Investigation on the influence of conditioning time on the performance of hot-recycled mixture under ambient temperature

Abstract

Hot-recycled asphalt mixture (HRAM) has gained more attention due to its favorable performance and reuse of reclaimed asphalt pavement (RAP). However, involvement of the blending between virgin and aged asphalt may require more time to reach stability after the mixing process. It has been generally agreed that the change in degree of blending (DoB) between virgin and aged asphalt influences the performance of HRAM. Hence, it is of vital importance to reveal the development of the performances of HRAM in primary period and offer a reasonable conditioning time before conducting laboratory test to avoid over- or under-estimation. As many factors, including RAP content, aging degree of RAP and mixing procedure, may influence the conditioning time of HRAM, in this research, the HRAM with different RAP contents is taken into account. Specimens are stored at ambient environment (around 25 °C) for different days. Then, macroscopic performance tests evaluating high- and low-temperature performances as well as mechanical properties are conducted. Meanwhile, atomic force microscopy (AFM) is applied to quantify the change of nanoscale properties of HRAM under different conditioning time. The result shows that the macroscopic performances change significantly with conditioning time. But HRAM with different RAP contents exhibits distinct developing trend. Nevertheless, test results within 4 days varies significantly among all. AFM test reveals that DMT modulus increases with conditioning time, which is the reason for the performance change. Considering the time cost in laboratory testing, it is recommended for HRAM specimen to be conditioned at ambient temperature for at least 4 days before the tests. 7-day conditioning is better for HRAM with higher RAP content if time permits.