Effect of wax-based warm mix additives on fatigue and rutting performance of crumb rubber modified asphalt

Abstract

Nowadays, the use of crumb rubber modified asphalt (CRMA) has gained popularity among the contractors and construction agencies due to the addition of crumb rubber in bitumen, which can increase the life span of asphalt pavement. The experimental studies have also shown that CRMA binder can improve some mechanical properties of asphalt mixture such as rutting and fatigue resistance. However, as a result of higher viscosity in the CRMA binders, higher mixing and compaction temperatures are required. So, to overcome this problem, the use of warm mix asphalt (WMA) additives accompanied with rubberized binders has been proposed. Since it is believed that crumb rubber modifier (CRM) can improve the rheological characteristics of bitumen; therefore, there is a need to more investigate the properties of CRMA binder modified with WMA additives to ascertain its proper usage in pavement construction. In this regard, the main objective of this study was to investigate the effects of two wax-based additives, as Slack wax and Polypropylene wax, on fatigue and rutting resistance of the rubberized binders modified with 15% CRM. Accordingly, the obtained results indicate that both wax-based additives have the ability of reducing the viscosity of the rubberized binders at high temperatures. Also, 2% of Polypropylene wax increased the high temperature performance of rubberized binder up to one grade. According to the results of multiple stress creep recovery (MSCR) test, the lower Jnr3.2 and higher R% values represent that Polypropylene wax can improve the rutting resistance of the rubberized binder, so that the samples containing 2% of Polypropylene wax have a higher rutting resistance than the 4% and 6% samples. Moreover, the Linear Amplitude Sweep (LAS) test’s results indicated that CRMA binders containing 6% of Slack wax have considerably higher fatigue life compared to the control rubberized binder, particularly in low strain levels.