High RAP Content Surface Mixtures: Effects of RAP and Virgin Binder Consistency/Variability During Production on Performance and Balanced Mix Design Using Field Pilot Projects in Massachusetts

The Massachusetts Department of Transportation (MassDOT) currently limits reclaimed asphalt pavement (RAP) in surface mixtures to 15%. To improve sustainability and reduce costs, MassDOT initiated pilot projects using higher RAP content. This study evaluates the effects of RAP and virgin binder variability during production on the performance of Superpave High RAP Surface Course (SSC-HR) mixtures. Two asphalt plants produced mixtures with RAP contents of 25% and 28%, sampled across multiple production dates and seasons. Virgin binders, RAP binders, and recovered binders were tested for their rheological properties, whereas RAP and mixtures were evaluated for binder content and aggregate gradation. Balanced performance was assessed according to rutting, intermediate-temperature cracking, and low-temperature cracking. FlexPAVE ^™ simulations quantified long-term rutting and fatigue performances. The results showed that production variability influenced binder stiffness and relaxation properties; however, mixtures meeting proposed tolerances for gradation, binder content, and RAP binder performance grades consistently achieved balanced performance. Specifically, SSC-HR mixtures demonstrated rutting and cracking performance comparable to that of conventional surface mixtures, with no significant loss in predicted fatigue life or increase in rutting according to mechanistic simulations. The findings demonstrated that incorporating cracking performance tests into the design and acceptance process is critical to ensure balanced performance. Overall, the results supported the feasibility of increasing RAP contents beyond current limits while maintaining performance, provided that variability is controlled through appropriate material tolerances and performance-based design criteria.