheresultsofthe
benefit‐costanalysisforthestudiedHFS.
iv
ACKNOWLEDGEMENTS
IwouldliketothankGodforgivingmetheopportunitytostudyinsuchagreat
schoolwithwonderfulprofessorsandcolleagues.
Iwouldalsoliketoexpressmydeepestgratitudetomyparents,mybrother,my
sister,andmyunclesandaunts,whohaveallbeenthereformeinthisprocesswith
wordsofencouragement,support,prayers,andfinancialsupport.
Iwouldliketorecognizemyprofessorsandmentorsfortheinvaluablehelpand
guidancethroughmystudies.
Thankyou,Dr.Flintsch,fortheeverydaylessons,unconditionalhelp,patience,and
fortheprivilegeofworkingwithsuchanoutstandingprofessionallikeyou.
Thankyou,Dr.Trani,forbelievinginmeandbeingmymentor,friend,andsomeone
Ideeplyadmireandrespect.
Thankyou,Dr.Wangforyourguidanceandhelpthroughthisprocess.
Thankyou,Dr.Edgarforyoursincerefriendshipandforalwaysbeingavailableto
teach,explain,guide,andhelpthroughouttheprocessofthisthesis.
ThankyoutoallthepeoplefromtheFederalHighwayAdministration(FHWA)and
theConnecticut,Minnesota,Pennsylvania,SouthCarolina,Wisconsin,andVirginia
departmentsoftransportation(DOTs)andtoKevinMcGheefromtheVirginia
TransportationResearchCouncil.
v
IalsowanttothankmyRepublicaDominicanaforgivingmethedesireandpassion
toworkhard,accomplishgreatthings,andmakeadifference.
FinallythisthesisisdedicatedtomyfriendsinBlacksburgandintheDominican
Republicwhohavebeenpartofthis:Manuel,Henry,Oscar,Mario,Billy,Dana,and
theCranwells.
Thisthesisispossibleonlybecauseofthecombinationofeffortsandsupport
providedbyyouall.
GRACIAS DE TODO CORAZON
vi
TABLEOFCONTENTS
ABSTRACT........................................................................................................................ ii
ACKNOWLEDGEMENTS............................................................................................... iv
LIST OF TABLES............................................................................................................. ix
LIST OF FIGURES ............................................................................................................ x
CHAPTER I Introduction ................................................................................................. 1
1. Background................................................................................................................. 22. Problem Statement...................................................................................................... 23. Objectives ................................................................................................................... 34. Organization of the Thesis.......................................................................................... 4
Chapter 2: Evaluation of the International Friction Index .......................................... 4Chapter 3: Field Performance of High-Friction Surfaces ........................................... 4Chapter 4: Findings, Conclusions, and Recommendations ........................................ 4
5. Significance ................................................................................................................ 5CHAPTER II Evaluation of The International Friction Index Coefficients ...................... 6
ABSTRACT.................................................................................................................... 61. INTRODUCTION ...................................................................................................... 72. OBJECTIVE ............................................................................................................... 73. BACKGROUND ........................................................................................................ 8
3.1 Harmonization Effort ............................................................................................ 83.3.1 PIARC Experiment to Compare and Harmonize Texture and Skid Resistance Measurements ....................................................................................... 83.1.2 NASA Wallops Friction Workshops Program............................................. 103.1.3 HERMES Experiment.................................................................................. 10
4. DATA COLLECTION ............................................................................................. 115. RESULTS AND ANALYSIS................................................................................... 14
5.1 Changes of Friction with Speed.......................................................................... 145.2 IFI Comparisons.................................................................................................. 155.3 Speed Parameter Calculation .............................................................................. 20
6. FINDINGS AND RECOMMENDATIONS ............................................................ 237. ACKNOWLEDGEMENTS...................................................................................... 248. REFERENCES ......................................................................................................... 25
CHAPTER III FIELD PERFORMANCE OF HIGH-FRICTION SURFACES ............ 26
vii
ABSTRACT.................................................................................................................. 261. INTRODUCTION .................................................................................................... 272. OBJECTIVE ............................................................................................................. 283. BACKGROUND ...................................................................................................... 29
3.1 High-Friction Surfaces Application Processes ................................................... 303.2 High-Friction Surface Binders............................................................................ 303.3 Properties of Aggregates for High-Friction Surfaces ......................................... 31
3.3.1 Standard Practice for the Accelerated Polishing of Aggregates Using the British Wheel (AASHTO T279, ASTM D3319).................................................. 313.3.2 Resistance to Degradation and Abrasion (AASHTO T96, ASTM C131) ... 323.3.3 Soundness of Aggregates by Freeze-Thawing (AASHTO T103-91, ASTM C88)....................................................................................................................... 32
3.4 High-Friction Surfaces Aggregates..................................................................... 333.4.1 Calcined Bauxite.......................................................................................... 333.4.2 Dolomite ...................................................................................................... 343.4.3 Granite.......................................................................................................... 343.4.4 Silica ............................................................................................................ 343.4.5 Steel Slag ..................................................................................................... 35
3.5 Previous High-Friction Surfaces Studies ............................................................ 353.5.1 Investigative Study of the Italgrip System – Noise Analysis ...................... 353.5.2 Trials of High-Friction Surfaces for Highways ........................................... 363.5.3 Evaluation of Cargill Safelane Epoxy Overlay............................................ 363.5.4 Performance of Poly-Carb, Inc. Flexogrid Bridge Overlay System ............ 373.5.5 Florida DOT - Tyregrip Forensic Report..................................................... 373.5.6 Evaluation of Innovative Safety Treatments................................................ 373.5.7 Investigative Study of Italgrip System 2008................................................ 38
3.6 High-Friction Surface Systems Studied.............................................................. 383.6.1 Crafco HFS .................................................................................................. 383.6.2 Safelane (Cargill) ......................................................................................... 393.6.3 Tyregrip (Prismo - Ennis Paint)................................................................... 393.6.4 Italgrip.......................................................................................................... 403.6.5 FlexoGrid (Polycarb) ................................................................................... 40
3.7 High Friction Surfaces Typical Application Procedure...................................... 403.8 High-Friction Surface Potential Sources of Failures .......................................... 42
3.8.1 Epoxy Preparation - Composition................................................................ 423.8.2 Epoxy Aggregate Placement........................................................................ 433.8.3 Existing Pavement - Existing Asphalt Compatibility .................................. 433.8.4 Humidity and Moisture (Surface and Aggregate)........................................ 433.8.5 Ambient Temperature .................................................................................. 443.8.6 Curing Time................................................................................................. 44
3.9 High-Friction Surfaces Field Evaluations........................................................... 444. DATA COLLECTION ............................................................................................. 46
4.1 Location of Studied High-Friction Surfaces ....................................................... 464.2 Measurements of Friction and Texture Properties.............................................. 48
4.2.1 DF TESTER (ASTM E1969)....................................................................... 49
viii
4.2.2 CT METER (ASTM E2157)........................................................................ 494.2.3 GRIPTESTER (ASTM E1844).................................................................... 494.2.4 LOCKED WHEEL DEVICE (ASTM E274) .............................................. 50
4.3 Cost Data............................................................................................................. 514.4 Accident Data...................................................................................................... 52
5. RESULTS ................................................................................................................. 525.1 Friction and Texture Data Processing................................................................. 525.2 Initial Friction – Cost .......................................................................................... 56
6. ANALYSIS............................................................................................................... 566.1 Economic Analysis ............................................................................................. 56
6.1.1 Estimated High-Friction Surface Service Lives .......................................... 576.1.2 Values for Transportation Economic Study................................................. 586.1.3 Benefit-Cost ................................................................................................. 59
6.2 International Friction Index for High-Friction Surfaces. .................................... 627. FINDINGS AND RECOMMENDATIONS ............................................................ 638. ACKNOWLEDGEMENTS...................................................................................... 639. REFERENCES ......................................................................................................... 64
CHAPTER IV SUMMARY, FINDINGS, CONCLUSIONS, AND
RECOMMENDATIONS.................................................................................................. 67
1. FINDINGS................................................................................................................ 672. CONCLUSIONS ...................................................................................................... 683. RECOMMENDATIONS FOR FUTURE RESEARCH........................................... 69
ix
LISTOFTABLES
TABLE 1. Summary of IFI’s friction component values for different equipment.......... 17
TABLE 2. Summary of F60 IFI coefficients for different friction units ......................... 19
TABLE 3. Experimental and Calculated Sp Values......................................................... 21
TABLE 4. Coefficients a and b......................................................................................... 23
TABLE 1. Type of Aggregate and Price for Selected HFS.............................................. 33
TABLE 2. HFS Products Installed in the United States ................................................... 45
TABLE 3. HFS Locations Investigated ............................................................................ 46
TABLE 4. Type of Aggregate and Price for Selected HFS............................................. 51
TABLE 5. Crash Values for Economic Study .................................................................. 51
TABLE 6. Friction Measurements for Selected HFS ....................................................... 53
TABLE 7. Friction Texture Measurements for Selected HFS.......................................... 54
TABLE 8. Price and Initial Friction and Macrotexture for Selected HFS........................ 56
TABLE 9. Benefit-Cost Analysis for HFS Locations in Waukesha, Wisconsin.............. 60
TABLE 10. Benefit-Cost Analysis for HFS Locations in LaCrosse, Wisconsin ............. 61
TABLE 12. HFS Friction Measurements using the International Friction Index............. 62
x
LISTOFFIGURES
FIGURE 1. Friction and macrotexture testing equipment ............................................... 13
FIGURE 2. Sample of pavement surfaces available at the Virginia Smart Road............ 14
FIGURE 3. IFI F60 values for different equipment versus DFT F60 values .................. 18
FIGURE 4. Comparison of original and revised F60 values using three-parameter (A, B,
C) models. ................................................................................................................. 20
FIGURE 5. Comparison of computed and experimental Sp values ................................. 22
FIGURE 1. High-friction surface application (Adam and Gansen 2001). ....................... 42
FIGURE 2. High-Friction Surface Raveling (Adam and Gansen 2001) .......................... 44
FIGURE 3. HFS Locations investigated........................................................................... 47
FIGURE 4. Data collection devices.................................................................................. 48
FIGURE 5. Texture and friction whisker box plot for all HFS systems........................... 55
FIGURE 6. HFS wear and scuffing rate. .......................................................................... 58
1
CHAPTERI
INTRODUCTION
Highwayaccidentsarealeadingcauseofdeathandinjuryaroundtheworld.Each
year3.2millionpeopleareinjuredordisabledintheUnitedStatesasaresultof
roadcrashes(N.T.S.1999).Theseaccidentsnotonlycreateanenormoussocialcost
forindividual,families,andcommunitiesbutalsoplaceaheavyburdenonhealth
servicesandeconomies.
IntheUnitedStatesonepersondiesevery12minutesinamotorvehiclecrash
(N.T.S.1999).ThisstaggeringsituationhasledtheFederalHighwayAdministration
(FHWA)todeclaresafetyasoneofitstoppriorities.Wet‐weathercrashesandrun‐
off‐roadincidentsarethetwotypesofhighwayaccidentsresponsibleforthe
majorityofincidents;about25percentofallcrashesand14percentofallfatal
crashesoccuronwetpavementwhile59percentofhighwayfatalitiesoccurwhena
vehicleleavesitslane(JulianandMoler2008).Itisforthisreasonthathigh‐friction
surfaces(HFS)arestartingtobeconsideredforroadwayareaswhereadditional
frictionisneeded.HFShavetheabilityofincreasingfrictionandtexturebyutilizing
non‐polishable,roughaggregates.Differenttypesofbindersareusedtoholdthe
aggregateparticlestogetherandgluedtotheroadsurface.
Statedepartmentsoftransportationstrivetoprovideuserswithsmooth‐riding,safe
surfaceconditionsthroughouttheyear.Todoso,agenciesperiodicallymonitorthe
pavementsurfaceproperties.Themeasurementstakenareusedtodevelopsurface
restorationalternatives,newconstructionspecifications,accidentinvestigations,
pavementmanagementsystemsnetworksurveys,andwinterroadmaintenance.In
particular,agenciesusedifferentdevices,systems,andmethodstomeasurefriction
andsurfacetexture.Thisemphasizestheneedforfrictionmeasurements
harmonizationtoprovidecomparablefrictionmeasurementsamongdifferent
devices(Wamboldetal.1995).
2
1.BACKGROUND
High‐frictionsurfaces,orHFS,arespecialsurfacetreatmentsthatutilizeanon‐
polishableaggregateandaresin‐basedbindertoholdtheaggregatetotheroad
surface.Thistechnologywasoriginatedinthe1950swhentheU.K.government’s
TransportandRoadResearchLaboratory(TRRL)begantotesthardaggregateswith
variousbinderstoproduceextremelyhigh‐frictionsurfaces(Nicholls1998).Inthe
late1980sresearchersintheUnitedStatesbegantoinvestigatetheeffectivenessof
thesesurfacingsystemstoreducecrashesonblackspots.In1989astudyforthe
FederalHighwayAdministration(FHWA)donebyUniversityofMichiganon15
rampsat11interchangesin5statesfoundthatsurfacepropertieswererelatedto
truckcrashes,alongwithgeometryandvehicledynamics(JulianandMoler2008).
Inadditiontherehavebeennumerousresearcheffortsbydifferentorganizationsto
betterunderstandthebehaviorofdifferentfrictiontestingdevicesandtheinfluence
oftexture,speed,andotherexternalconditionsontheirmeasurements.These
effortsincludethePIARCExperimenttoCompareandHarmonizeTextureandSkid
ResistanceMeasurements,theNASAWallopsFrictionWorkshops,andtheHERMES
Experiment.
2.PROBLEMSTATEMENT
ThemainobjectiveofthisthesisistostudysomeoftheHFSsystemsavailableinthe
U.S.marketbymeasuringtheirperformanceindifferentapplications,under
differentweatherconditions,andinvariouslocations(states).Theresultsobtained
inthisresearchwillinformagenciesabouttheHFSavailableintheUnitedStates
andwillprovideapracticaltooltoestimatetheexpectedincreaseinskidresistance,
theexpectedservicelife,andthecostforeachavailableproduct.
3
Asecondaryobjectiveofthisthesisistocomparefrictionmeasureresultsfor
differentsurfaces,includingHFS,andshowifthepreviouslyadoptedmodelsfor
normalizingthesemeasurementsarevalid.Thecalibratedmodelsshouldpresent
theresultingmeasurementsinauniversalscale.
3.OBJECTIVES
ThemaingoalofthisthesisistostudysomeoftheHigh‐frictionsurfacesavailablein
theUnitedStatesmarket;bymeasuringtheirperformanceondifferentapplications,
underdifferentweatherconditions,andinvariouslocations(states).Thankstothe
resultsobtainedinthisresearch,agencieswillbeinformedonthehigh–friction
surfacesavailableonUnitedStates,andapracticaltooltoestimatetheexpected
increaseonskid,theexpectedservicelife,andthecostforeachavailableproduct.
Asecondarygoalistocomparefriction‐measuringresultsondifferentsurfaces
includinghigh‐frictionsurfacesandshowifthepreviouslyadoptedmodelsto
normalizethesemeasurementsarevalid.Thecalibratedmodelsshouldallow
presentingtheresultingmeasurementsinauniversalscale.
