Stage-aging characteristics and stages division of crumb rubber modified asphalt binder

Currently, the aged crumb rubber-modified asphalt binder (CRMA) pavements have recycling demands; however, the understanding of the aging behavior of CRMA remains limited. Furthermore, few studies have been conducted to divide the aging stage of CRMA, which is an essential basis for the study of recycling. To solve the above problems, this study aims to analyze the stage-aging characteristics and divide the aging stages of the CRMA to understand better the aging and recycling mechanism of CRMA. The evolution characteristics of the rheological performance of aged CRMA were assessed by high-temperature performance indicators. In addition, thermal gravimetric analysis (TGA) is employed to investigate the degradation degree of crumb rubber modifier (CRM). Finally, the rheological-performance results are combined with the TGA results to divide the aging stages. The results demonstrate that the CRM in CRMA degrades in aging, which shows an initial rapid degradation, then slows down. The process of CRM degradation is accompanied by changes in CRM composition; the natural rubber content of CRM decreases the most significantly, followed by synthetic rubber and filler. The evolution of the properties of aged CRMA is characterized by stages due to CRM degradation, and the CRMA is divided into three aging stages. In addition, the gray correlation entropy analysis demonstrates that the MSCR test is more sensitive to the degradation of CRM in CRMA; it can be used to characterize the stage-aging process of CRMA. In summary, this study's results might fill a significant gap in understanding the aging mechanism of CRMA and provide the basis for recycling the aged CRMA.