Preliminary Estimation of Asphalt Pavement Frictional Properties from Superpave Gyratory Specimens and Mix Parameters

Changes in pavement texture because of temperature, moisture, and polishing reduce the available friction for vehicles to perform routine maneuvers under normal operating conditions and thereby increase the potential for skid-related accidents. Optimization of texture and frictional properties at the mix design stage requires that specimens prepared in the laboratory accurately represent the pavement surface in the field. Initial findings from an investigation of the texture and frictional properties of specimens prepared in the Superpave® gyratory compactor compared with field measurements are presented. In addition, the mix design properties that may be altered for increased friction are presented. The surfaces of the field specimens were different from their respective gyratory surfaces but were well correlated in the case of macrotexture measurements from the sand patch test. High correlation also was observed between field macrotexture and select mix properties, including the fineness modulus, voids in the mineral aggregate, percentage passing the 4.75-mm sieve, and bulk relative density. Poor correlation was observed between the British pendulum numbers recorded on unpolished field specimens and gyratory specimens, although the bottom gyratory surfaces best matched with field values. Preliminary results suggest the gyratory compactor orients the aggregate particles in a different manner from field compaction equipment. Further, the aggregate breakdown imposed by the gyratory compactor results in additional microtexture exposure not observed on newly compacted pavements in the field until trafficking removes the upper layer of asphalt cement from the coarse aggregate particles.