Effect of MSCR Percent Recovery on Performance of Polymer Modified Asphalt Mixtures

Abstract

The AASHTO M332 specification includes a relationship between the non-recoverable creep compliance at 3.2 kPa (J_nr3.2) and the percent of elastic recovery (R_3.2) from the multiple stress creep and recovery (MSCR) test. Justification for the exact position of this curve based on binder performance is largely undocumented in the technical literature as is the singular effect of higher or lower R_3.2 values on mixture performance. In this study, nine binders were tested to evaluate the effect of R_3.2 on the performance of asphalt mixtures. Binders with similar J_nr3.2 and varying MSCR R_3.2 were divided into four groups based on their J_nr3.2 value. Comparisons were made based on results obtained from the dynamic modulus test, Hamburg wheel tracking test, and axial fatigue test. Based on these tests, it was shown that R_3.2 had a strong relationship to the dynamic modulus of asphalt mixtures especially at intermediate and high temperatures. Binders with lower R_3.2 had a higher dynamic modulus but showed no correlation to phase angle. Both modulus and phase angle of the mixture correlated to the binder shear modulus and phase angle. Binders with high R_3.2 had a greater fatigue resistance and the effect is quite noticeable. However, R_3.2 was shown to have little to no effect on the rutting resistance of the asphalt mixtures for the temperatures tested in this study. Finally, an alternative J_nr3.2 versus R_3.2 relationship based on the results of this study is also presented.