Investigating RAP Dispersion and Its Effect on the Performance of Recycled Hot-Mix Asphalt Mixtures

The migration of reclaimed asphalt pavement (RAP) mastic into the recycled hot-mix asphalt (RHMA) mixture system during the hot-mix process results in varying dispersion degrees of RAP aggregates within RHMA, impacting its durability. This study aimed to investigate the impact of hot mix parameters on RAP dispersion and RHMA performance. The dispersion degree of RAP aggregates in RHMA was determined through slicing and digital image processing. The influence of hot mix parameters on RHMA performance was assessed through rotary compaction, Marshall, moisture-induced sensitivity, and low-temperature bending beam tests. The correlation between the RHMA performance and RAP dispersion degree was analyzed by employing the Pearson correlation coefficient. The findings show that higher RAP content reduces the RAP dispersion degree, whereas the opposite trend was observed for the RAP preheating temperature, RHMA mixing temperature, and RHMA mixing duration. Improving the RAP dispersion degree in RHMA decreased the compacted energy index and air voids in RHMA, thereby enhancing the Marshall stability, moisture stability, and low-temperature crack resistance of RHMA.