Research on macro and micro performance degradation of hot in-place recycled asphalt mixtures with high RAP contents

Hot in-place recycling (HIR) technology is a cost-effective and environmentally sustainable method for pavement repair that utilizes reclaimed asphalt pavement (RAP) materials. Despite its significance in pavement rehabilitation, there is limited literature on the performance of asphalt pavements constructed using HIR. This research examines the effects of high RAP content on hot in-place recycled asphalt mixtures (HIRAM), specifically focusing on high-temperature stability, moisture damage resistance, and crack resistance. An in-situ dynamic direct tensile (ISDT) test was introduced to investigate the degradation mechanisms that influence the performance of HIRAM at a microscopic level. Additionally, a degradation model for crack resistance in HIRAM correlated with RAP content, was developed alongside macroscopic evaluations of crack performance. Results indicate that asphalt mixtures with a high RAP content (>60%) exhibit enhanced high-temperature stability and resistance to moisture damage. In comparison to asphalt mixtures with 0% RAP content, the high-temperature stability of HIRAM containing 100% RAP increased by 257.1%. Although variations in moisture damage resistance were minimal, all mixtures met regulatory standards. Crack resistance was primarily influenced by the content of RAP, when RAP content exceeded 90%, the fracture energy ( G f ) decreased by 66.1% to 73.4%. The results obtained from the ISDT micro-experiment and Semi-Circular Bend (SCB) mixture tests closely align, with the correlation coefficient of the developed model for cracking resistance decay in relation to RAP content reaching 0.9932. Furthermore, the ISDT test has been validated as an effective method for assessing the cracking resistance of HIRAM with elevated RAP content at a micro-scale level.