Aging behavior and microscopic characteristics of modified asphalt using different pretreated crumb rubber

Pretreatment of crumb rubber (CR) can significantly enhance its interfacial compatibility with asphalt and improve the workability of crumb rubber modified asphalt (CRMA). However, the structure and internal composition of pretreated CR are inevitably altered, the difference in aging resistance of CRMA with different pretreated CR need to be systematically studied. In this research, CR was pretreated by microwave activation, waste cooking oil (WCO) swelling and alkali solution soaking respectively, and corresponding modified asphalt namely CRMA-activated, CRMA-swelled and CRMA-soaked were prepared. Then, laboratory thin-film oven test (TFOT) and pressurized aging vessel (PAV) were carried out on different types of binders, the rheological properties of different CRMAs before and after aging were systematically investigated. Afterwards, the thermal stability, functional group and microstructures of all samples were also analyzed, and possible anti-aging mechanism of CRMA was proposed. The experimental results indicate that CRMA-activated and CRMA-soaked have more significant viscous behavior after aging compared with untreated CRMA. Also, the increments of their sulfoxide index and carboxyl index before and after aging are lower than that of untreated CRMA. Moreover, both activated CR and soaked CR enhance the adsorption capacity to the light components of asphalt, and therefore their anti-aging ability are improved. Unfortunately, the temperature sensitivity of CRMA-swelled shows the largest reduction before and after aging. During aging, both the asphalt light components and free WCO molecules are volatilized and oxidized more easily, which causes the deterioration of its aging resistance and low temperature performance. Overall, The findings are instructive for the optimization of CR pretreatment method and high-performance clean application of CRMA.