Thespecificobjectivesdefinedtoaccomplishthesegoalsarethefollowing:
• Comparefrictionmeasuringresultsmadewithdifferentdevices.
• Evaluateifavailableharmonizationadoptedmodelsarevalid.
• Investigatethehigh‐frictionsurfacesintheU.S.market
• Measuretheirperformanceindifferentapplications.
• Compiletheresultsobtainedinapracticaltooltosupportdecision‐making.
4
4.ORGANIZATIONOFTHETHESIS
ComplyingwiththeVirginiaTech’sgraduateschoolguidelinesthatencourage
publicationofresearchresults,thisthesisfollowsamanuscriptformatthatincludes
twomanuscripts.Eachmanuscriptisusedasanindividualchapterofthethesis.
Togethertheyrepresenttheresearchworkinwhichtheauthorwasinvolvedat
VirginiaTechduringthedurationofthemasterstudies.Thefirstchapterofthe
thesisisthisintroduction,whichprovidesanoutlinefortherestofthedocument.
Chapter2:EvaluationoftheInternationalFrictionIndex
Thisevaluationcomparesfrictionmeasurementsobtainedwithdifferentdevices
andevaluatesifthepreviouslyadoptedfrictionharmonizationmodelsarevalid.
Thechaptercomparesmacrotextureandskidresistancemeasurementstakenatthe
VirginiaSmartRoadin2008andprovidesgroundworkfortheharmonizationof
frictionmeasurementstakenondifferentHFSwithvariousdevices.Thispaperis
scheduledforpresentationatthe88thannualmeetingoftheTransportation
ResearchBoardandhasbeenrecommendedforpublicationintheJournalofthe
TransportationResearchBoard.
Chapter3:FieldPerformanceofHighFrictionSurfaces
ThischapterpresentsacriticalreviewoftheliteratureonHFSbinders,aggregates,
applicationprocesses,HFSwearrate,savedlives,andtheHFSavailableinthe
UnitedStates.ItalsocontainsexpectedinitialfrictionforHFSsystemsandasample
benefit‐costanalysisforanapplicationtestedinWisconsin.
Chapter4:Findings,Conclusions,andRecommendations
Thischapterpresentsasummaryoftheconcludingideasthatresultfromthe
researchpresentedinChapters2and3andgivesrecommendationsforfuture
researchintheseareasofstudy.
5
5.SIGNIFICANCE
Surfacepropertiesofroadsandrunwaysplayanimportantroleinroadandairport
safety.Roadandrunwaysurfacesmustprovideadequatelevelsoffrictionand
textureforthevehiclestravelingonthem.Thepurposeofthisthesisisto compare
frictionmeasureresultsondifferentsurfaces,includingHFS,andshowifthe
previouslyadoptedmodelsfornormalizingthesemeasurementsarevalid. The
resultsconcerningthevalidityofnormalizingmodelsareinvaluableforachieving
consistentpavementmanagementpracticesacrossnationalboundaries.Theyalso
contributetothestandardizationofspecificationsforpavingmaterials,highway
design,andrunwaydesign.
ThisresearchproducednewInternationalFrictionIndexcoefficientstocompare
andharmonizetextureandskidresistancemeasurementstakenwithdifferent
devicesandappliedthesecoefficientstothestudiedHFSsurfacestocompare
calculatedfrictiontomeasuredfriction.
Thisthesisprovidesagencieswithdetailedinformationonfrictionandtexture
performanceoftheHFSavailableintheUnitedStates.Inadditionitpresentsthe
methodologyandsampledatanecessarytoperformbenefit‐costanalysisforsome
oftheavailableHFS,anditpresentsthedurability,performance,andcostofthese
treatmentsinapracticalandaccessibleguideline.
6
CHAPTERII
EVALUATIONOFTHEINTERNATIONALFRICTION
INDEXCOEFFICIENTS
ABSTRACT
Thispaperpresentsaresearchefforttocompareandharmonizetextureandskid
resistancemeasurementstakenwithvariousdevicesattheVirginiaSmartRoadin
May2008bythemembersoftheVirginiaConsortiumforPavementSurface
Properties.
Therehavebeennumerouseffortsbydifferentcountriesandagenciestobetter
understandtherelationshipandbehaviorofdifferentfrictiontestingdevicesand
theinfluenceoftexture,speed,andotherexternalconditionsonthese
measurements.Measurementsobtainedwithdifferenttypesofequipmenton24
pavementsectionswithawiderangeoftextureswerecompared,andthe
relationshipbetweenfrictionandspeedforthedifferentpavementsectionsand
deviceswasstudied.Datawascollectedusingtwolocked‐wheelskidtrailers,a
GriptesterandaDynamicFrictionTester(DFT).Nineasphaltsectionsweretested;
sixareSUPERPAVEmixes,twoareStoneMatrixAsphaltandoneisanOpenGraded
FrictionCoarse.TheconcretesectionstestedincludedoneContinuouslyReinforced
ConcretePavementwithtinedfinishingandtwoepoxyoverlays.
Eventhoughallofthestepsincludedinthespecificationsderivedfromthe
experimentsbythePermanentInternationalAssociationofRoadCongresses
(PIARC)werefollowed,theresultsobtainedarenotsatisfactory.Fromatheoretical
stand‐pointallthevaluescomputedwiththeInternationalFrictionIndex(IFI)F60
7
shouldbeequal,butthisisnotthecase.DiscrepanciesintheIFIvaluescalculated
forthedifferentdevicessuggestthattheoriginalcoefficientsdeterminedduringthe
PIARCexperimentmayneedtobeadjustedforthedevicesevaluatedbeforetheIFI
canbeimplementedbytheparticipatingagencies.
1.INTRODUCTION
Asatisfactorypavementsurfaceshouldexhibitgoodqualitiesintermsoffriction,
smoothness,durability,lightreflection,tire‐pavementnoise,splash/spray,and
rollingresistanceinordertoprovidethedriverasafeandcomfortableride.Ofall
thefactors,frictionand/ortexturedepthofthesurfaceisparamounttocontrolling
andreducinghighwayaccidents.Thisiswhyfrictionisstartingtoreceiveincreased
attentioninthepavementmanagementprocess.StateHighwayAgencieshavean
obligationtoprovideuserswithoptimalsurfaceconditionsthroughouttheyear.To
doso,agenciesmustperiodicallymonitorthesurfaceproperties.The
measurementstakencouldbeusedtodevelopspecificationsforsurfacerestoration,
specificationsfornewconstructions,accidentinvestigations,networksurveysfor
pavementmanagementsystems,andmeasurementsforwinterroadmaintenance.
Therearedifferentdevicesusedbystatehighwayagenciestomeasurefriction.
Evenwhentakenbythesametypeofequipment,frictionmeasurementsarenot
consistentandthereforesometimescannotbecompared.Thisphenomenon
emphasizestheneedforharmonizationinordertoprovidecomparablefriction
surfacesfromonedevicetoanotherorfromstatetostate.
2.OBJECTIVE
Differentresearcheffortshavestudiedprocedurestonormalizesurface
measurementsmadebydifferenttypesoffrictionmeasuringequipment.The
objectiveofthispaperistocomparefrictionmeasuringresultsandshowifthe
previouslyadoptedmodelsarevalid.Theresearcheffortisaimedatcomparingand
8
harmonizingtextureandskidresistancemeasurementstakenattheVirginiaSmart
Roadin2008bythemembersofthePavementSurfacePropertiesConsortium.This
consortiumisajointeffortbytheFederalHighwayAdministration(FHWA)andthe
Connecticut,Georgia,Mississippi,Pennsylvania,SouthCarolina,andVirginia
departmentsoftransportation(DOTs).
3.BACKGROUND
3.1HarmonizationEffort
Therehavebeennumerouseffortsbydifferentorganizationstobetterunderstand
therelationshipandbehaviorofdifferentfrictiontestingdevicesandtheinfluence
oftexture,speed,andotherexternalconditionsontheirmeasurements.Someof
themaresummarizedfollowing.
3.3.1PIARCExperimenttoCompareandHarmonizeTextureandSkidResistance
Measurements
ThePermanentInternationalAssociationofRoadCongresses(PIARC)conducteda
seriesofexperimentstocomparetextureandfrictionmeasurements.Thefirstone
wasin1992whenPIARCundertookanexperimentthatencompassed16countries,
47measuringsystems,and54siteswiththeintentionofcomparingand
harmonizingtextureandskidresistancemeasurements.Underthiseffortawide
varietyofsurfacesweretestedandfrictionwasmeasuredwithfixed‐slip,side‐force,
andlocked‐wheeledsystemsatvariousspeeds.Texturewasmeasuredbystationary
andmobileequipment.
Aseriesofrelationshipsweredevelopedfromthecomparisonsofthe
measurements,whichproducedacommonharmonizedindexcalledthe
InternationalFrictionIndex(IFI)(Wamboldetal.1995).ThePIARCmodel,asitis
latercalled,incorporatedmacrotexturemeasurementswithside‐force,fixed‐slip,
andlocked‐wheelfrictionmeasurements,torecognizethepreviouslyidentified
dependenceoffrictiononspeedandtexture.
9
Macrotexturemeasurementswerefoundtobeexcellentpredictorsofthespeed
constantgradientneededtostandardizethefrictionmeasurementsusingtheIFI.
Textureclassificationswereproposedandaproceduretoestimatemacrotexture
fromtheprofiledatawasincorporatedintotheIFItoestimatetheMeanProfile
Depth(MPD).TheIFIcanthenbecalculatedfromtheresultsoffrictionvaluesand
speedconstant(Wamboldetal.1995).
TheIFIisamethodtoevaluateincommonscaledifferentmeasurementsproduced
bydifferentdevices.Thisindexconsistsoftwoparameters:thespeedconstant(Sp),
predictedthroughthemacrotexturemeasurements,andtheharmonizedfrictionat
60km/h(F60)(Wamboldetal.1995;Henry2000).
TheIFIcalculationfollowsthreesteps:
1) EstimatethespeedgradientcoefficientSp,usingthemeasuredmacrotexture:
Sp=a+b∗TX (1)
where
TX=macrotexturemeasurement(mm)
a,b=constantsfordifferentmethods/devicesused
2) ObtainthefrictionmeasurementfromthespecifiedslipspeedSforthefriction
instrumentusedatthestandardspeed,setat(60km/h):
(2)
where
FR(60)=Adjustedvalueoffriction
FR(S)=FrictionvalueatrecommendedslipspeedSfordevicesused
S=Recommendedslipspeedforeachdevice[km/h]
10
3) CalculatetheIFIfrictionnumberF(60)orgoldenstandardestimate,usingthe
coefficientsdevelopedbyPIARCforeachdevice:
F(60)=A+B∗FR(60)+C∗TX (3)
where
A,B,C=calibrationconstantsfortheselectedfrictionmeasuringdevice
TX=macrotexturemeasurement(mm)
3.1.2NASAWallopsFrictionWorkshopsProgram
TheNASAWallopsFrictionWorkshopshavebeenamulti‐yearprogramwhere
texture,friction,androughnessdatahasbeencollectedthroughvariousdevices,
someofwhichwerealsousedforthePIARCExperimentin1992.Measurements
aretakenatdifferentspeedsandalldevicesareoperatedaccordingtothe
manufacturer’sprocedures(Wamboldetal.2004).
Forself‐wettingfrictiondevices,runsaremadeconsecutively,andsome
nonstandardrunsareperformed,withvariationsonwaterfilmthickness,tiretypes,
inflationpressures,slipspeeds,andnormalloads.
3.1.3HERMESExperiment
In2001‐2002theHERMESprojectwasformedwiththeobjectiveofanalyzingthe
resultsoffieldtrialsinordertooptimizetheproceduresandprecisionofcalibrating
methodspreviouslydeveloped.Thisprojectconsidered15testingdevices,7
texturemeasuringdevices,and61testsurfacesinfivecountries(Descornet2004).
Ninecomparisonmeetingswereruninthefivemembercountries—Belgium,the
Netherlands,Spain,GreatBritain,andFrance—onawiderangeofsurfacescovering
mostmaterialsandtexturesavailableinEurope.Therewerethreemeetingsinthe
fallof2001,threeinthespringof2002,andthreeinthefallof2002.
11
Someofthefindingsforthisprojectstatethatusingthepowerlawforconstant
speedversusmeanprofiledepthbetterfitsthedata.Thisprocedurealsoconcludes
thatregardingconsistencytheEuropeanFrictionIndexworkssatisfactorily
nevertheless,regardingprecisionitishardlyacceptable.
4.DATACOLLECTION
In2006,theVirginiaTransportationResearchCouncil(VTRC)andtheVirginiaTech
TransportationInstitute(VTTI),initiatedaregionalpooled‐fundprojectknownas
thePavementSurfacePropertiesConsortiumtoestablisharesearchprogram
focusedonenhancingthelevelofserviceprovidedbytheroadwaytransportation
systembyoptimizingpavementsurfacetexturecharacteristics.Theprogramwas
setupwithsupportfromtheFHWAandnowincludessixDOTsfromthestatesof
Connecticut,Georgia,Mississippi,Pennsylvania,SouthCarolina,andVirginia.
Establishedasafive‐yearprogram,theconsortiumispartoftheactivitiesofthe
VirginiaSustainablePavementResearchConsortium(VA‐SPRC)andismanagedby
VTRCandrunbytheCenterforSustainableTransportationInfrastructureatVTTI.
Everyyearsinceitsinceptiontwoyearsago,alloftheparticipantmembersmeetfor
oneweekinMayattheVirginiaSmartRoadatVTTIwiththegoalofcomparingand
verifyingsurfacepropertymeasurementsonthesurfacesavailableatthefacility
witheachofthemember’sdifferentdevices.ThiseventistermedtheSurface
PropertiesRodeo,whichisacollaborativeresearcheffortoftheConsortiumthat
helpstheparticipantorganizationsverifytheoperation,reliability,andaccuracyof
theequipmentusedforpavementevaluationsandroadconstructionqualitycontrol.
Themay2008frictiontestingincludedtwolocked‐wheelskidtrailers,aGriptester
andadynamicfrictiontester(DFT).Oneofthelocked‐wheeltrailers(LWS1)used
onlyasmoothtire(ASTME‐524)whiletheothertrailer(LWS2)testedthesections
twice,oncewiththesmoothtireandthenwiththeribbedtire(LWR1)(ASTME‐
12
501).ThetestingwasconductedinaccordancewithASTME‐274(HenryandSiato
1983).TestingdonewiththeGriptesterutilizedthetesttiresuitableforthisfixed‐
slipdeviceinaccordancewith(ASTME1844)(Wamboldetal.2006).The
macrotexturedatawascollectedwithacirculartexturemeter(CTmeter)(Flintsch
etal.2003)inaccordancewithASTME2157.Figure1showspicturesofsomeofthe
participantdevices.
