Mechanical Performance and Environmental Impact Analyses of Missouri Stone Mastic Asphalt Mixtures Incorporated with Recycled Materials

With an increasing focus on improving the sustainability of asphalt mixtures, the use of recycled materials in asphalt mixtures has received significantly more attention recently. In Missouri, the incorporation of recycled materials including reclaimed asphalt pavement (RAP) and ground tire rubber (GTR) is limited to dense graded mixtures only. Missouri routinely uses stone mastic asphalt (SMA) mixtures on its interstates with high traffic for enhanced performance, and several studies have found that these recycled materials can be incorporated in SMAs without compromising their performance. This study aimed at investigating the effects of incorporating RAP and GTR in Missouri SMA mixtures. A total of 10 mixtures with varying dosages of recycled materials were designed using balanced mix design (BMD) methodology. The mechanical performance was determined by the mixture’s resistance to rutting using the Hamburg Wheel-Tracking test and cracking using the IDEAL-CT test. In addition, a disc-shaped compact tension (DC[T]) test was performed to determine thermal cracking resistance of the asphalt mixtures. Since sustainability is a key aspect of using recycled materials in asphalt mixtures, life cycle assessment (LCA) was conducted to quantify the global warming potential (GWP) of each mixture. This research showed that SMA mixture modification by 15% asphalt binder replacement with RAP proved to be the most desirable in mechanical and environmental performance. The addition of GTR did not have an adverse effect on the GWP, while the mixtures exhibited improved performance. Overall, the use of RAP and GTR in conjunction can be recommended for their implementation in SMA mixtures in Missouri.