Impact of shear stress levels on validity of MSCR tests

Although the MSCR test has become an improvement over the Superpave® |G*|/sinδ parameter, shear stress levels specified in the MSCR test might prove to be too low to successfully represent the stresses occurring in the pavement. To address this hypothesis, five conventional asphalt binders and a total of twelve polymer-modified asphalt blends were tested by MSCR at two different temperatures (50°C and 60°C) as well as five different shear stress levels of 0.1, 3.2, 6.4, 12.8, and 25.6 kPa. The rut results of hot mix asphalts were correlated with the MSCR results. Consequently, better correlations were obtained at higher shear stress levels used in performing MSCR. Moreover, it was shown that MSCR test overestimated the positive effects elasticity on the asphalts’ rut resistance and, thus, more consideration should be given to the asphalt’s ability to resist the applied stresses than to its elastic recovery.