TheVirginiaSmartRoadisa3.2km(2‐mile),test‐adaptablefacilityfor
transportationresearchandevaluation.Thetestroadincludes12flexiblepavement
testsections;atransversallytinedcontinuouslyreinforcedconcretepavement
(CRCP)section,ajointedreinforcedconcretepavement(JRCP)sectionwithsome
groundareas,andtwohigh‐frictionepoxy‐basedsurfacetreatments.Theroadhasa
maximumlongitudinalgradeof6percent.Sincethetwolaneswerepavedat
slightlydifferenttimes,theuphill(westbound)anddownhill(eastbound)laneshave
slightlydifferentsurfacemicro‐andmacrotexture.Bothdirectionsweretestedin
eachrun.Twelvesectionseachapproximately100meters(300feet)longwere
selectedforthefrictioncomparisons,andeachsectionwastestedinboth
lanes/directions,resultinginatotalof24testlocations.Fiverepetitionswere
completedforeachdeviceateachlocation.
Ofthenineasphaltsectionstested,sixareSUPERPAVEmixes,twoareStoneMatrix
Asphalt(SMA)andoneisanOpenGradedFrictionCoarse(OGFC).Theconcrete
sectionsincludedaCRCPwithtinedfinishing,andtwoepoxyoverlaysconsistingof
adoublelayerofaggregatebondedbyepoxycoatings.Figure2showsexampleof
thedifferenttypesofpavementsurfacestested.Withineachpavementsection,
frictiondatawascollectedwiththelocked‐wheelskidtestersandtheGriptester
tiresalignedtothecenteroftheleftwheelpath.Fiverepetitionswereplannedat
targetspeedsof20,40and50mphtoanalyzetheeffectsofspeedonskid
resistance.Frictionatspeedsof20,40,60and80km/hwererecordedfortheDFT
(asperASTME1911,(ASTM1998).
13
a) Lockedwheelsmooth/ribbed
(LWS1)and(LWR1)
b) Griptester
(GT)
c) Lockedwheelsmooth
(LWS2)
d) Skidwheeltesters
(LWS2)
e) CircularTrackMeter
(CTM1)
f) DynamicFrictionTester
(DFT)
FIGURE1.Frictionandmacrotexturetestingequipment
14
SM9.5DSUPERPAVE
OGFC
SMA9.5D
TinedCRCP
StandardVDOTepoxyoverlay(EP)
Proprietaryepoxyoverlay(Cg)
FIGURE2.SampleofpavementsurfacesavailableattheVirginiaSmartRoad.
5.RESULTSANDANALYSIS
5.1ChangesofFrictionwithSpeed
Inordertostandardizetheresultsofthefrictionmeasurementsatvariousspeeds,
anexponentialregressioncurvewasfittedtothesetofpointsonthefrictionversus
speedrelationshipforeachsectionandforeachdevice.Theequationswereusedto
obtainnormalizedvaluesoffrictionforthespecificslipspeedsasrecommendedby
Wamboldetal.(Wamboldetal.1995).Theexponentialregressionfitwasselected
basedontherecommendationsofthePennStateModel,onwhichthePIARCmodel
wasestablished,tocalculatetheskidnumberatthespecifiedSslipspeed(Henry
2000):
15
(4)
where,
μ=calculatedcoefficientoffrictionatthespecifiedslipspeedforeachdevice
μ0=projectedcoefficientoffrictioninterceptatzerospeed
PNG=percentnormalizedgradient(thespeedgradienttimes100dividedby
thefriction,asdefinedby:
€
PNG = −100
µdµds
S=slidingvelocity
5.2IFIComparisons
ToevaluatewhetherornotthecoefficientsdevelopedduringthePIARCexperiment
applytothedevices,theIFIvalueswerecomputedusingthedifferentfrictionvalues
(FR)measuredbythevariousdevicesusedintheequipmentcomparison.
Table1showstheIFIvaluescalculatedforthevariousdevicesandforevery
pavementsectionontheuphillanddownhilllanes.Theprocedurefollowedto
obtaintheIFIwastheonespecifiedinPIARC(1):computeF(60)valuesusing
equations(1),(2),and(3)andincorporatingtherespectivefrictionvaluesatthe
recommendedslip[FR(S)]fromequation(4).ThestandardIFIequationforthe
DFTesterandCTMeterinASTM1960‐07(HenryandSiato1983)wereused.The
specifiedslipspeedswere65km/hfortheskidtesters,20km/hfortheDFT.Witha
15.6percentslipratioas(intheGriptestermanufacturerspecifications,the
Griptesternumbers(GN)weretakenat9.4km/htomatchthePIARCconditions;
otherwisethecoefficientstoestimateF(60)wouldnotapply.
ThemacrotexturemeasurementsobtainedfromtheCTMeterwereusedto
determineSpusingequation(1)anda=14.2andb=89.7(Wamboldetal.2006).
16
ThefrictionnumberF60wasfinallycomputedusingequation(3),withthe
coefficientscorrespondingtoeachdeviceintheoriginalPIARCreport(Wamboldet
al.2006).Themarkerslabeledare“original”inFigure3comparetheresultsfor
eachofthefourdevicesusedwiththestandardDFTvalues,asrecommendedin
ASTM1960‐07.ThecomputedIFIvaluesforthesamepavementsectionsobtained
usingdifferentdevicesareclearlynotinagreement.UsingtheoriginalPIARC
coefficients,theregressioncorrelationcoefficientsforthemeasurementswith
smoothtiresshowrelativelyweakcoefficientsofdetermination(R2).Thissuggests
thatthecoefficientsA,B,andCmayneedtobeadjustedforeachdeviceconsidered
beforetheIFIcanbeimplementedbytheparticipatingagencies.
TheA,B,andCcoefficientswerethenrecalculatedbyplottingtheF60DFTvalues
againstalltheFR60valuesforallthefrictioninstrumentsandfittingalinearmodel
usingregressionanalysis(asrecommendedbyASTM1960‐07).Twoparameters,A
andB,weredeterminedforthemeasurementswiththesmoothtires.Fortheribbed
tireresults(LWR1),amultipleregressionwasperformedincludingallthreeA,B,
andCcoefficients,whichproducedahigheradjustedR2.Thepredictedvaluesusing
theserevisedcoefficientsarealsodisplayedinFigure3(redtriangles).
17
TABLE1.SummaryofIFI’sfrictioncomponentvaluesfordifferentequipmentCTM DFT F60WithOriginalCoefficients F60WithRevisedCoefficients
SectionMPD F60 LWS1 LWS2 GT LWR1 LWS1 LWS2 GT LWR1
1 Loop 1.003 0.482 0.596 0.531 0.534 0.485 0.480 0.472 0.479 0.460
2 A 0.530 0.412 0.519 0.497 0.392 0.476 0.448 0.461 0.425 0.444
3 B 0.680 0.457 0.538 0.468 0.454 0.474 0.456 0.451 0.448 0.447
4 C 0.710 0.445 0.545 0.431 0.439 0.459 0.459 0.440 0.443 0.440
5 D 0.557 0.394 0.438 0.355 0.419 0.428 0.414 0.415 0.435 0.421
6 I 0.923 0.481 0.552 0.544 0.489 0.489 0.462 0.476 0.462 0.460
7 J 1.047 0.460 0.572 0.499 0.492 0.491 0.470 0.462 0.463 0.464
8 K 1.627 0.452 0.501 0.488 0.551 0.448 0.440 0.458 0.485 0.458
9 L 1.003 0.449 0.506 0.448 0.547 0.435 0.442 0.445 0.484 0.436
10 Cg 1.837 0.516 0.597 0.492 0.522 0.562 0.481 0.459 0.474 0.518
11 EP 1.197 0.432 0.520 0.436 0.428 0.467 0.448 0.441 0.439 0.456
12 CRCP 0.703 0.439 0.434 0.357 0.414 0.479 0.412 0.416 0.433 0.450
13 CRCP 0.803 0.465 0.568 0.486 0.455 0.495 0.469 0.457 0.449 0.460
14 Cg 1.860 0.538 0.607 0.552 0.537 0.609 0.485 0.478 0.480 0.541
15 EP 1.173 0.458 0.602 0.545 0.434 0.486 0.483 0.476 0.441 0.465
16 L 1.083 0.450 0.524 0.487 0.529 0.451 0.450 0.458 0.477 0.446
17 K 1.803 0.457 0.495 0.483 0.539 0.452 0.438 0.456 0.481 0.464
18 J 0.847 0.442 0.550 0.520 0.426 0.468 0.461 0.468 0.438 0.448
19 I 0.727 0.436 0.572 0.492 0.417 0.468 0.470 0.459 0.435 0.445
20 D 0.697 0.436 0.493 0.435 0.448 0.443 0.437 0.441 0.446 0.432
21 C 0.787 0.441 0.544 0.484 0.441 0.462 0.459 0.457 0.444 0.444
22 B 1.007 0.477 0.580 0.567 0.515 0.492 0.473 0.483 0.472 0.464
23 A 0.887 0.468 0.574 0.546 0.489 0.460 0.471 0.477 0.462 0.445
24 Loop 0.797 0.447 0.471 0.405 0.434 0.431 0.428 0.431 0.441 0.429
18
a)Locked‐wheelTrailer1w/smoothtire b)Locked‐wheelTrailer2w/smoothtire
c)Griptester(smoothtire)
d)Locked‐wheelTrailer1w/ribbedtire
FIGURE3.IFIF60valuesfordifferentequipmentversusDFTF60values
Furthermore,thecoefficientsofdetermination(R2)forthesmoothtiresindicate
relativelyweakrelationships(lefthalfofTable2),withtheGriptesterhavinga
relativelybettercorrelation.Someofthedifferencesmaybeexplainedbecauseof
theuseofthedefaulttexture‐Sprelationship(equation(6))asdiscussedintheNext
section.Table2comparesthePIARCcoefficientswiththerevisedcoefficients
computedforeachofthedevices.
19
TABLE2.SummaryofF60IFIcoefficientsfordifferentfrictionunits
OriginalCoefficients RevisedCoefficientsFrictionUnit A B C R2 A B C R2
0.2480 0.3898 ‐ 0.48LWS1 0.0446 0.9250 ‐ 0.35
0.2595 0.2957 0.0382 0.700.3152 0.2976 ‐ 0.38
LWS2 0.0446 0.9250 ‐ 0.370.3194 0.2042 0.0395 0.610.3072 0.3460 ‐ 0.41
GT 0.0821 0.9104 ‐ 0.620.3385 0.2018 0.0308 0.50
LWR1 ‐0.0228 0.6068 0.0976 0.78 0.1905 0.2925 0.0718 0.75
Althoughthebiasiscorrectedwiththerevisedcoefficients,therearestillsome
sectionsforwhichtheequationsforthesmoothtiredonotwork.Somepointswith
lowandhighDFTF60arequitefarfromtheequalityline.Sincethesesectionshad
thelowestandhighestmacrotexturevalues,newlinearregressionswithtwo
variables(FR(60)andTX)weredetermined.Thebest‐fitcoefficientsareshownin
blueintherighthalfofTable2andthepredictedvaluesarepresentedgraphically
(asgreensolidcircles)inFigure4.Thefittingwassignificantlyimprovedas
indicatedbythehighercoefficientsofdeterminationobtained.
20
FIGURE4.ComparisonoforiginalandrevisedF60valuesusingthree
parameter(A,B,C)models.
5.3SpeedParameterCalculation
ToevaluatetheappropriatenessofthecoefficientsusedtocomputetheSpbasedon
theMPDvaluesobtainedwiththeCTMeter,thecomputedSpvalueswerecompared
withtheexperimentalvaluesobtainedfromthemodelfittingwithequation4
(PennsylvaniaStateUniversitymodel).Theoretically,theSpfactorshouldbeequal
totheinverseofthePNGvalueindecimalform(100/PNG),orasreferredinother
publicationsastheSo(Henry2000).Sincetheexponentialmodelsweredefinedfor
thevariousdevicesandthevariouspavementsections,itwaspossibletodetermine
anexperimentalSpthatcouldbecomparedwiththeSpvaluecomputedasa
functionoftexture.Itisimportanttonotethattheresultingrelationshipsarevalid
21
onlyforthesurfacesevaluated.Table3showstheresultsofcomparingthe
experimentalvaluesofSpandthecomputedvalueinaccordancewiththeASTM
coefficientcalculationprocedure.Figure5comparestheexperimentaland
computedSpvaluesandshowsthebest‐fitlineal(Sp=a+b∗TX)andpower(Sp=
a∗TXb)models.
TABLE3.ExperimentalandCalculatedSpValuesCTM ASTM ExperimentalSp(km/h)
SectionMPD Sp(MPD) LWS1 LWS2 GT LWR1 DFT
1 Loop 1.00 104 68 75 40 109 2932 A 0.53 62 51 50 16 127 2913 B 0.68 75 44 49 20 154 3014 C 0.71 78 40 63 21 159 3165 D 0.56 64 32 38 24 167 3286 I 0.92 97 68 56 27 141 3377 J 1.05 108 53 83 125 132 3388 K 1.63 160 76 86 28 87 3269 L 1.00 104 53 67 31 99 30710 Cg 1.84 179 48 127 45 169 59911 EP 1.20 122 55 88 53 200 12 PCC 0.70 77 30 34 15 156 54613 PCC 0.80 86 51 69 29 156 51514 Cg 1.86 181 54 89 93 159 58815 EP5 1.17 119 104 175 83 164 16 L 1.08 111 69 81 23 99 39217 K 1.80 176 84 83 127 69 40218 J 0.85 90 67 62 70 161 44119 I 0.73 79 47 64 29 139 33120 D 0.70 77 42 45 25 147 33221 C 0.79 85 53 58 28 164 36522 B 1.01 104 75 73 68 175 39523 A 0.89 94 68 81 54 164 33224 Loop 0.80 86 45 46 19 97 282
22
FIGURE5.ComparisonofcomputedandexperimentalSpvalues
23
Thebest‐fitmodelparametersforeachdevicearepresentedinTable4.Theplotsin
Figure5showthatneitherofthemodelsresultsinhighcoefficientsof
determination.AlthoughitwasreportedintheresultsoftheHERMESexperiment
thatSphadbettercorrespondencewhenusingapowermodeloftheformSp=
a∗TXb,theresultsofthemeasurementsshowthattheexperimentaldataanalyzed
onlyconfirmedthisforthedeviceswithsmoothtires,whereasthecoefficientsof
determinationfortheDFTandribbedtiredonotimprovewithapowermodel.
TABLE4.Coefficientsaandb.Lineal Power
Devicesa b R2 a b R2
DFTSp 122 259 0.2611 378 0.300 0.2247
LWR1Sp 18.3 160 0.0492 136 ‐0.211 0.0823
LWS1Sp 20.0 37.1 0.2096 56.4 0.469 0.3156
LWS2Sp 47.1 25.0 0.3848 70.7 0.767 0.5609
GT 48.0 ‐2.95 0.3342 39.4 1.168 0.4312
6.FINDINGSANDRECOMMENDATIONS
Inthispapermeasurementsobtainedwithdifferenttypesoffrictionmeasuring
equipmenton24pavementsectionswithawiderangeoftextureswerecompared.
Therelationshipbetweenfrictionandspeedforthedifferentpavementsectionsand
deviceswasstudied.Themainconclusionsoftheanalysisofthedatacollectedare
presentedfollowing.
