Laboratory investigation and statistical analysis of the rutting and fatigue resistance of asphalt mixtures containing crumb-rubber and wax-based warm mix asphalt additive

Recent studies show that using crumb rubber modifier (CRM) improves the mechanical and rheological properties of asphalt samples. However, the higher viscosity of rubberized binders increases the production temperatures of resulting mixtures. Using Warm Mix Asphalt (WMA) technology in combination with rubberized binders is a practical solution to alleviate this problem. However, mechanical characteristics of rubberized warm mixtures should be further analyzed to determine the effects of warm additives on the performance of asphalt mixtures. This study was performed to investigate the effects of an organic WMA additive, Slack wax (SW) (2%, 4%, and 6% by weight of binder), upon rutting and fatigue resistance of rubberized asphalt mixtures (15% and 20% CRM by binder weight). Further, a statistical analysis was conducted to define the possible relationships between fatigue life and three mechanical factors: toughness index (TI), resilient modulus, and indirect tensile strength (ITS). The results of the dynamic creep test indicated that both CRM and SW increased the flow number of asphalt samples yielding more resistant mixtures against rutting distress. The wheel tracking test results were consistent with the dynamic creep test. According to the indirect tensile fatigue test, the addition of SW was effective in improving the fatigue life of both control and rubberized asphalt specimens under two studied stress levels. TI values derived from the ITS test showed that rubberized warm mixtures can significantly increase the flexibility and energy absorptivity of asphalt mixtures. The results of bivariate correlation analysis indicated a direct relationship between the fatigue life-M-r and fatigue life-TI parameters. The significant values of correlation demonstrate that TI value derived from a cheap, easy, and fast ITS test is a practical parameter to predict the fatigue life of rubberized warm mixtures.