Quantifying the Impact of Reclaimed Asphalt Pavement on the Skid Resistance of Surface Mixtures

Pavement skid resistance is critical for public safety, especially in wet-weather conditions. In Texas, as the population grows and the likelihood of wet-surface crashes and fatalities increases, the use of Surface Aggregate Classification A (SAC-A) aggregate has significantly increased each year to improve pavement skid resistance. Texas Department of Transportation specifications allow for the use of reclaimed asphalt pavement (RAP) to conserve natural resources and save costs. However, the impact of RAP on the skid resistance of the surface mixture was unknown or not quantitatively studied. Currently, all RAPs are categorized as Surface Aggregate Classification B aggregate in Texas. This study proposed a method of quantitatively evaluating the skid resistance of RAP aggregate using a dynamic friction tester (DFT). The DFT test results (friction numbers) for RAP and raw aggregate were combined according to their gradations and stockpile percentages in the mixture design, called “blended-DFT,” to predict the skid resistance of the surface mixture. Twenty asphalt mixtures with different RAP types and percentages were designed and tested to study the impact of RAP on mixtures’ skid resistance. The researchers found that adding high skid-resistant RAP increases the mixture slab DFT values, while low skid-resistant RAP decreases the slab DFT values. This confirms the potential of using high skid-resistant RAP to conserve SAC-A raw aggregate resources. A preliminary DFT threshold for RAP to be rated as SAC-A aggregate was proposed in this study.