Effect of Blending and Curing Conditions on the Storage Stability of Rubberized Asphalt Binders

Crumb rubber modifier (CRM) binders easily suffer from instability at high temperatures, with many suggestions being developed to evaluate their storage stability. However, much uncertainty around CRM binders still exists regarding the relationship between mixing methods and experiments in order to calculate the separation index. In this study, a laboratory investigation into how CRM binders behave regarding storage stability using different mixing methods and experiments was conducted. The CRM asphalt binder in this study was prepared through a wet mixing process with the addition of 5% and 10% crumb rubber modifier (by weight) at 200 °C. The three main modification methods were method A: high-shear mixing (8000 rpm) for 2 h, method B: low mixing (300 rpm) for 8 h, and method C: high-shear mixing (8000 rpm) for 2 h + low mixing (300 rpm) for 6 h. In addition, the effect of separation index (SI) on storage stability was assessed, measuring viscosity, G*/sin δ, and percentage recovery. In general, the results of this study revealed that method C appeared to have the most prominent effect on decreasing the difference between the values of the top and bottom parts; the results for 5% CRM using method C showed that there were no differences among the values for the top, middle, and bottom parts; from the MSCR test, method C was effective in decreasing the difference between the values of the top and bottom parts. It was observed that method C improved storage stability. However, the results for percentage recovery were relatively higher than the separation index when using rotational viscosity and G*/sin δ.