Study on the Modification Mechanism of Warm Asphalt Rubber Based on Stage-Extraction Method

To investigate the performance impact mechanism of warm asphalt rubber (WAR), 2 types of asphalt rubber (AR) and 4 types of warm asphalt rubber were prepared by using 70# base asphalt, 2 types of warm mixing agents, and 2 grain sizes of crumb rubber modifier. Liquid phase and insoluble crumb rubber modifier for prepared asphalt samples were obtained by the solid-liquid phase separation. The staged extraction method was innovatively employed to systematically extract components in the insoluble crumb rubber modifier blending zone layer by layer. Through experiments, the study established the connection between the preferential absorption of crumb rubber modifier and high-and medium-temperature rheological properties represented by asphalt rubber and clarified the modification mechanism of warm asphalt rubber. Test results indicate that the improvement of asphalt rubber’s high-temperature rutting resistance and low-temperature cracking resistance performance are attributed to the particle effect generated by insoluble crumb rubber modifier in asphalt and the modification effect of the soluble components of crumb rubber modifier. The improvement of fatigue resistance at medium temperature and the increase in viscosity of asphalt rubber is mainly attributed to the particle effect generated in the insoluble crumb rubber modifier. Different types of thermal mixture have different effects on the rheological properties of asphalt rubber. The addition of the organic warm mix additive is more significant in enhancing the high-temperature resistance to rutting and medium-temperature resistance to fatigue performance of asphalt rubber. The addition of the chemical warm mix additive proves to be more effective in improving the low-temperature resistance to cracking performance of asphalt rubber. The lighter components with smaller relative molecular mass in the asphalt rubber liquid phase are more easily absorbed by the crumb rubber modifier into its blending zone. The organic warm mix additive has almost no significant effect on the preferential absorption of crumb rubber modifier, while the addition of the chemical warm mix additive not only reduces the proportion of large relative molecular mass components in the liquid phase but also weakens the preferential absorption of crumb rubber modifier. The preferential absorption of crumb rubber modifier is beneficial for improving the high-temperature and fatigue resistance properties of asphalt rubber.