Effect of design parameters on low-temperature cracking resistance of recycled hot-mix asphalt mixtures

This study aims to investigate the effects of different design parameters on the low-temperature crack resistance of recycled asphalt mixtures and to provide design guidance for recycled asphalt mixtures. Three material composition factors (reclaimed asphalt pavement (RAP) content, gradation type, and asphalt content) and four mixing process factors (RAP preheating temperature, mixing duration, mixing temperature, and mixing sequence) were considered. Using a single-factor controlled variable method, AC-20 recycled asphalt mixture was designed to study low-temperature crack resistance through a semi-circular bending (SCB) test, the significance of the effects of different factors was analyzed using the orthogonal test, and the fracture surface morphology was observed. Results show that both material composition and mixing processes impact the low-temperature crack resistance of recycled asphalt mixtures. Specifically, lower RAP content, higher asphalt content, higher mixing temperature, longer mixing duration, and mixing sequence I favor improved low-temperature crack resistance. Gradation type and RAP preheating temperature showed non-linear effects, peaking before declining. Material composition, especially asphalt content, has a more significant effect on the low-temperature crack resistance than mixing process factors. To achieve optimal low-temperature crack resistance, it is recommended to optimize the material composition of recycled asphalt mixture and control the RAP preheating temperature to 110 °C, maintain laboratory mixing duration of at least 150s, set the mixing temperature to at least 160 °C, and follow mixing sequence I.