Impact of RAS on Environmental and Engineering Performance of Stone Mastic Asphalt

Abstract: Evaluating the integration of Recycled Asphalt Shingles (RAS) into asphalt mixtures is crucial for sustainable road construction practices. It reduces the demand for virgin materials, lessening environmental impacts and conserving natural resources. However, improper use of RAS in asphalt mixtures in the past has led to poor pavement performance. As a result, several state departments of transportation (DOTs), including the Oklahoma Department of Transportation (ODOT) have prohibited the use of RAS in their mixes. Nevertheless, multiple state DOTs as well as highway agencies (e.g. Texas DOT, Missouri DOT, Illinois Tollway) continue to successfully use RAS in their asphalt mixtures; pavement structures constructed using these mixes continue to perform adequately. This means that if an agency adopts rigorous quality control practices for RAS and diligently incorporates the material into their asphalt mixtures, it is possible to derive adequate performance from those mixes. Also, with the development of Balanced Mix Design (BMD) approach, it is now possible to accurately ascertain if a mix is good performing at the mix design stage, based on the mix’s performance under different performance tests.

An ongoing study at Oklahoma State University is exploring the use of RAS in Stone Mastic Asphalt (SMA). The focus is on ODOT-approved SMA mix designs, examining how varying RAS content (2%, 3%, and 5%) impacts critical performance indicators such as cracking tolerance and rutting, as assessed through the IDEAL Cracking Test (IDEAL-CT) and Hamburg Wheel Tracking Test (HWTT), respectively. Conventional superpave volumetric parameters such as Voids in Mineral Aggregates (VMA) and Voids Filled with Asphalt (VFA) are also being monitored to assess how RAS incorporation into the mix affects mix volumetrics. Besides testing the mixes for engineering properties, this project will also conduct Life Cycle Assessment (LCA) to quantify the environmental impacts of incorporating RAS into SMAs. This paper will present detailed findings from this study, and will will recommend suitable approaches for incorporating RAS into SMA mixes to ensure adequate pavement performance under vehicular as well as environmental loading.