ThedatacollectedforthisprojectshowedthatthemodeldevelopedbyPIARCdoes
notproduceharmoniousresultsamongthedevicesusedbytheconsortium
membersintheVirginiaSmartRoadRodeoforthesurfacestested.Discrepanciesin
theIFIvaluescalculatedforthedifferentdevicessuggestthattheoriginal
24
coefficientsdeterminedduringthePIARCexperimentmayneedtobeadjustedfor
thedevicesevaluatedbeforetheIFIcanbeimplementedbytheparticipatingDOTs.
Thereseemstobeaslightlybettercorrelationofthespeedconstantgradientvalue
withthepowermodelasrecommendedbytheHERMESProjectthanwiththelinear
modelasusedintheoriginalPIARCmodel,particularlyforinstrumentsusing
smoothtires.Basedontheresults,newcoefficientshavebeenproposedforthe
equipmentusedintheSmartRoadRodeoforthetypesofsurfacestested.
StartingwiththePIARCexperiment,harmonizationinitiativesaredoneregularly
becauseithasbeenfoundthatunderdifferentconditionsdifferentparametersand
coefficientswillresult.Itisstronglyrecommendedequipmentcomparison
experiments(liketheNASAandSmartRoadprograms)continueinordertobetter
determinethecoefficientsnecessaryforharmonization.
7.ACKNOWLEDGEMENTS
ThedatausedforthispaperwascollectedduringtheSecondAnnualEquipment
ComparisonProjectaspartoftheVirginiaConsortiumforPavementSurface
Properties.Thisexperimenthasbeenmadepossiblethankstothecontributionsof
theVirginiaTransportationResearchCouncil(VTRC),theFederalHighway
Administration(FHWA),andtheConnecticut,Georgia,Mississippi,Pennsylvania,
SouthCarolina,andVirginiaDepartmentsofTransportationandtheVirginiaTech
TransportationInstitute(VTTI).
25
8.REFERENCES
ASTMStandardE1960‐98StandardPracticeforCalculatingInternationalFriction
IndexofaPavementSurface,ASTMInternational,WestConshohocken,PA.
Descornet,G.TheHERMESProject.InSURF2004.(CD‐ROM).5thSymposiumon
PavementSurfaceCharacteristics,WorldRoadAssociation,Paris,2004.
Flintsch,G.W.,deLeon,E.,McGhee,K.K.,andI.L.Al‐Qadi.PavementSurface
MacrotextureMeasurementandApplications.JournaloftheTransportation
ResearchBoard,TRR1860,Washington,D.C.,2003,pp.168‐177.
Henry,J.J.NCHRPSynthesisoftheHighwayPractice291:EvaluationofPavement
FrictionCharacteristics.TransportationResearchBoardoftheNational
Academies,Washington,D.C.,2000.
Henry,J.J.,andK.Siato.SkidResistanceMeasurementswithBlankandRibbed
TesterTiresandTheirRelationshiptoPavementTexture.Journalofthe
TransportationResearchBoard,TRR946,Washington,D.C.,1983,pp.38‐43.
Wambold,J.,Henry,J.,andT.Yager.NASAWallopsTire/RunwayFriction.InSURF
2004.(CD‐ROM).5thSymposiumonPavementSurfaceCharacteristics,
WorldRoadAssociation,Paris,2004.
Wambold,J.C.,C.E.Antle,J.J.Henry,andZ.Rado.PIARCFinalReport.International
PIARCExperimenttoCompareandHarmonizeTextureandSkidResistance
Measurements.PIARC:PermanentInternationalAssociationofRoad
Congresses.Paris,1995.
Wambold,J.C.,T.J.Yager,J.J.Henry,andZ.Rado(April2006).AWhitePaperon
CorrelationoftheGriptesterTrailertotheASTME274SkidTrailer.
26
CHAPTERIII
FIELDPERFORMANCEOFHIGHFRICTIONSURFACES
ABSTRACT
Eventhoughtherelationshipbetweenroadwaysafetyandpavementfrictionhas
longbeenrecognized,thelackofsufficientfrictionatthetire‐pavementinteraction
isstilloneofthemajorcontributingfactorstovehicleaccidents.Duetothe
relationshipbetweenskidresistanceandaccidentsandtheincreaseoffatalitieson
highways(N.T.S.1999),optimumlevelsofskidresistancemustbemaintainedon
pavementsunderextremeweatherconditions.High‐frictionsurfaces(HFS)are
consistentlybeingconsideredbecausetheyprovidethepavementfrictionneeded
withoutnegativelyaffectingotherpavementqualities,likenoiseordurability.
Theobjectivesofthispaperaretostudysomeofthehigh‐frictionsurfacesavailable
intheUnitedStatesmarket;measuretheirperformance(frictionandtexture)on
differentapplications,underdifferentweatherconditions,andonvariouslocations;
andpresentagenciestheresultsobtainedinapractical,easy‐to‐useform.The
resultsofthebenefit‐costanalysisforthestudiedHFSshowthatonallfourstudied
sectionstheHFSalternativeiseconomicallyjustifiedcomparedtothebasecase.
ThecoefficientsdevelopedwereusedtoobtainInternationalFrictionIndex(IFI)
valuesforeachHFSstudied.Itisrecommendedthatmoreexperimentsberunwith
differenttypesofpavementssurfaces,includingHFSandothertypesofsurface
treatments,todemonstratethevalidityofthespeedgradientcoefficientSp
coefficientsrecommendedbyASTMandalsothevalidityofusingtheDynamic
FrictionTesterasthestandarddevicetomeasurefrictionfortheIFIcalculations.
Researchisrecommendedonpredictingminimumsurfacefrictionvaluesindicating
thenecessityofroadwayrehabilitation.Todeveloptheseparameters,itisnecessary
tostudy,monitor,andcorrelatetexture,friction,andaccidentdata.
1.INTRODUCTION
Roadwayaccidentsarealeadingcauseofdeathandinjuryaroundtheworld.Each
year1.2millionpeopledieandmillionsmoreareinjuredordisabledasaresultof
roadcrashes(Hayesetal.2007).Thisnotonlycreatesanenormoussocialcostfor
individuals,families,andcommunitiesbutalsoplacesaheavyburdenonhealth
servicesandeconomies.
Therelationshipbetweenroadwaysafetyandpavementfrictionhaslongbeen
recognized,butoneofthemajorcontributingfactorstovehicleaccidentson
highwaysisstillinsufficientfrictionatthetire‐pavementinteraction.Ithasbeen
reportedthatwetpavementsareinvolvedin25percentofallcrashesandthat
vehiclesleavingtheirlaneorrunningofftheroadareinvolvedin59percentof
roadwayfatalities(NTS1999).
ThevolumeandseverityofmotorvehiclecrashesintheUnitedStateshasledthe
FederalHighwayAdministration(FHWA)todeclaresafetyasoneoftheirtop
priorities.Itisforthisreasonthathigh‐frictionsurfaces(HFS)arebecomingan
appealingpavementhighfrictionapplicationalternativesincetheyhavetheability
toincreasefrictionandimprovetexturebyutilizingahigh‐polished‐stone‐value
(PSV)aggregateandsometypeofresintoholdtheaggregateparticlestogetherand
gluedtotheroadsurface.
Motorvehiclecrashesresultfromnumerouscontributingfactors,includingdriver
error,poorgeometricalignmentoftheroadway,andinsufficientfrictionatthetire‐
pavementinteraction,especiallyduringwetweather.HFSshaveemergedasviable
pavementhigh‐frictionalternativesthatmitigatesomeofthesefactors.
BesidesHFSthereareotheralternativesthathavetheabilitytoincreaseskid
resistanceonpavements,suchastinningorgroovingonrigidpavements.However,
28
mostofthesesurfacealterationsadverselyaffectothersurfaceproperties,suchas
noisegeneratedbetweentireandpavement.HFSareusedforincreasingroad
surfaceskidresistance,driverawareness,andwaterdrainageanddecreasing
brakingdistance,hydroplaning,splash,andspray.
2.OBJECTIVE
AstudyconductedbytheUniversityofMichiganon15rampsat11interchangesin
5statesfoundthatsurfacepropertieswererelatedtotruckalongwithgeometry,
andvehicledynamics(JulianandMoler2008).
Ithasalsobeenshownthereisastatisticallysignificanteffectofskidresistanceon
wetaccidentrate:thewetaccidentrateincreaseswithdecreasingskidresistance
(Kuttesch2004).Duetothisrelationshipandtheincreasingnumberoffatalitieson
highways,optimumpavementskidresistancemustbemaintainedunderextreme
weatherconditions(N.T.S.1999).High‐frictionsurfaces(HFS)arebecomingan
appealingpavementhighfrictionapplicationalternativebecausetheysupplythe
neededpavementfrictionwithoutnegativelyaffectingotherpavementqualities,
suchasnoiseanddurability.
Theobjectivesofthispaperare:
1)ToidentifythemainHFSavailableintheUnitedStatesmarket.
2)Tomeasuretheirperformance(frictionandtexture)ondifferentapplications,
underdifferentweatherconditions,andonvariouslocations,and
3)Topresentagenciestheresultsobtainedinapractical,easy‐to‐useformat.
ThispaperisaimedathelpingagenciesdecidewhetherornotanHFSshouldbe
appliedataparticularlocationandwhichHFSisthemostappropriateforaspecific
application.Theinformationcompiledwillhelpdecisionmakersallocatetheneeded
resourcestoaddressthemostserioussafetyrisks.
29
In2006,theVirginiaTransportationResearchCouncil(VTRC)andtheVirginiaTech
TransportationInstitute(VTTI)initiatedaregionalpooled‐fundprojectknownas
thePavementSurfacePropertiesConsortium.Thisprojectestablishedaresearch
programfocusedonenhancingthelevelofserviceprovidedbytheroadway
transportationsystembyoptimizingpavementsurfacetextureandfriction
characteristics.TheprogramwassetupwithsupportfromtheFHWAandincludes
sixDOTsfromthestatesofConnecticut,Georgia,Mississippi,Pennsylvania,South
Carolina,andVirginia.Thisfive‐yearprogramispartoftheactivitiesoftheVirginia
SustainablePavementResearchConsortium(VA‐SPRC)andismanagedbyVTRC
andrunbytheCenterforSustainableTransportationInfrastructure(CSTI)atVTTI.
3.BACKGROUND
Thetermhighfrictionsurface,orHFS,referstosurfacetreatmentsthatutilizeanon‐
polishableaggregate(withhighpolishedstonevalue,PSV)andsometypeofresin
(binder)toholdtheaggregateparticlestogetherandgluedtotheroadsurface.The
mostcommonlyusedaggregateiscalcinedbauxite.
TheoriginofHFSdatestothemid1950swhentheuseofepoxy‐resinsasbinderson
surfaceswasfirststudied(Nicholls1998).Inthe1960stheU.K.government’s
TransportandRoadResearchLaboratory(TRRL)begantotesthardaggregateswith
variousbinderstoproduceextremelyhigh‐frictionsurfaces.Yearslater,theGreater
LondonCouncil(GLC)concludedthatthemosteffectiveHFSresultedfromthe
combinationofcalcinedbauxiteof0.32cmwithabitumenextendedepoxy‐resin
binder(JulianandMoler2008).Inthelate1980sresearchersintheUnitedStates
begantoinvestigatetheeffectivenessofthesesurfacingsystemsinreducingcrashes
onblackspots.
30
3.1HighFrictionSurfacesApplicationProcesses
Accordingtotheformofapplication,HFScanbeclassifiedintotwocategories:cold‐
appliedandhot‐appliedprocesses(Nicholls1997).Cold‐appliedHFSuse
thermosettingresinslikeepoxyorpolyurethane,whicharesuppliedindifferent
containersandthenmixedtobeginaheat‐producingchemicalreactionthatresults
inhardening.Inthehot‐appliedprocessthepremixedgranularmaterialisprovided
inbags,thenheatedinaboilerandappliedtothesurfacewhilestillhot.Inthiscase
theresinusedisthermoplastic.
3.2HighFrictionSurfaceBinders
ThereareseveraltypesofresinsusedonHFS,andeachaddsuniquecapabilitiesto
thesystem.Themainresinsare:epoxy‐resin,rosin‐ester,polyurethane‐resin,and
acrylic‐resin(Nicholls1998).
3.2.1EpoxyResin
TheoldestresinusedonHFSistheepoxy‐resin.Itconsistsofatwo‐component
systemmixedonsiteatequalquantitiesbyweight.Onecomponentcontainsthe
resintogetherwithaproportionofoilthatreducestheviscosityoftheresinand
actsasanextender,whiletheothercontainsthecuringagenttogetherwith
bitumen,anoilextender,andaccelerators.Thepropertiesofthebindercanbe
adjustedbychangingtheproportionsofthecomponentsofthesystem;
nevertheless,atypicalcuringtimeoscillatesbetweenthreetofourhoursfor
temperaturesabove10°C.
3.2.2RosinEster
Apre‐blendedsystemliketherosin‐esterfacilitatesinsituinstallationoperations
sincetheresinandaggregatesarealreadymixedandbaggedtogether,readytobe
heatedatthespecifiedtemperatureandplacedonthesurface.
31
ThistypeofHFSisappliedwithahandheldbox,resultingina5‐mmthicknessthat
stiffensquicklybecauseofitsthermoplasticnature,allowingDOTstoreopenthe
roadwithminimumdelay.
3.2.3PolyurethaneResin
Thepolyurethane‐resinwasmainlydevelopedtoachievequickercuringtimesat
lowtemperaturesthanotherexistingsystems.Itisachemicallycuringmultiple‐
componentsystem.Thecomponentsaremixedtogetherwithahandheldbeaterand
laidbyhand.Afterward,theaggregateisspreadseparatelyandalsobyhand.
3.2.4AcrylicResin
Thisisatwo‐componentsystemwithmuchfastercuringtimethanepoxy‐resin.
Consequently,thecuringprocessdoesnotbeginuntiltheaggregate,whichcontains
thecuringagent,isspreadoverthesurface.Theconsistencyofthisbinderis
designedtowettheaggregatesufficiently,inordertoprovideanadequatebond
withoutthebindersubmergingthechips.
3.3PropertiesofAggregatesforHighFrictionSurfaces
AggregatesonHFSshouldprovideaskid‐resistantsurfacewhilebeingnon‐
polishable,durableagainsttheabrasioneffectsoftraffic,andresistanttothe
disintegrationprovokedbyweathering. Thesurfacelayerneedstoretainitstexture
foraslongaspossibletoprovideskidresistancefortraffic.ThehigherthePSV,the
longertheaggregatewillremainroughwhenusedinroadsurfacing.
3.3.1StandardPracticefortheAcceleratedPolishingofAggregatesUsingthe
BritishWheel(AASHTOT279,ASTMD3319)
Thismethodsimulatesthepolishingactionofvehiculartrafficonaggregatesusedin
pavements.Polishvalue,isameasureofthestateofpolishreachedbytest
specimenssubjectedtoaspecifiednumberofhoursofacceleratedpolishingusing
32
theBritishwheel,thisvaluemaybeusedtorateorclassifyaggregatesfortheir
abilitytoresistpolishingundertraffic.
