Long-term skid resistance of asphalt surfacings: Correlation between Wehner-Schulze friction values and the mineralogical composition of the aggregates

This work focuses on the relation between the mineralogical composition of aggregates and their capacity to generate adequate friction between the road surface and the tyre after the polishing action of traffic. Three different types of aggregate namely greywacke, granite and limestone were used in the study. Petrographic examination of the aggregates was carried out using optical microscopy. The Wehner-Schulze apparatus was used to determine the evolution of friction with polishing cycles of both aggregates and asphalt specimens. A new aggregate hardness parameter was introduced based on the mineralogical composition and the hardness of the individual minerals. This hardness parameter was then related to friction coefficients measured on aggregate specimens after 180.000 polishing cycles. Initial results indicated that this new aggregate hardness parameter is a good indicator of the capacity of an aggregate to retain good friction levels. Changes in the microtexture of the aggregate during polishing were also analysed using a confocal microscopy technique. Microtexture measurements confirmed different levels of polishing for the different types of aggregates.