WMA Overlay Optimization Based on the LTPP Database: Using the RSM Method

Abstract

This study investigates the field performance of Warm Mix Asphalt (WMA) road overlays containing various amounts of RAP and binder. Rutting, the International Roughness Index (IRI), and transverse, longitudinal and alligator cracking are the key parameters considered here. Our research is based on a Specific Pavement Study-10 experiment (SPS-10) conducted in nine states of North America (eight in the USA and one in Canada) that included 31 road sections in dry and wet regions. Road overlays were evaluated 1 and 4 years after their placement in terms of anti-cracking behavior and were compared with the pre-treatment status of the road. The best rutting resistance occurred at 15% and 12% RAP in dry and wet regions, respectively. For IRI, 30% and 0.0% RAP were the best for dry and wet regions as well. The maximum longitudinal crack recovery rates were found at site 3 (BA01, Arizona; dry region) and site 26 (AA65, Missouri; wet region), with RAP contents of 20% and 36%, respectively. In addition, alligator cracking did not occur post-overlay, so optimal RAP and binder contents cannot be suggested. The greatest improvements were found at site 15 (AA01, Washington state; dry) and site 30 (AA63, Oklahoma; wet). The response surface method (RSM) was also developed to explore the optimal models for RAP and selection of binder contents to minimize the rutting, IRI, and transverse and longitudinal crack lengths.

Keywords

• WMA overlay
• rutting
• international roughness index
• transverse cracking
• longitudinal cracking
• response surface methodology