Thefirststepinthisprocedureistodeterminetheinitialfrictionvalueofeach
preparedtestspecimenbyusingtheBritishPendulum,thenthespecimensare
clamparoundtheperipheryoftheroadwheelusingrubbero‐ringsneartheedgeof
thespecimensinordertoformacontinuousstripofparticlesuponwhichthetired
wheelshallridefreelywithoutbumpingorslipping.
Duringthetest,specimensaresubjectedtoa320rpmroadwheelwithatotal
surfaceloadof391N(88lbf),anda66g/minrateofsiliconcarbide.Afterthe
polishingactionhaspassedthespecimensareremovedfromthefixture,wash
thoroughlytoremovegritanditsfrictionvalueobtainedthrutheBritishpendulum,
inordertodeterminethepolishvalue(ASTM2006).
Duringtestingaggregatesshouldbesubjectedtoapolishingactionof10h,unless
maximumpolishisachievedinashortertime.Maximumpolishisachievedwhenno
changeisdetectedonsuccessivemeasurements.
3.3.2ResistancetoDegradationandAbrasion(AASHTOT96,ASTMC131)
Thismethodsimulatesdegradationbyabrasionofsmall‐sizedaggregates.Thefirst
stepinthisprocedureistoweighthesample.Thenthesampleandthechargeare
placedintheLosAngelestestingmachineat30rpmfor500revolutions.Afterward,
thematerialisdischargedandasieveanalysisisdone.Lastly,theaggregatesare
washedandweighedtodeterminetheabrasion(AASHTO1991).
3.3.3SoundnessofAggregatesbyFreezeThawing(AASHTOT10391,ASTMC88)
Thistestmethodsimulatesthebehavioroftheaggregateunderfreeze‐thaw
conditionstodeterminedisintegration.Inthisprocedurethetestspecimenshould
bewashed,ovendried,sieved,andweighed.Thenthesamplesareimmersedin
33
waterfor24hourspriorthestartofthefreezingcycleandmustbefrozenand
thawedinthiscompletelyimmersedcondition.Incaseofpartialimmersion,other
proceduresdescribedbyAASHTOmustbefollowed.
Inmanyinstancesafreezingperiodoftwohoursissuitable,dependingonfreezing
equipment.Followingfreezing,thesamplesmustbethawedfor30minutesat70°F
inanalcohol‐watersolution.Thisproceduremustberepeatedfor50cycles.After
thecompletionofthefinalcycle,thespecimensmustbedriedandsievedto
determinedthelossineachsieve(AASHTO1991).
3.4HighFrictionSurfacesAggregates
Theselectionofaggregateswilldependontheirperformanceduringthetests
describedintheprevioussection.Table1presentsthetypesofaggregatesusedin
thestudiedapplications.Themostcommonlyusedsourcesaredescribedbelow.
TABLE1.TypeofAggregateandPriceforSelectedHFSProduct TypeofAggregate AggregateSize
CrafcoHFS Bauxite(China‐Guyana)Granite
1‐3mm1‐3mm
Flexogrid Basalt+graniteSilica
2‐3mm2‐3mm
Italgrip Steelslag(patented) 3‐4mm
Safelane(Cargill) Dolomite 1‐3mm
Safe‐T‐Grip Granite 1.5‐3.2mm
Tyregrip Calcinedbauxite(buffandgrey) 1‐3mm
3.4.1CalcinedBauxite
CalcinedbauxiteaggregatecomesfromanaluminumorecommonlyminedinChina
thatisexposedtoprolongedheatingattemperaturesof1,600°Ctoincreaseits
hardnessandphysicalstability.
34
Thedensityofcalcinedbauxitevariesfrom2.6to3.4g/m3dependingonitssource.
ThispropertyistypicallyagoodindicatorofthePSV:highdensityindicateshigh
PSV.Guyananbauxite(darkgrey)hasaPSVof72whileChinesebauxite
(buff/creamycolor)exhibitsvaluesof67PSV.
3.4.2Dolomite
Somerecentlydevelopedanti‐icingsurfacesuseaggregatesmadeinlargepartofthe
mineraldolomite,whichisthedoublecarbonateofcalciumandmagnesium.
Replacementofpartofthecalciumfromlimestonebymagnesiumisthemost
importantprocessintheformationofdolomite.Thisreplacementisseldom
complete,andmanygradationsexistbetweenlimestoneanddolomite(Huhtaetal.
2001).Dolomiteiscommonlylightincolorandoftenhasferrousironcompounds
thatmayoxidize,tintingtherockshadesofbuffandbrown.
3.4.3Granite
Granitesarecomposedofquartzandpotassiumfeldspar,anditscolorvariesfrom
verylighttomediumtonesofgray.Duetoitsmineralcompositionandinterlocking
crystals,graniteishardandabrasionresistant.Thetoughnessofgraniteisusually
superiortothatofsandstone,limestone,andmarble(Huhtaetal.2001).Itprovides
aPSVof62orgreater.
3.4.4Silica
Silicaoccurscommonlyinnatureassandstone,silicasand,orquartzite.Itistheraw
materialusedfortheproductionofsilicateglassesandceramics.Silicaisoneofthe
mostabundantoxidesintheearth'scrust.Itcanexistinanamorphousform
(vitreoussilica)orinavarietyofcrystallineforms(Huhtaetal.2001).
Therearethreecrystallineformsofsilica:quartz,tridymite,cristobaliteandtwo
variationsofeach(highandlow.)Silicahasgoodabrasionresistanceandhigh
35
thermalstability.Itisinsolubleinallacidswiththeexceptionofhydrogenfluoride
(HF).
3.4.5SteelSlag
Slagisaby‐productofsteelmaking,producedduringtheseparationofthemolten
steelfromimpuritiesinsteel‐makingfurnaces.Theslagformsasamoltenliquid
meltandisacomplexsolutionofsilicatesandoxidesthatsolidifiesuponcooling.
SteelslagmustbecrushedandscreenedtoproduceasuitableaggregateforHFS
(Shi2004).
OtheraggregatesmaybeselectedforuseonHFSfortheirnaturalcolors,whichcan,
bycolorpigmenting,accentuatetheaggregateforgreatervisualimpact.
3.5PreviousHighFrictionSurfacesStudies
TherehavebeenseveraleffortsbydifferentagenciestoevaluateifHFSaresuitable,
durable,andcost‐effectivetechniquestoenhancethesafetyanddrainage
characteristicsofroadways.Themostrelevantarebrieflydescribedinthissection.
3.5.1InvestigativeStudyoftheItalgripSystem–NoiseAnalysis
TheWisconsinDepartmentofTransportationconductedastudytoidentifyand
quantifytheimpactonexteriorvehiclenoiseofapplyingItalgriponaPortland
CementConcrete(PCC)pavement.Thesurfacetreatmentwasinstalledonajointed,
undoweled,transversely‐tinedPCCpavementinWaukeshaCounty.A3‐mm
aggregatewasappliedtobotheastboundlanes,while4‐mmaggregateswere
appliedtowestboundlanes(Kuemmeletal.2000).
ThisstudyconcludedthatItalgripproducesa2‐3decibeldecreaseinnoiselevel
whencomparedtootherpavementsatspeedsof60mphand65mph,anoticeable
changeinsoundtotheear.Itwasalsofoundthatthenoiseleveldifferencebetween
3‐mmand4‐mmaggregatesisinsignificant.
36
3.5.2TrialsofHighFrictionSurfacesforHighways
TheTransportationResearchLaboratoryintheUnitedKingdomconductedaproject
tobetterunderstandthemainfeaturesandperformanceofthedifferentbinder
systemsavailableforHFSapplication.Thebindersystemsstudiedwereepoxy‐resin,
rosin‐ester,polyurethane‐resin,andacrylicresin.
Thisreportdescribesaseriesoftrialsconductedatdifferenttimesusingdifferent
typesofHFS.Thesystemswererankedintermsofmaintainedskidresistance,
texturedepthandlongevity.Thestudyshowedthattheepoxy‐resinand
polyurethane‐resinsystemsmaintainedtheirpropertiesmostconsistently,followed
bytheacrylic‐resinsystemandthentherosin‐estersystem.Itwasalsofoundthat
polyurethaneandacrylic‐resinsystemshaveshortercuringtimesthantheepoxy‐
resinsystems,althoughnotasshortastherosin‐ester,whichallowstheroadtobe
openedtotrafficfaster(Nicholls1998).
3.5.3EvaluationofCargillSafelaneEpoxyOverlay
(Sprinkeletal.2008))evaluatedtheperformanceoftheSafelanesystemwhen
comparedtoaconventionalmodified‐epoxyconcreteoverlay.TwoSafelaneandtwo
EP5systemswereplacedonaninterstate’sbridgedecksandontheVirginiaSmart
Road.
ThestudyshowedthatSafelaneoverlaycouldprovideaskid‐resistantwearingand
protectivesurfaceforbridgedecks.Theprojectwasnotabletodeterminethe
performanceoftheoverlaywithrespecttoprovidingasurfacewithless
accumulationoficeorsnowwhencomparedtotheconventionalepoxyoverlay.
37
3.5.4PerformanceofPolyCarb,Inc.FlexogridBridgeOverlaySystem
(AdamandGansen2001)evaluatedtheperformanceoftheFlexoGridsystemona
highwaybridgedeckinthestateofIowaoverafive‐yearperiod.Resultsshowed
thatthisHFSsystemincreasedfrictionmeasuredwithalocked‐wheeltrailerfrom
36.5SNto67.5SN,andfouryearsafterapplicationarecordedfrictionof64.5
resulted.Itwasalsofoundthatonthesixthyear,530ft2ofthe14,080‐ft2bridgewas
alreadydelaminated.Thisresearchattributesthedelaminatingproblemtomoisture
trappedbelowtheimpermeablePolycarblayer.
3.5.5FloridaDOTTyregripForensicReport
In2008theFloridaDOT(FDOT)studiedoneoftheirItalgripHFSapplicationsto
investigatemixedreviewsfromthoseinvolvedwiththeapplicationconcerningthe
causesofravelingonthesystem.Theresearchdiscoveredthatthemaincausesof
ravelingonthisapplicationwereimproperepoxypreparation,humidityofsurface
priortoapplication,andthinningofepoxyapplication.Thisstudyshowsthe
importanceofmechanicalapplicationinachievinguniformityalongthesurfaceand
avoidingraveling(Kelly2008).
3.5.6EvaluationofInnovativeSafetyTreatments
(Reddyetal.2008)evaluatedinnovativesafetytreatmentsimplementedby(FDOT)
andotheragenciestodeterminetheirimpactoncrashesandothersurrogate
measures.Thesetreatmentsincludedtemporaryrumblestrips,whiteenforcement
lights,motoristawarenesssystem,countdownpedestriansignals,in‐roadwaylights
andTyregriphigh‐frictionsurface.ThisevaluationconcludedthattheHFS
(Tyregrip)areeffectiveinincreasingfrictionbetweentheroadwayandvehicletires.
Thesystemiseffectiveinassistingdriversinmaintainingtheirlanepositionunder
wetpavementconditions.Thisresearchalsoinfersthatdriverstendtoslowdown
whentravelingovertheHFSsection.
38
3.5.7InvestigativeStudyofItalgripSystem2008
(Bischoff2008)studiedfivedifferentItalgripapplicationstoassessifthissystemis
asuitable,durable,andcost‐effectivetechniquetoenhancethesafetyanddrainage
characteristicsofroadways.Locked‐wheelfrictiontestingshowedthatthesystem
increasedthefrictionnumberfromanaverageof42.9SNto72.6SNafter
application.Afterfiveyearsinservicethesiteshadanaverageof59.4SN.This
showedthateventhoughfrictiondecreased,theaveragefrictionnumberwasstill
38percenthigherthanbeforetheapplication.Theresultsalsoshowedthatnumber
ofaccidentsatsitesdecreasedby93percent,thenumberofvehiclesinvolvedin
accidentsdecreasedby89percent,andthenumberofaccident‐relatedinjuriesby
86percentduringathree‐yearperiod.Itwasalsofoundthat4‐mmaggregates
showedbetterfrictionthan3‐mmaggregatesandthatthisHFSsystemcouldreduce
thetire‐pavementnoiseby4decibels.
3.6HighFrictionSurfaceSystemsStudied
TheHFSinvestigatedforthisthesiswereselectedbysearchingontheworldwide
webforHFSavailableallovertheworldandthencontactingthosecompaniesto
findaU.S.supplier.Inaddition,theFederalHighwayAdministration(FHWA)
providedalistofdepartmentsoftransportationthathadtriedsomeofthehigh‐
frictionproducts,andtheywerecontacted.Theproductsevaluatedarediscussed
below.
3.6.1CrafcoHFS
TheHFSofferedbyCrafcoisachemically‐engineeredmodified‐epoxyoverlay
designedtoprovideaflexiblehigh‐frictioncoatingforbridges,highways,andother
roadways.Thisepoxy‐polymeroverlayconsistsofatwo‐componentepoxybinder
thatisappliedtothesurface,whichisthencoveredbyselectedaggregates.Because
oftheirproperties,theseselectedaggregatesensurethatuponfracturetheywill
micro‐fracture,remainingsharpandretaininghighskidresistance(Crafco,2008).
39
TheCrafcosystemoffersvariousaggregateschoices,whichprovidedistinct
frictionalcharacteristics,colors,anduses.BauxitechippingsfromChinaandGuyana
areavailableinnaturalcolorsandareusedwherehighsurfacefrictionandlong‐
termwearresistancearerequired.Americangraniteaggregate(suppliedinnatural
silverandred)isusedwhengoodsurfacefrictioniswanted.Othercolored‐coated
aggregatesmaybeusedtoimprovedriverawareness.
CrafcoHFSiscomposedofathermosetting,primerless,low‐odorepoxycompound,
whichexhibitsplastoelasticpropertiesbondingtheaggregatepermanentlyin
position.Thisflexiblesurfaceisdesignedtoberesistanttofuel,de‐icers,oil,and
impacts.
3.6.2Safelane(Cargill)
TheSafelanesystemconsistsofacombinationofepoxyandproprietarydomestic
dolomiteaggregateusedtoimprovefriction.Thissurfacecanbechargedwith
standardanti‐icingfluidsthatstorethechemicalsandreleasethemautomatically
undersnowconditions,preventingicefromformingonroadwaysandbridgedecks
(Cargill,2008).
3.6.3Tyregrip(PrismoEnnisPaint)
TheTyregripsystemisatwo‐partcold‐appliedexothermictreatmentformedbyan
epoxy/aminebinderandnaturalorpigmentedaggregates,whichusuallyarebuffor
graycalcinedbauxite.Theaggregateusedinthissystemisgradedfrom1mmto
3mm.Theleveloffrictionforthesystemcanbevaried.Forexample,calcined
bauxitecanbeusedtorenderaPSVof68orgreater.ThisHFSisavailableina
varietyofcolors.Tyregripofferscolor‐coatedchippingsaswellaspigmentedand
unpigmentedbinders(Tyregrip,2008).
