Surface activation of scrap tire crumb rubber to improve compatibility of rubberized asphalt

The management of scrap tires became a great concern nowadays. Crumb rubber (CR) derived from the grinding of scrap tires has successfully been used as modifier for the paving asphalt towards sustainability, and the end product was generally known as rubberized asphalt. Although rubberized asphalt was considered as a green paving material with favorable engineering benefits, it suffered from poor compatibility that severely limited its application. This incompatibility issue was essentially caused by the great differences in chemical nature (molecular size and polarity) and physical features (density and solubility) between CR and asphalt matrix. One solution to this problem was the surface activation of CR, which aimed to modify the chemical and/or physical characteristics of the CR surface. By far, the practical surface activation methods mainly included pre-reaction, oxidization, grafting, polymer coating, and solution soaking as chemical methods as well as plasma treatment and gamma radiation as physical methods. Meanwhile, concerning the limitations of present technologies, recommendations for future studies focusing on this issue were provided.