An Approach to Maximize the Frictional Performance of Asphalt Mixtures by Integrating a Low Percentage of High-Friction-Resistance Aggregates

Skid resistance is crucial for the safety of road users; however, it has received little consideration during the asphalt mixture design stage. This study focuses on improving the frictional performance of asphalt mixtures comprising low-friction (e.g., limestone) aggregates. The main objective of this study is to identify the mix parameters that primarily control asphalt mixtures’ frictional performance. To achieve this objective, an experimental plan was devised and executed to quantify various material-related (binder grade and aggregate type), mix design-related (binder content, aggregate gradation, asphalt mixture type, and aggregate types in gradation portions), and construction-related (e.g., compaction effort) parameters on the frictional performance of mixtures. The mixture’s frictional performance was evaluated using a three-wheel polishing device (TWPD) and a dynamic friction tester (DFT) by varying the material, mix design, and construction parameters. The influence of binder grade, binder content, aggregate gradation, asphalt mixture type, and air void percentage on the mixture’s frictional performance was found to be negligible, while the aggregate type showed a profound effect on the mixture’s frictional performance. A more detailed study on the portion of the gradation contributing the most to frictional performance revealed that the aggregate passing through the 4.75 mm sieve and retained on the 2.36 mm sieve is the principal controlling parameter, due to its higher surface area compared to coarser aggregates. Although aggregates smaller than 2.36 mm sieve size have a higher surface area, their effect on frictional performance is less significant due to their loss during the polishing process, their relatively small proportion in the mix, and their embedment into the binder matrix.