Development of surface friction guidelines for LADOTD.

Final report; July 2009-June 2011.PDFTech ReportFHWA/LA.11/485LTRC Project number: 09-2BSIO number: 30000119Friction courseSurface course (Pavements)Friction testsRolling frictionRolling resistanceAggregatesAggregate mixturesPhysical propertiesTexturePolishing (Aggregates)Rolling contactMix designMaterials selectionLouisianaLouisiana Transportation Research CenterWu, ZhongKing, BillLouisiana Transportation Research CenterLouisiana. Dept. of Transportation and DevelopmentUnited States. Federal Highway AdministrationNTL-HIGHWAY/ROAD TRANSPORTATION-MaterialsNTL-HIGHWAY/ROAD TRANSPORTATION-Pavement Management and PerformanceNTL-HIGHWAY/ROAD TRANSPORTATION-DesignUS Transportation CollectionThe main objective of this study was to develop a Louisiana pavement surface friction guideline that considers polished stone value (PSV) and mixturetype alike in terms of both micro- and macro- surface textures. The polishing and texture properties of aggregates were characterized using the BritishPendulum, Micro-Deval and Aggregate Imaging System (AIMS). Asphalt mixture slabs were fabricated with different combinations of two aggregatesources (sandstone and limestone) and four mixture types and polished by a three-wheel accelerated polishing device developed by the National Center forAsphalt Technology (NCAT). The surface frictional characteristics of each slab were measured by Dynamic Fiction tester (DFT) and Circular TextureMeter (CTM) at various pre-determined polishing cycles. In addition, an inventory dataset of field friction number (FN) measurements was obtained fromthe LADOTD\ue2\u20ac\u2122s Materials Laboratory and analyzed in this study to determine the effects of traffic loading, aggregate and mixture types on the measuredFN values.The laboratory results indicated that the accelerated polishing device used in this study performed just as the expectation; i.e., as the polishing cycleincreases, the measured frictional property of testing slab surface decreases. It was found that the DFT measurements were fairly sensitive to the coarseaggregate types (related to micro-texture) used in mix design, but were not very sensitive to different mix types or aggregate gradations (related to macrotexture).The analysis of CTM measured Mean Profile Depth (MPD) results confirmed a strong relationship between MPD and mixture type, indicatingMPD does reflect well of surface macro-texture. Because friction resistance of an asphalt mixture should account for both micro- and macro-texture, theInternational Friction Index (IFI) friction numbers, the F(60), were determined based on an IFI model using measured DF20 (the DFT measurement at afriction speed of 20 mi/hr) and MPD values for each slab tested. Further analysis of F(60) results generally indicated that an open-graded friction coarse(OGFC) mix type considered in this study had the highest friction resistance due to its largest surface macro-texture (or MPD values), followed by thestone matrix asphalt (SMA) mix type, and then by the two Superpave mix types considered (a 19-mm Superpave Level-II mix, a 12.5-mm SuperpaveLevel-II mix). The F(60) results also indicated that a selected sandstone type (AB13) with a high polishing resistance (PSV>37) performed significantlybetter in terms of mixture friction resistance than a selected limestone (AA50) with an PSV of 31. Mixtures using an aggregate blend of 30 percent ofselected sandstone and 70 percent of the limestone tended to have a better surface friction resistance than those with 100 percent of the limestone. Thisobservation demonstrates that blending of low and high friction aggregates together can possibly produce an asphalt mixture with an adequate field frictionresistance.The analysis has led to the development of a set of prediction models of mixture frictional properties, and a laboratory mix design procedure thataddresses the surface friction resistance of an asphalt mixture in terms of both micro- and macro- surface textures. The developed frictional mix designprocedure allows estimating a friction-demand based, design SN value for an asphalt mixture during the mix design stage