Study on the factors affecting temperature and workability during the mixing process of hot in-place recycled asphalt mixtures (RHMA)

ABSTRACT The temperature characteristics and workability of Recycled Hot Mix Asphalt (RHMA) are critical determinants of pavement construction quality. This study investigates these factors by conducting an orthogonal mixing experiment, considering four variables-aggregate gradation, asphalt content, mixing time, and preheating temperature of reclaimed asphalt pavement (RAP) – each at four levels, with RAP contents of 30%, 40%, and 50%. An infrared thermal imager is employed to measure the temperature, and the workability evaluation index is calculated based on the motor’s output power. The analysis revealed that higher RAP content adversely impacts both heating efficiency and workability. RAP preheating temperature emerged as a dominant factor, significantly affecting temperature uniformity and the final mixing temperature. Insufficient RAP preheating can be mitigated by overheating new aggregate to compensate for the temperature deficit. The relative influence of factors on low-temperature regions follows the order: RAP preheating temperature > mixing time > asphalt content > gradation index. With increasing RAP content, the influence of RAP preheating temperature on RHMA workability becomes more pronounced, while the remaining factors influence workability in the order: mixing time > gradation index > asphalt content. This study offers valuable insights into the temperature and workability dynamics of RHMA during the hot-mix process, providing a theoretical basis for optimizing mixing parameters and improving construction quality.