Field Evaluation of Ultrathin 4.75-mm Hot Mix Asphalt Dense-Graded Overlay: Aggregate Properties and Pavement Surface Friction

Ultrathin overlays with 4.75-mm dense-graded hot mix asphalt (HMA) mixes are increasingly catching the attention as an effective alternative to microsurfacing or slurry seal. In the past, the State Departments of Transportation (DOTs) have been reluctant to use 4.75-mm HMA mixes because small aggregate size mixes are more prone to rutting. However, the use of ultrathin overlays in pavement preservation requires fine aggregate size mixes due to the limit of lift thickness. While some laboratory and track studies demonstrated that 4.75-mm mixes can serve well, the successful use of 4.75-mm mixes has been limited to the applications on low volume roads. In 2006, the Indiana Department of Transportation (INDOT) placed an experimental 4.75-mm HMA pavement on a high traffic volume road. Due to the poor friction performance in this pavement, INDOT initiated a study to evaluate the friction performance of 4.75-mm mixes. This study covered a total of four test sections with three different 4.75-mm mixes placed on the roads with different traffic volumes. Locked wheel trailer testing has been conducted to monitor the pavement friction for up to five years. Circular track meter (CTM) testing was conducted to evaluate surface macrotexture properties. Aggregate properties, particularly aggregate gradation and packing characteristics were examined to determine their effect on pavement surface friction. Approaches for improving pavement friction were recommended. The data and results may aid State DOTs in successful use of 4.75-mm dense-graded mixes.