Determining the maximum permissible content of recycled asphalt pavement stockpile in plant hot-mix recycled asphalt mixtures considering homogeneity: A case study in China

In engineering practice, recycled asphalt pavement (RAP) is often obtained from various sources and is mixed and stockpiled in a disorderly manner, which is defined as a hybrid RAP. Thus, the material component of hybrid RAP shows great variability, possibly preventing the plant hot-mix recycled asphalt mixture (RHMA) from achieving stable quality. To address this problem, the German TL Asphalt-StB 07 guideline introduced an approach for evaluating the variability of RAP stockpile characteristics and subsequently determined the maximum permissible content of RAP in RHMA for different pavement layers based on the variability of the RAP stockpile. This study adopted this method in the Fuzhou–Yinchuan expressway maintenance project, Jiangxi Province, and reported a homogenization treatment measure for hybrid RAP. The results show that the material composition of hybrid RAP is characterized by significant heterogeneity in gradation and asphalt content, effectively reducing the heterogeneity of hybrid RAP, and the maximum permissible content of RAP in the binder layer can be increased by approximately 10% in the mass of RHMA. The homogenization treatment scale should comprehensively consider indices such as efficiency, cost, and expected dosage. The results of this study can serve as a reference value for determining a reasonable content of hybrid RAP in RHMA and ensuring stable RHMA quality.