Comparison of Fatigue Resistance of HMA and WMA Mixtures Modified by SBS

This study aims to investigate the effect of warm mix asphalt (WMA) additives on fatigue life of unmodified and SBS- modified asphalt mixes. Two different WMA additives, including Aspha-min and Sasobit were used to fabricate WMA specimens. Fatigue test was performed on warm polymer modified asphalt (PMA) by indirect tensile test on two stress levels (300,450 kPa) at 20 °C and fatigue life was compared with PMA mixture. Also, indirect tensile strength (ITS) test was performed to determine the moisture susceptibility of warm PMA. In order to evaluate the fatigue performance of warm mix asphalt (WMA) mixtures in comparison with hot mixture asphalt (HMA), four-point flexural beam test was employed. Four- point flexural beam test was conducted at four strain levels (650, 800, 1000 and 1200 μɛ) and frequency of 7.5 Hz at 20 °C. According to the test results, it was shown that warm PMA mixtures prepared by Aspha-min and Sasobit, have less fatigue resistance in comparison with PMA mixture. Also the fatigue resistance of warm PMA mixture made by Sasobit is greater than fatigue resistance of warm PMA mixture made by Aspha-min. Based on the ITS test results, warm PMA with Sasobit additive and PMA achieved the desirable tensile strength ratio (TSR) criterion (80%) but warm PMA Aspha-min had TSR lower than 80%. Also fatigue life determination based on 50% reduction in initial stiffness showed that the fatigue life of HMA mixture is less than WMA mixtures at lower strain levels whereas it was comparable with warm mix asphalt at higher strain levels.