40
3.6.4Italgrip
ItalgripwasimplementedforthefirsttimeintheUnitedStatesin1999.ThisHFS
systemconsistsofatwo‐partpolymer‐resinplacedoneitherasphaltconcrete(AC)
orPCCpavementsurfaceandcoveredwithanartificialaggregateofre‐workedsteel
slag3to4mminsize.TheItalgripsystemprovideshighfrictionandhasalsobeen
foundtoreducehighwaynoise.Thisthinsurfacetreatmentisprimarilyintendedfor
applicationinheavilytraffickedareasexperiencingfrictionproblemsorhigh
accidentratesovershortsectionsofroadway(Italgrip,2008).
3.6.5FlexoGrid(Polycarb)
TheFlexoGridsystembinderisachemicalcombinationformedbyanepoxyand
urethanedesignedtoprovideaflexible,waterproofingmembranewithsufficient
strengthtowithstandsnowplows,coldandhotweather,andthepoundingfrom
carsandtrucks(Polycarb,2008).Thisproductutilizesflintaggregate(silica)ora
combinationofbasalt‐granitechipstoprovidethedesiredsurfacefriction.The
materialsusedforthisapplicationaredomestic,includingthebinder.This
applicationisdesignedtobeinstalledonconventionalconcrete,concrete‐filledsteel
griddecks,steelplatedecks,fiberreinforcedpolymerdecks,andasphalt.
3.7HighFrictionSurfacesTypicalApplicationProcedure
ThetypicallyrecommendedlocationsforHFSinstallationsincludeareasofhigh‐
frictiondemandlikebridges,intersections,roundabouts,tollplazas,buslanes,exit‐
entranceramps,approachestocrosswalks,schoolcrossings,corners,steepgrades,
horizontalcurves,andotheridentifiedhazardousareas.ThemainbenefitofHFS
systemsisthattheysavelives;applicationinthecorrectlocationshasbeenproven
toresultinaccidentreductions(JulianandMoler2008).Otherreportedbenefitsof
HFSarefastapplication,retro‐reflectionnighttimehazard‐warningcapabilities,and
simplehandormachineapplication.
41
ThegeneralprocedureforinstallinganHFSstartsbypreparingtheroadsurface.It
mustbeclean,dry,andfreefromice,frost,looseaggregate,oil,grease,roadsalt,and
otherloosematterlikelytoimpairadhesionofthesystemtotheroadsurface.This
isaccomplishedusingbrooms,compressedair,andshotblastingonconcrete
surfaces.Then,thesurfacetemperatureshouldbemeasuredtoensureitisabove
theresininstallationstandard.Subsequentlydrainsandexpansiondevicesmustbe
coveredwithducttapeandplastictopreventcloggingwithepoxyandaggregates.
Thetwocomponentsoftheepoxyareusuallydeliveredin55‐gallonsdrumsthatare
laiddownatthesiteandgravityfedintobucketsofpredeterminedvolumeinapre‐
establishedproportion.Thiscombinationismixedwithaslow‐speeddrillfitted
withahelicalmixingblade.However,thisstepisnotnecessarywhenmetered
sprayingisusedtoplacetheepoxy.
Beforetheresinisspreadmanually,gridsshouldbelaidoutwithtapetocontrolthe
applicationrateoftheepoxy.Immediatelyaftertheepoxyisspread,workersuse
shovelsandbroomstoevenlyspreadtheaggregatesoverthebinderaspresentedin
Figure1.Finallytheexcessaggregateisremovedandthesystemislefttocurefora
periodoftwotofourhours.
Inatypicalapplication,theepoxyisspreadatanapproximaterateof2.6to3square
yards(27sq.ft)pergallon,andtheaggregateisspreadatarateof14‐15square
yardsper200poundsofaggregate.Thisissimilartotheapplicationrateofone
epoxygallonforeach25sq.ftcoveredforSafelaneapplicationattheVirginiaTech
SmartRoad.
42
a)MixingA‐BEpoxycomponents
b)Binderisspreadbycrew
c)Aggregateisspreadbycrew
FIGURE1.Highfrictionsurfaceapplication(AdamandGansen2001).
3.8HighFrictionSurfacePotentialSourcesofFailures
AnHFScanfailbecauseofravelingofthematerial,delaminating,orpolishingofthe
aggregate.Thefailurecanbeattributedtoconstructionmethods,product
performance,and/orenvironmentalconditionsduringapplicationandinservice.
Themostimportantconcernsarediscussedbelow.
3.8.1EpoxyPreparationComposition
Thetwo‐partmodifiedepoxyusedonmostoftheHFSapplicationsistobemixedin
aspecificratio,andsometimesduetoconstructionerrorsthismaynotbethecase.
43
Thiscouldaffecttheepoxyperformance.Thecompositionofthebindermayalso
affecttheadhesionwiththeaggregateparticlesand/orthepavementsurface.
Somestudiessuggestthatduetothedecreasinguseofcreosolbecauseofitsstrong
odorandabilitytoburntheskinduringapplication,newepoxyformulationsexhibit
worseperformancethanpreviouslyusedcombinations(Kelly2008).
3.8.2EpoxyAggregatePlacement
Epoxyshouldbespreadhomogeneouslyoverthesurfaceandatthecorrectrateto
preventthebinderfromcoveringtheaggregate.Thereneedstobeacomplete
coverageofthewetbinderwithaggregatetoachieveauniformfrictionsurface,and
nowetspotsshouldbevisibleoncetheaggregateisplaced.Thiscouldbedifficultto
accomplishatthemomentofinstallationsincemostofthesesurfacesareappliedat
nightforconvenienttrafficcontrolandtoreduceimpactontrafficflow.
3.8.3ExistingPavementExistingAsphaltCompatibility
SometypesofpavementsareparticularlydifficultfortheinstallationofanHFS.For
example,thehighpermeabilityofporousasphaltsposesathreatinaccomplishinga
uniformepoxysurface(Kelly2008).ItisalsonotrecommendedthatanHFSbe
placedonpavementslessthanonemonthold.Also,sufficientcleaningisnecessary
forallpavements.
3.8.4HumidityandMoisture(SurfaceandAggregate)
HumidityandmoistureareofgreatconcernatthemomentofHFSapplication.
Surfacehumiditycausedbycondensationandfogimpedesthefulladhesionand
performanceoftheepoxyoverthesurface.Likewise,highmoisturecontentinthe
aggregatebeforethesystemisinstalledcouldcompromisetheaggregate’sabilityto
bondwiththeepoxy.Thismoisturecouldcauseravelingandpeel‐offwhentheHFS
isinservice.Forexample,severeravelingmaydevelopasthesurfaceundergoes
freeze‐thawactionduetomoisturetrappedbelowtheimpermeablelayerasshown
inFigure2.
44
FIGURE2.HighFrictionSurfaceRaveling(AdamandGansen2001)
3.8.5AmbientTemperature
Althoughthespecificapplicationtemperaturevariesfromproducttoproduct,the
rangeoftemperatureoverwhichanHFSinstallationisrecommendedisbetween
55°Fand100°F.Toapplythebinderbelowthesetemperatures,thesurfaceshould
beheatedandthesystem’scuringtimeiselongated.
3.8.6CuringTime
Acuringtimeoftwotothreehoursisrequiredformostapplicationsunder
convenientambienttemperatures.Curingwilltakelongeratlowtemperatures,and
optimumperformanceoftheHFSmaybecompromised.
3.9HighFrictionSurfacesFieldEvaluations
SeveralexistinginstallationshavebeenidentifiedintheUnitedStateswithproducts
fromCrafco,Safelane,Tyregrip,Italgrip,andSafe‐T‐Grip.Thecontactinformation
foreachsupplierispresentedinTable2.Themainexperimentalcomponentofthis
thesisstudiesandanalyzestheperformanceoftheseapplications.
45
TABLE2.HFSProductsInstalledintheUnitedStatesProducts Evaluated
Websites Contacts
CrafcoHFS(CrafcoINC)
http://www.crafco.com/ NickNedasOffice:(512)432‐5170Mobile:(602)228‐1269E‐mail:[email protected]
Italgrip(ItalgripUSA)
http://www.italgrip.com/ RobertB.SchmiedlinOffice:(608)592‐2725Mobile:(608)698‐1712E‐mail:[email protected]
Flexogrid(Polycarb)
http://www.poly‐carb.com/ PunitZenMobile:(678)296‐9910Office:(440)248‐1223E‐mail:info@poly‐carb.com
Safelane(Cargill)
http://www.cargillsafelane.com AnthonyHenseyOffice:(866)900‐7258Mobile:(423)488‐6884E‐mail:[email protected]
Safe‐T‐Grip(TrafficCalmingUSA)
http://www.trafficcalmingusa.com GlynOwenOffice:(770)505‐4044Mobile:(404)512‐1792E‐mail:[email protected]
Tyregrip(PrismoUSA)(EnnisPaint)
http://www.prismousa.com/ RichardJ.BakerOffice:(804)213‐0335Fax:(804)213‐0337Mobile:(804)319‐7456E‐mail:[email protected]:(678)296‐9910E‐mail:[email protected]
46
4.DATACOLLECTION
4.1LocationofStudiedHighFrictionSurfaces
AllofthetestingwasdoneinthestatesandatthelocationspresentedinTable3.
Thedistinctnessoftestingsitesandtheuniquenessofeachlocationprovidedthe
opportunitytoobtainanencompassingideaofHFSperformance.
TABLE3.HFSLocationsInvestigatedHFS State Code Location
CrafcoHFS Tennessee TN‐C SpringHill,WestboundEndSouthernparkwaytowardColumbia
Italgrip Tennessee TN‐I‐4 SpringHill,WestboundEndSouthernparkwaytowardColumbia
Italgrip Wisconsin W‐I‐1 LaCrosseHighway35NWisconsin
Italgrip Wisconsin W‐I‐2 LaCrosseHighway16WWisconsin
Italgrip Wisconsin W‐I‐3 LaCrosseHighway16EWisconsin
FlexoGrid Wisconsin W‐P LaCrosseHighway35SWisconsin
Safelane Virginia VA‐S‐1 I‐81MileMarker219S
Safelane Virginia VA‐S‐2 I‐81MileMarker239N
Safe‐T‐Grip Tennessee TN‐G SpringHill,WestboundEndSouthernparkwaytowardColumbia
Tyregrip Virginia VA‐T I‐81MileMarker210S
EP‐5* Virginia VA‐E I‐81MileMarker240S
*StandardepoxyoverlayforbridgedeckusedbyVDOT;evaluatedforcomparisononly.Figure3showsexamplesoflocationswherethestudiedproductshavebeen
applied.PicturecinthisfigureshowsabridgeapplicationbyItalgripwherethe
HFShasbeeninplacefornineyears,andpicturedpresentsaPolycarbHFSapplied
inthesameyear.Acleardifferencebetweentheconditionsoftheseproductsplaced
inthesameyearcanbenoticed.
47
a)CrafcoTennessee
b) Cargill‐EP‐5Smart‐Road
c) ItalgripWisconsin
d) PolycarbWisconsin
e) SafelaneVirginia f)SafelaneVirginia
FIGURE3.HFSLocationsinvestigated.
48
4.2MeasurementsofFrictionandTextureProperties
TextureandfrictionpropertiesfortheselectedHFSapplicationshavebeen
measuredwiththeDFTester(ASTME1969),CTMeter(ASTME2157),and
GRIPTESTER(ASTME1844);thesedevices(Figure4)arefurtherdescribedinthe
followingsections.Allfrictionandtexturemeasurementswerecollectedinsummer
monthstoavoidseasonalvariationeffectsontherecordedmeasurements.
a)CircularTrackMeter(CTMeter)
b)DynamicFrictionTester(DFTester)
c)Griptester(GT)
d)LockedWheelDevice(LWD)
FIGURE4.Datacollectiondevices.
49
4.2.1DFTESTER(ASTME1969)
TheDFTestermeasuresfrictionbyspinningahorizontaldiskfittedwiththree
spring‐loadedrubberslidersthatcontactthepavedsurface.Thiscausesthedisk’s
rotationalspeedtodecreaseduetothefrictiongeneratedbetweentheslidersand
thepavedsurface.Awatersupplyunitdeliverswatertothepavedsurfacebeing
tested.Thetorquegeneratedbytheslidingismeasuredduringthespindownand
thenusedtocalculatethefrictionasafunctionofspeed.Thisdevicemeasuresthe
dynamicfrictionofthepavementcontinuously,andtheresultsaretypically
recordedatspeedsof20,40,60,and80km/h.Forthisinvestigation,staticfriction
measurementsweretakenateightdifferentlocations:fouroneachwheelpath
alongtheHFS.Onlythetravellanewasmeasuredbecausetorecordthis
measurementthelanehadtobeclosed.Thesamefrictionpadswereusedforthe
entiresection.
4.2.2CTMETER(ASTME2157)
Thisequipmentconsistsofachargecoupleddevice(CCD)laser‐displacement
sensormountedonanarmthatrotatessuchthatthedisplacementsensorfollowsa
circulartrackhavingadiameterof284mm(11.2in.).TheCTMeterisdesignedto
measurethesamecirculartrackthatismeasuredbytheDFTester,anditreports
theMeanProfileDepth(MPD)andtheRootMeanSquare(RMS)valuesofthe
macrotextureprofiles.ThevaluesstatedinSI(metric)unitsareregardedas
standard.TheCTMeterwasusedinthisstudytomeasuresurfacetextureatthe
sameeightspotsusedforthefrictionmeasurementswiththeDFTester.
4.2.3GRIPTESTER(ASTME1844)
AFindlayIrvineGriptesterwasusedtomeasurecontinuousskidresistancealong
theinsidewheelpathofthetravellaneofthetestsections.Thissystemconsistsofa
fixedslipdevicewherethetesttireisconnectedtothetrailerwheelaxlebyachain,
allowingittomeasuretherotationalresistanceofaconstantslippingsmoothtireat
50
a15.6percentslipratio.
Measurementsaretakenatspeedsof50mphoninterstatesand40mphonother
roadways,utilizingaconstantwaterfilmthicknessof0.05cm(8.9gal/minat
80km/h).Thespeedofthetesttireis15.6percentofthespeedofthevehicle
becausethisdeviceusesaconstantslipratio.Rawdataforlongitudinalfriction
forcesandtestwheelloadsarebydefaultrecordedevery0.9m,buttheintervalcan
beadjustedaccordingtotheneedsoftheexperiment.
DuetothelocationofthetestwheelwhentheGriptesterisattachedtothevehicle,
onlytheoutsidewheelpathfrictionisrecorded(seeFigure4c).Severalrunswere
madeforeachHFSsection,andtriggeringpointsbetweeneachrunwerecompared
toaccountforpossibleerrors.
4.2.4LOCKEDWHEELDEVICE(ASTME274)
Thisfrictionmeasuringdevicerecordsthesteady‐statefrictionforceofalocked
wheelonawettedpavementsurfaceasthewheelslidesatconstantspeed.The
deviceconsistsofavehicletowingatrailerequippedwithtestswheels.Duringthe
test,whenthevehiclereachesthedesiredspeed,waterisdeliveredaheadofthetest
tireandthebrakingsystemisactivatedproducing100percentslipratio.Thewheel
remainslockedforapproximately1second,andthedataismeasuredandaveraged.
Theskidresistanceofthepavedsurfaceisreportedasskidnumber(SN)(ASTME‐
274),whichistheforcerequiredtoslidethelockedtesttireatastatedspeed,
dividedbytheeffectivewheelloadandmultipliedby100(ASTME‐274).
