Balanced RAP/RAS Mix Design and Performance Evaluation System for Project-Specific Service Conditions

The use of reclaimed asphalt pavement (RAP) and recycled asphalt shingles (RAS) can significantly reduce the increasing cost of hot-mix asphalt paving, conserve energy, and protect the environment. However, the premature cracking problem has been a serious concern. This report presents the latest work on RAP/RAS mix design and performance analysis including field performance of a variety of RAP/RAS test sections around Texas, and the proposed RAP/RAS mix design and performance evaluation system for project-specific service conditions. RAP/RAS mixes can have better or similar performance than virgin mixes if they are well designed with balancing both rutting/moisture damage and cracking requirements. Cracking performance of RAP/RAS mixes is influenced by many factors, such as traffic, climate, existing pavement conditions for asphalt overlays, and pavement structure and layer thickness. It is obvious that a single cracking requirement does not apply to all asphalt overlay applications. Instead, a project-specific service conditions based mix design system should be developed. Based on the relationship between Overlay Test (OT) cycles and fracture properties (A and n) established under this study, a balanced RAP/RAS mix design and performance evaluation system for project-specific service conditions is proposed, and it includes a balanced mix design procedure and a performance evaluation system in which the Hamburg wheel tracking test and associated criteria are used to control rutting/moisture damage and the OT, and the required OT cycles determined from S-TxACOL cracking prediction with consideration of climate, traffic, pavement structure and existing pavement conditions. Additionally, the impacts of soft binder on engineering properties of RAP/RAS mixes in terms of dynamic modulus, HWTT rut depth, and OT cycles are investigated. The test results clearly indicated that the use of soft and modified asphalt binder (i.e., PG xx-28, PG xx-34) can effectively improve cracking resistance of RAP/RAS mixes without sacrificing much rutting/moisture damage resistance. Dynamic modulus is not a good indicator as cracking resistance of RAP/RAS mixes. Researchers highly recommend that the proposed RAP/RAS mix design and performance evaluation system for project-specific service conditions be implemented statewide.