Skid-resistance durability and wear/polish-resistance behaviors of ultra-thin friction course designed based on the differential polishing of aggregates

To improve the skid-resistance durability of asphalt pavements in a cost-effective manner, this study introduced a differential-polishing principle based on blending various aggregates. SMA-5 ultra-thin friction courses (UTFC) were prepared using mineral aggregates consisting of 88# calcined bauxite and limestone blended in six proportions. Long-term simulated traffic polishing tests were performed on six types of UTFC surfaces in the laboratory. Direct skid-resistance indexes, BPN20 and μ80, were used to evaluate skid resistance at low and high velocities after different polishing cycles, respectively. Surface texture evolution during long-term polishing was analyzed using bearing area ratio, mean profile depth, and fractal dimension D. Additionally, an attenuation prediction model for skid resistance was developed. Aggregate mechanical properties affecting skid-resistance durability of UTFC were investigated through grey correlation analysis. The results show that a significant differential-polishing effect was generated during long-term polishing due to large differences in the two aggregates’ wear/polish resistance, which can effectively reduce the attenuation rate of skid resistance of UTFC and improve skid-resistance durability by decreasing wear loss of UTFC surface aggregate and forming texture structure difference between aggregates to maintain rough surface texture. The reasonable blending proportion of 88# calcined bauxite was determined to be 40%–60% of the mineral aggregate mass. It was also found that the developed predictive model can reflect the attenuation law of skid resistance, and PSV and LAA loss of aggregates are well correlated with the skid-resistance durability of UTFC.