Performance of Alkali-Activated Fly Ash Stabilized High Percentage RAP Aggregates as a Pavement Base Course: Laboratory and Field Perspectives

This study aims to assess the long-term performance of fly ash (FA) stabilized reclaimed asphalt pavement (RAP) when utilized as a base course in a full-scale experimental test section. The design mixture for the base course was prepared using an alkali-activated FA-stabilized RAP base (FRB) mixture comprised of 60% RAP, 40% Virgin Aggregate (VA), and 20% FA by weight employing a replacement method. An array of laboratory experiments, including unconfined compressive strength, resilient modulus, and durability tests were performed on FRB mixtures. The test results showed that the alkali activation using the liquid alkaline activator (LAA = Na₂SiO₃:NaOH) has significantly improved the mechanical strength, stiffness and durability of the mixtures. After that, an experimental test section was designed and constructed on a state highway to evaluate the long-term performance under actual traffic and climatic conditions using horizontal inclinometers and surface profiles. No sign of any distress was observed throughout the monitoring period of 5 years. A comprehensive cost–benefit analysis was performed, which demonstrated that the FRB section could reduce the overall construction cost by approximately 17% while decreasing the total pavement thickness by about 21%. The embodied carbon and global energy potential were calculated for the FRB section and compared the data with equivalent cement-treated base courses. The embodied carbon for the FRB section was estimated to be 30% less than the equivalent cement-treated RAP base for a comparable mechanical strength.