Use of the MSCR test to characterize the asphalt binder properties relative to HMA rutting performance - A laboratory study

Permanent deformation (or rutting) is one of the common distresses occurring in hot-mix asphalt (HMA) pavements. HMA is predominantly composed of aggregates and asphalt binder; and the asphalt binder plays a significant role in the HMA performance including permanent deformation and rutting resistance. In order to characterize the properties of the asphalt binder related to HMA rutting, the Superpave performance grade system uses the high-temperature grade, which is determined based on the complex shear modulus (|G∗|) and phase angle (δ) parameter (G∗/sinδ) that is measured from the Dynamic Shear Rheometer (DSR) test. However, G∗/sinδ is not a performance-based parameter. Therefore, the Federal Highway Administration (FHWA) has developed a performance-based PG binder test, the Multiple Stress Creep and Recovery (MSCR) test, to supplement the conventional DSR high temperature test. The primary objective of this laboratory study was to compare the two asphalt binder tests (the MSCR and the DSR high-temperature grade) and two HMA rutting related performance tests (the Hamburg Wheel Tracking Test [HWTT] and the Repeated Loading Permanent Deformation [RLPD] Test) for characterizing the asphalt binder high temperature properties relative to HMA permanent deformation and rutting performance. For the asphalt binders and HMA evaluated, the MSCR showed a better correlation with the two rutting related performance tests (HWTT and RLPD) than the DSR high temperature grade. Thus, the MSCR test results shows promise to supplement or serve as a surrogate to the existing DSR test in characterizing the asphalt binder high temperature properties that are related to HMA rutting. However, more lab testing and field validation is still warranted to complement the results and findings reported herein.