Recycling potential of used crumb rubber for second-round asphalt modification

Abstract

Crumb rubber (CR) has been widely applied to advance sustainable pavement technology. Two major industrialization processes (dry and wet) are dominant in the practice. With the increased maintenance needs of CR modified asphalt mixture , there is a salient engineering issue that if the aged CR can function as a “tea bag” for reusing purpose in the recycling of pavement material . To cope with this issue, this study innovatively focuses on two perspectives: property investigation of the asphalt binder modified by the aged CR, and further modification effect evaluation of the aged CR utilizing the liquid phase of the modified binder . Specifically, aged CR agents are prepared by two approaches that simulate the long-term aging of CR after the dry or wet process, respectively. Pen60/70 and five types of asphalt binder samples with the addition of processed CR are prepared to test, evaluate, and compare. The liquid phase samples of the asphalt binder incorporating different CR agents are prepared for further modification effect evaluation. Conventional engineering properties tests and rheological tests are also conducted. Test results show that compared to pressure aging vessel (PAV) aging, ultraviolet (UV) aging has less impact on CR. The coupling effect of the initial modification and PAV aging can significantly undermine binder's engineering performance. The rheological test results and modification efficiency analysis demonstrate that initial modification or the aging process limits the potential of the further utilization of aged CR. The results of this study can prompt the understanding of aged CR and benefit its industrial application. • The rubberized asphalt samples modified with aged CR were prepared and evaluated. • The modification effect of aged CR was further evaluated by the liquid phases. • The aged CR generated by UV aging or PAV aging can still be an effective modifier. • The aged CR recycled from PAV aged CRMA is not suitable for re-modification.