Thelockedwheelfrictionmeasurementsusedinthisstudywereobtainedfrom
DOTs.Informationwasobtainedonlyforalimitednumberofsections.
51
4.3CostData
ThecompaniesresponsiblefortheinstallationoftheselectedHFSsystemswere
contactedtoobtainacostestimatefortheapplicationofeachproduct.This
informationwasusedtofurtheranalyzeandcomparethecostofeachproductwith
itsperformance.HFScostvaluespresentedinTable4donotincludetrafficcontrol
andotherinstallationandsupervisioncosts.
TABLE4.TypeofAggregateandPriceforSelectedHFSProduct TypeofAggregate TotalPriceperft2
Crafco Bauxite(China‐Guyana)Granite
$3$2.25
FlexoGrid Basalt+graniteSilica
$4.5–5$2.2‐2.7
Italgrip Steelslag(patented) $2.2
Safelane(Cargill) Dolomite $6
Safe‐T‐Grip Granite $1.6
Tyregrip Calcinedbauxite(buffandgrey) $1.7
Monetaryvaluesassignedtoaccidents(Table5),injuries,andpropertydamage
wereobtainedfromtheMinnesotaDepartmentofTransportationbenefit‐cost
analysis(Mn/DOT2005).
TABLE5.CrashValuesforEconomicStudy
MN/DOTCrashValues DollarsperCrash
Fatal $3,600,000
InjuryTypeAonly $280,000
InjuryTypeBonly $61,000
InjuryTypeConly $30,000
Propertydamageonly $4,400
52
4.4AccidentData
Before‐and‐afteraccidentdatawereobtainedfromonlyonelocation:theWisconsin
DepartmentofTransportation.Accidentdatawerecollectedforaperiodofthree
yearspriortotheinstallationoftheHFStothreeyearsafterward.Itispossiblethat
someaccidentsmayhavebeenoverlookedinthisdataforseveralreasons,
including:vehicleleavingthescene,accidentnotbeingreported,exactlocation
beingincorrectlydocumentedontheaccidentreport,orbeingmissedbythe
databasesearch(Bischoff2008).
5.RESULTS
ThelocationsshowninTable3werevisitedin2008,andfrictionandmacrotexture
measurementsweretakenwiththeDFTester,CTMeterandGriptesterasdiscussed
intheprevioussection.Thissectionpresentsthemaindatacollected.
5.1FrictionandTextureDataProcessing
Theaverageandstandarddeviationwerecomputedforeachofthecollectedfriction
properties.ThevaluesobtainedfromfrictionmeasurementswiththeGriptesterat
thebeginningandendofeachdifferentpavementsectionwereomittedfromthe
datasettoaccountforpossibletriggeringerror.Inaddition,engineeringjudgment
wasusedwhenprocessingthisdatabecausejointscausedtheequipmenttojump
whenmeasuringathighspeeds,resultinginerroneousvaluesclosetothe
transitionsbetweensections.InthecaseoftheDFTesterandCTMeter,theaverage
andstandarddeviationoftheeightmeasurementsforeachHFSapplicationare
presentedinTables6and7.Thevaluesprovideanindicationoftypicalvaluesof
initialfrictionandtexturethatcouldbeexpectedofanHFSsystemonhighways.For
comparisonpurposesthetablesalsoincludevaluesoffrictionandtexturefortypical
flexibleandrigidpavementsurfaces.
53
TABLE6.FrictionMeasurementsforSelectedHFS
HFS Code Appl.Date
Friction(GN)at40mph*
Std.Dev.
Friction(DFT)at20kph
Std.Dev.
Crafco TN‐C 2008 1.05 0.05 0.98 0.02
Italgrip TN‐I 2008 1.02 0.04 1.01 0.01
Italgrip W‐I‐1 1999 0.67 0.07 0.78 0.04
Italgrip W‐I‐2 1999 0.53 0.08 0.68 0.04
Italgrip W‐I‐3 1999 0.63 0.07 0.68 0.02
Polycarb W‐P 1999 0.69 0.03 0.65 0.02
Safe‐T‐Grip TN‐G 2008 0.90 0.12 1.01 0.02
Safelane VA‐S‐1 2005 0.50 0.05 0.48 0.04
Safelane VA‐S‐2 2005 0.57 0.06 0.55 0.05
Tyregrip VA‐T 2005 0.90 0.14 1.00 0.02
EP5 Ref. 2005 0.65 0.11 0.62 0.03
SM9.5D Ref. 1999 0.77 0.01 0.82 0.03
SMA12.5 Ref. 1999 0.74 0.01 0.72 0.04
OGFC Ref. 1999 0.68 0.01 0.63 0.04
TinnedCRCP Ref. 1999 0.82 0.02 0.77 0.01
Pavementspresentedinitalicarenon‐HFSusedhereasreferencevaluesandwerecollectedontheVirginiaSmartthathasveryonlyresearchtraffic.
*Thismeasurementcorrespondsto10.14‐12.48km/hslipspeed.
Table6showsthatsomeoftheHFShaveconsiderablyhigherfrictionthanthe
conventionalsurfaces.Thedifferenceininitialfrictionbetweentheserigidand
flexiblepavementsandtheHFSsystemsemphasizestheneedforHFSsystemson
blackspotswherewet‐weathercrashesorcrashescausedbydeficientsurface
propertiesoccurfrequentlyandwhereadditionalfrictionmaybeneeded.
54
TABLE7.FrictionTextureMeasurementsforSelectedHFSHFS Code Application
DateTexture(MPD) Std.Dev.
Crafco TN‐C 2008 1.46 0.09
Italgrip TN‐I 2008 1.61 0.12
Italgrip W‐I‐1 1999 1.03 0.10
Italgrip W‐I‐2 1999 1.07 0.06
Italgrip W‐I‐3 1999 1.04 0.08
Polycarb W‐P 1999 1.07 0.24
Safelane VA‐S‐1 2005 1.53 0.16
Safelane VA‐S‐2 2005 1.56 0.20
Safe‐T‐Grip TN‐G 2008 1.57 0.23
Tyregrip VA‐T 2005 1.28 0.10
EP5 Ref. 2005 1.16 0.09
SM9.5D Ref. 1999 1.05 0.11
SMA12.5 Ref. 1999 0.91 0.13
OGFC Ref. 1999 1.58 0.09
TinnedCRCP Ref. 1999 1.17 0.09
PavementspresentedinitalicareNon‐HFSusedhereasreferencevalues.
Figure6Summarizesthedatacollectedinwhiskerboxplotsforthefrictionand
macrotextureonalloftheHFS.Table6showsthatthemacrotexturevalues
providedbytheHFSaresimilartothosemeasuredonOGFCandconsiderably
higherthanthetypicalflexibleandrigidpavementsurfaces.
55
FIGURE5.TextureandfrictionwhiskerboxplotforallHFSsystems.
Toillustratetheinfluenceofthefrictioncoefficientsonareal‐lifesituation,the
followingscenarioisproposed.A2,500‐lbvehicletravelingat65mphona
2percentdownhillgradewithabrakeefficiencyof100percentrequires210.2ftof
minimumstoppingdistanceonapavementwithafrictionof0.735DFT(average
initialfrictionofnon‐HFSpavementsfromTable6).Ontheotherhand,158.4ftis
theminimumstoppingdistanceforthesamevehicleonanHFSsurfacewitha
coefficientoffrictionof0.963DFT(averageinitialfrictionofHFSfromTable5).
0.00.20.40.60.81.01.2
DFT(FN)
HFSSystems
0.0
0.5
1.0
1.5
2.0
CTMeter(MPD)
HFSSystems
56
5.2InitialFriction–Cost
Table7summarizesthecost,initialfriction,andtexturevaluesassociatedwitheach
HFSproductforwhichenoughinformationwasobtained.Thesourceofthesecost
valuesisexplainedinSection4.2.ThepurposeofTable8istohelpagenciesidentify
whichHFSwouldbetterfulfilltheirspecificneedandatthesametimeadjustto
theirbudget.
TABLE8.PriceandInitialFrictionandMacrotextureforSelectedHFS
HFS TypeofAggregate
InitialFriction(GN)at40mph
Friction(DFT)at20km/h
Texture(MPD)
TotalPriceperft2
Crafco Bauxite 1.05 0.98 1.46 $3
Italgrip Steelslag(patented) 0.98 1.01 1.61 $2.2‐2.7
Safe‐T‐Grip* Granite 0.90 1.01 1.52 $2.2
Tyregrip CalcinedBauxite 0.90 1.01 1.28 $1.7
Safelane‐Cargill** Dolomite 0.86 1.02 1.21 $6
*Whenmeasurementswererecorded,thesystemwasnotcompletelycured.
**MeasurementswererecordedfromSmartRoadandtrafficwasassumedtobezero.
6.ANALYSIS
6.1EconomicAnalysis
Abenefit‐coststudyisaneconomicevaluationoftheadvantagesanddisadvantages
onasetofinvestmentalternatives,whereiftheratioofthebenefit‐costisgreater
thanonethealternativeissaidtobeeconomicallyjustifiable.
InthiscasethebasescenarioisaroadwaysectionwithoutanHFSapplication
(roadwaywithrigidorflexiblepavement)andthealternativeisanHFSsystem.A
57
simplifiedcost‐benefitanalysisisusedtocompareanHFSalternativewithanon‐
HFSpavementtodeterminethemostcosteffectivealternative.Thismethod
considersinitsanalysisthecostsassociatedwiththeinitialconstructionofsurface
treatment;itdoesnotincludefuturemaintenancebecauseonthesesystems
rehabilitationmeansoverlay.Thebenefitsusedintheanalysisaresafety
performanceimprovements;suchasreductionsindeaths,injuries,andproperty
damagebeforeandafterthesystemwasplaced.Theobjectiveofthiseconomic
analysisistoillustrateamethodologythatcanbeusedtoanalyzethefeasibilityof
HFSapplications.
6.1.1EstimatedHighFrictionSurfaceServiceLives
FourItalgripHFSsectionsplacedinthestateofWisconsinwerestudied.This
productandlocationwereselectedbecausehistoricalfrictionmeasurementsand
accidentdatawereonlyfoundforthisinstallation.Figure7showsmeasurementsof
frictionovertimefortwooftheselectedsurfacesamples(estimationforother
consideredlocationscanbefoundinAppendixI).Aftertrialswithdifferentmodels,
apowerregressionmodelwasselectedbecauseitexhibitedthebestbehaviorofall
HFSandalsorepresentedthephysicalwearingprocesstypicallyobserved.
Thepowertrendfittedtothedatashowedthatthevariousmaterialsdonotreach
unacceptedfrictionvalueswithintheanalysisperiod.However,basedon
engineeringjudgmentandtheobservationofthesectionsevaluatedinWisconsin,a
HFSservicelifeof10yearswasconsideredappropriate.Accordingtothedatain
Tables6and7itmaybeexpectedforthesystemtomaintainacceptablefriction
levelsafter10years;however,theravelingprocesswouldbeveryadvancedas
showninFigure3,picturec.ApplicationsW‐I‐1,W‐I‐2,W‐I‐3,andW‐Phavebeenin
servicefornineyearsandstillexhibitgoodfrictionandmacrotexturelevelsbutthe
firstthreealsoshowsignificantraveling.
58
FIGURE6.HFSwearandscuffingrate.
6.1.2ValuesforTransportationEconomicStudy
Reductioninthenumberofskid‐relatedaccidentsistheprincipalbenefitfromthe
applicationofHFS.Benefitsoccurwhenseverityornumberofcrashesisreducedin
asystemduetoroadwaysurfacepropertiesimprovement.Fortheanalysis
presentedinthisthesis,theleastsevereinjuries(typeC)forhighwayuserswere
R²=0.83
0102030405060708090100110
1 2 3 4 5 6 7 8 9 10 11
Skid
Num
ber
(SN
)
Year
HFS WI-USH 53 N Smooth40mph
Power(Smooth40mph)
R²=0.31
0102030405060708090100110
1 2 3 4 5 6 7 8 9 10 11
Skid
Num
ber
(SN
)
Year
HFS WI-STH 16 WDL Smooth40mph
Power(Smooth40mph)
59
assumedandonlypropertydamagewasconsideredforvehiclesinvolvedinthese
accidentstoevaluateHFSunderaconservativescenario.
6.1.3BenefitCost
Thebenefitoftheprojectisderivedfromcomparingthe“before”basecasehighway
accidentsthatoccurwithinthestudyareatothoseofthe“after”alternative
scenarios.ThestudyareaincludestworoadwaysectionsinthetownsofLaCrosse
andWaukesha,Wisconsin.Thebasecasescenariosaredefinedforthisthesisasthe
existingconditionsbeforetheapplicationoftheHFS,whereastheproposed
alternativescenariosaretheconditionsaftertheapplicationoftheHFS.The
analysisperiodis10years,thebaseyearis2008,andthediscountrateis4percent.
Thebenefitismeasuredasthereductionofannualnumberofcrashes,injuries,and
deathsfromthebasecasetothealternativecase.Theeconomicvaluesofthecrash
eventswereobtainedfromTable5.Thetotalpresentcostofaccidentsforthebase
andalternativecasesarecalculatedasthesumofthediscountedannualcostfound
foreachyearinthe10‐yearanalysisperiod.Thedifferenceincrashcostsbetween
thebaseandalternativearereportedasthepresentworthofbenefits.
Typicalconstructioncostswereobtainedfromthematerialsuppliersandwere
reportedinTable5.Routinemaintenancecostswereassumedtobethesamefor
thebaseandalternativescenariossincethealternativedoesnothaveasignificantly
differenteffectonmaintenanceandtheybothrequireplowing,debrisremoval,etc.
Theresultsofthebenefit‐costanalyzesforthetwostudiedareasarepresentedin
Table9andTable10.Thetablealsoshowsthebenefit‐costratiocomputedasthe
ratiobetweenthesavingsincrashcostandthecostofapplyingtheHFS.These
resultsshowthatinallfourofthestudiedsectionsthealternativeiseconomically
justifiedcomparedtothebasescenario,withbenefitcostratiosrangingbetween4
and20.
60
TABLE9.BenefitCostAnalysisforHFSLocationsinWaukesha,WisconsinWaukeshaCounty
STH16
Accidents BeforeItalgrip(perYear) incidents 1.6vehicles 2.3injured/0killed 0.67 AfterItalgrip(perYear) incidents 0vehicles 0injured/0killed 0
LaCrosseCountySTH16NBandSB
Accidents BeforeItalgrip(perYear)Incidents 3.66Vehicles 10injured/0killed 2 AfterItalgrip(perYear)Incidents 0.33Vehicles 1.33injured/0killed 0
AccidentsBenefits Vehicles‐PropertyBenefit* $85,366Injuries‐DeathBenefit** $169,550
PresentWorthBenefit $254,916 CostofHFS #ofLanes 2lanewidth 12Typicalsectionlength 400price/ft2 $2.20
TotalHFSCost $21,120
B/C 12.07
AccidentsBenefits Vehicles‐PropertyBenefit* $321,791Injuries‐DeathBenefit** $506,120
PresentWorthBenefit $827,911 CostofHFS #oflanes 4lanewidth 12Typicalsectionlength 400price/ft2 $2.20
TotalHFSCost $42,240
B/C 19.60
61
TABLE10.BenefitCostAnalysisforHFSLocationsinLaCrosse,WisconsinLaCrosseCounty
STH35NB
Accidents BeforeItalgrip(peryear)incidents 1vehicles 5.33injured/0killed 1 AfterItalgrip(Nov99Oct02)incidents 0vehicles 0injured/0killed 0
LaCrosseCountySTH53NBandSB
Accidents BeforeItalgrip(peryear)incidents 3vehicles 3.33injured/0killed 1 AfterItalgrip(Nov99Oct02)incidents 0.33vehicles 1injured/0killed 0.66
Benefits Vehicles–PropertyBenefit* $191,986Injuries‐DeathBenefit** $245,590PresentWorthBenefit $437,576
Cost #oflanes 2lanewidth 12Typicalsectionlength 400price/ft2 $2.20
HFSCost $21,120
B/C 20.72
Benefits Vehicles‐PropertyBenefit* $83,926Injuries‐DeathBenefit** $83,501PresentWorthBenefit $167,427
Cost #oflanes 4lanewidth 12Typicalsectionlength 400price/ft2 $2.20
HFSCost $42,240
B/C 3.96
62
6.2InternationalFrictionIndexforHighFrictionSurfaces.
Inordertoprovidestandardreferencevaluesforthedifferentproductsevaluated,
theInternationalFrictionIndexparameters,F(60)andSp, werecomputedusing
ASTM1960withsmallmodifications.
Table12presentstheresultsbasedontheDFTesterandCTMetermeasurements
andusingtheoriginalcoefficientsdevelopedbyPIARCandtherevisedcoefficient
presentedinChapter2andEquations(1)through(3).Inadditionthetablealso
includesthemeasuredGripnumber(GN)andthevalues“estimated”usingthe
originalandrevisedIFIcoefficients.Unfortunately,noneofthesetofconfidentscan
beusedtoaccuratelyharmonizetheDFTesterandGriptestermeasurements,since
theestimatedGripnumbersdonotmatchtheactualfieldmeasurements.This
suggeststhatmoredataonawiderrangeofpavementsurfaces,including
positively‐texturedsurfacessuchasHFS,maybeneededtoaccuratedeterminethe
harmonizationconfidents.
TABLE12.HFSFrictionMeasurementsusingtheInternationalFrictionIndex. PIARC REVISED
COEF. COEF. CODE TX Sp F(60) FR(S) FR(S) GNFIELD
TNC 1.46 145.16 0.625 0.84 0.47 1.05TNI4 1.61 158.62 0.655 0.86 1.02 1.02WI1 1.03 106.59 0.473 0.69 0.35 0.67WI2 1.07 110.18 0.427 0.60 0.14 0.53WI3 1.04 107.49 0.424 0.60 0.12 0.63WP 1.07 110.18 0.412 0.57 0.07 0.69VAS1 1.53 151.44 0.351 0.41 ‐0.19 0.50VAS2 1.56 154.13 0.392 0.47 ‐0.02 0.57TNG 1.52 150.54 0.648 0.87 1.01 0.90VAT 1.28 129.02 0.623 0.87 0.96 0.90
63
7.FINDINGSANDRECOMMENDATIONS
High‐frictionsurfaces(HFS)areincreasinglybeingconsideredforareaswhere
additionalfrictionmaybeneededbecausetheyprovidehighlevelsoffriction
withoutnegativelyaffectingotherpavementqualities,likenoiseordurability.The
reviewconductedshowedthattheproductsavailableintheUnitedStatesmarket
includeCrafcoHFS,Italgrip,FlexoGrid,Safelane,SafeTGrip,andTyregrip.Someof
theavailableapplicationsfortheseproductswereevaluatedandacost‐benefits
methodologywasproposed.
Thefieldevaluationsshowedthatmostoftheseproductsprovideveryhighinitial
levelsoffrictionandmacrotexture.Thelimitedhistoricaldataalsoshowthatat
leastsomeofthesystemscanmaintainhighfrictionvaluesafter9yearsofservice.
Furthermore,inthefewapplicationswherebeforeandaftercrashdatawere
recorded,abenefit‐costanalysisshowedthattheuseofHFSiseconomically
justified.Thereductionincrashcostis4to20timesthecostofthetreatmentsfor
theselocations.Similaranalyzesshouldbeconductedforotherproductsand
installationlocationsand/orconditionsbeforestrongconclusionscanbedrawn.
ComparisonsbetweenfrictiondatacollectedwiththeDFtesterandtheGriptester
showedthattheavailableharmonizationmodelscannotbeaccuratelyappliedto
HFS.Moreharmonizationexperimentsarerecommendedwithawiderrangeof
pavementsurfaces,includingHFSandothertypesofsurfacetreatments,to
determinetheIFIcoefficientsrecommendedbyASTM1960.
8.ACKNOWLEDGEMENTS
Thedatausedforthispaperwascollectedbyvisitingthephysicallocationsofthe
selectedinstallations.Thisexperimenthasbeenmadepossiblethankstothe
contributionsoftheTennessee,Connecticut,Wisconsin,Minnesota,andVirginia
64
departmentsoftransportation,theVirginiaTechTransportationInstitute(VTTI),
theVirginiaTransportationResearchCouncil(VTRC),theFederalHighway
Administration(FHWA),GlynOwen(Safe‐T‐Grip),NickNedas(Crafco),Robert
Schmiedlin(Crafco),AnthonyHensey(Cargill),RichardBaker(Tyregrip)andDeb
Bischoff.WilliamHobbs,OscarGonzalez,MarioCandia,KevinMcGee,andEdgarde
Leoncollaboratedwiththedatacollectionandprocessing.
9.REFERENCES
AASHTO(1991).ResistancetoDegredationofSmall‐SizeCoarseAggreagatebyAbrasionandImpactintheLosAngelesMachine.T96‐87.InterimSpecificationsforTransportationMaterialsandMethodsofSamplingandTesting.Washington,D.C.:122. AASHTO(1991).SoundnessofAggregatesbyFreezingandThawningT103‐91I.I.InterimSpecificationsforTransportationMaterialsandMethodsofSamplingandTestingTesting.Washington,D.C.:122. Adam,J.F.andE.Gansen(2001).PerformanceofPoly‐CarbFlexogridBridgeOverlaySystem.TechnicalReport.Ames,Iowa,IowaDepartmentofTransportation:10. ASTM(1998).StandardTestMethodforMeasuringPavedSurfaceFrictionalPropertiesUsingtheDynamicFrictionTester.E1911‐98.ASTM.WestConshohocken,PA:7. ASTM(2006).StandardPracticefortheAcceleratedPolishingofAggregatesUsingtheBritishWheel.D‐3319‐06.ASTM.Westconshohoken,PA:5. Bischoff,D.(2008)."InvestigativeStudyofItalgripSystem2008"(WI‐04‐08):21.Crafco,www.crafco.com/(accessed4/2008) Descornet,G.(2004).TheHERMESProject.5thSymposiumonPavementSurfaceCharacteristics.W.R.Association.Toronto,Canada,SURF:11. Flintsch,G.,E.d.Leon,McGhee,K.,AlQadyl.(2003).PavementSurfaceMacrotextureMeasurementandApplicattions.TransportationResearchBoard.WashingtonD.C.,TransportationResearchRecord.No.1860:168‐177.
65
FlexoGrid,www.poly‐carb.com/flexogrid/system.php(accessed7/2008)
Hayes,L.,M.Rosenberg,J.Abraham.(2007).MakingRoadsSafe.WorldBankGlobalRoadSafetyDecaturGeorgia,WorldBank23. Henry,J.J.(2000)."EvaluationofPavementFrictionCharacteristics."NationalCooperativeHighwayResearchProgramNCHRPSynthesisoftheHighwayPractice(291):61. Henry,J.J.andK.Siato(1983).SkidResistanceMeasurementswithBlankandRibbedTesterTiresandTheirRelationshiptoPavementTexture.TransportationResearchBoard.WashingtonD.C.,TransportationResearchRecord.No.946:38‐43. Huhta,R.S.,D.A.Meyer, P.Zelnak.(2001).TheAggregateHandbook.Arlington,Virginia. Julian,F.andS.Moler(2008)."GainingTractioninRoadwaySafety."FederalHighwayAdministrationVol.72(No.1):10.Italgrip,www.italgrip.com/usa/italgrip.htm(accessed5/2008) Kelly,T.(2008).ForensicReportoftheFailureofTyregrip.MaterialsForensicReport.PolkParkway,FloridaFloridaDepartmentofTransportation. Kuemmel,D.A.,J.R.Jaeckel,A,Satanovsky.(2000)."InvestigativeStudyoftheItalgripSystem‐NoiseAnalysis."(WI/SPR‐02‐00):20. Kuttesch,J.S.(2004).QuantifyingtheRelationshipbeweenSkidResistanceandWetWeatherAccidentsforVirginiaData.CivilandEnvironmentalBlacksburg,Virgina,VirginiaPolytechnicInstittuteandStateUniversityMasterofScience. Mn/DOT(2005)."BenefitCostAnalysisforTransportationProjects."BenefitCostAnalysisGuidance:33. N.T.S.(1999).NationalTransportationSafetyBoardAnnualReport.WashingtonD.C.NTSB/SPC‐00/03:83. Nicholls,J.C.(1997).LaboratoryTestsonHigh‐FrictionSurfacesforHighways.TransportationResearchLaboratory.England,TRL.Report176:36. Nicholls,J.C.(1998).TrialsofHigh‐FrictionSurfacesforHighways.TransportationResearchLaboratory.England,TRL.Report125:22. NTS(1999).NationalTransportationSafetyBoardAnnualReport.WashingtonD.C.NTSB/SPC‐00/03:83.
66
Reddy,V.,T.Datta,McAvoy,D.,P.Savolainen,.M,Abdel‐Aty.,S,Pinapaka.(2008).EvaluationofInnovativeSafetyTreatments.EvaluationReportOrlando,Florida,FloridaDepartementofTransportation36. Safelane‐Cargill,www.cargillsafelane.com/(accessed5/2008)
Safe‐T‐Grip,www.trafficcalmingusa.com(accessed8/2008)
Shi,C.(2004)."Steelslag:Production,processing,characteristicsandcementiousproperties."JournalofMaterialsinCivilEngineeringNo.16(No.3):7. Sprinkel,M.M.,D.Roosevelt,.Flintsch,G.,E.d.Leon.,Mokaren,D.(2008).EvaluationofCargillSafelaneEpoxyOverlay.VTRC.Charlottesville,Virginia.08‐R:45. Tyregrip,www.ennispaint.com(accessed4/2008)
Wambold,J.C.,C.E.Antle,.(1995).InternationalPIARCExperimenttoCompareandHarmonizeTextureandskidResistanceMeasurements.Paris,France,PermanentInternationalAssociationofRoadCongressesPIARC. Wambold,J.C.,J.J.Henry.,T,Yager.(2004).NASAWallopsTire/RunwayFriction.5thSymposiumonPavementSurfaceCharacteristics.W.R.Association.Toronto,Canada,SURF:19. Wambold,J.C.,T.J.Yager,JJHenry.,ZRado.(2006).AWhitePaperonCorrelationoftheGriptesterTrailertotheASTME274SkidTrailer.
67
CHAPTERIV
SUMMARY,FINDINGS,CONCLUSIONS,AND
RECOMMENDATIONS
Itisimportantthathighwayagenciesprovidedriverswithsafe,smoothrides
throughouttheyear.Itisforthisreasonthatfriction,textureandothersurface
propertiesmustbemonitoredperiodically.Roadwaysectionswithdeficientfriction
mustbetreatedtoimprovesafetyandHFSarestartingtobeconsideredasaviable
treatmentinareaswithhighnumberofskidding‐relatedaccidents.
ThethesispresentedadetailedevaluationofthemainHFSproductsavailableinthe
UnitedStatesmarket;bymeasuringtheirperformanceondifferentapplications,
underdifferentweatherconditions,andinvariouslocations(states).
Inaddition,italsopresentedeffortstocompareandharmonizetextureandskid
resistancemeasurementstakenwithvariousdevices.
1.FINDINGS
IntheprocessofevaluatingtheIFIcoefficients,discrepancieswerefoundintheIFI
valuescalculatedforthedifferentdevices:
• Thedatacollectedforthisprojectshowedthatthemodeldevelopedby
PIARCdoesnotproduceharmoniousresultsamongthedevicesusedbythe
consortiummembersintheVirginiaSmartRoadRodeoforthesurfaces
tested.
• ThissuggeststhattheoriginalcoefficientsdeterminedduringthePIARC
experimentmayneedtobeadjustedforthedevicesevaluatedbeforetheIFI
canbeimplementedintheU.S.
68
• Furthermore,itwasnotpossibletoharmonizethemeasurementsobtained
withthevariousdevicesusedinthisthesisonallthestudiedHFS.
TheevaluationofthevariousidentifiedHFSproductsandapplicationspermittedto
drawthefollowingfindings:
• TherearevariousHFSproductsavailableintheU.S.market,whichhavebeen
usedbydifferentagencies.
• ThedatacollectedforthisprojectshowedthatHFScanmaintaingoodlevels
offrictionandmacrotexturetextureforatleast9yearsofservice.
• However,someoftheevaluatedapplicationsdevelopedsignificantlevelof
ravelingafter10years.
• Thebenefit‐coststudyfoundthatatleastinareaswithhighnumberof
skidding‐relatedcrashes,HFScanbeeconomicallyjustifiabletreatments.
• Someoftheapplicationsevaluatedresultedinpresentbenefit‐costratiosof4
to20.
2.CONCLUSIONS
TheresultsoftheevaluationofthevariousidentifiedHFSproductsand
applicationssuggestedthatHFSareanappealingalternativeforareaswithfrequent
wetweatherand/orrun‐off‐the‐roadcrashes.Therefore,HFSsystemsshould
continuetobeconsideredinthepoolofavailablesafetyimprovementalternates.
Additionalapplicationandbeforeandaftercrashstudiesfordifferentapplication
conditionsmayprovideadditionalunderstandingofthebenefitsofthevarious
availablesystems.
69
3.RECOMMENDATIONSFORFUTURERESEARCH
Theuseofrecordedaccidentdataonblackspotswherefrictionisbeingmonitored
frequentlyisrecommendedtodeterminerequiredthresholdlevelsforsurface
properties’maintenanceandrehabilitation.
Itisnecessarytostudy,monitorandcorrelatetexture,frictionandaccidentdatato
predictminimumacceptablesurfacefrictionvaluesaccordingtosafetystandards.
Theexistingcorrelationbetweenaccidents,skidresistanceandgeometricdesign
parameters,likeradiusofcurvature,couldbefurtherstudied,forthereasonthata
highpercentageofaccidentsoccuroncurves.
Moreexperimentsarerecommendedwithdifferenttypesofpavementsurfaces,
includingHFSandothertypesofsurfacetreatments,todemonstratethevalidityof
theSpcoefficientsrecommendedbyASTMandalsothevalidityofusingtheDF
TesterasthestandarddevicetogatherfrictionmeasurementsfortheIFI
calculations.