Analysis of MSCR test results for asphalt binders with improved accuracy

The multiple stress creep recovery (MSCR) test has been regarded by many as the best available test method to evaluate the high-temperature performance of asphalt binders. However, recent studies have shown that the 9-s recovery time may not allow a full recovery of viscoelastic strain for some modified asphalt binders. In that case, some potential viscoelastic recovery is mistakenly reported as unrecovered strain, leading to an underestimation of the asphalt binder rutting resistance. In order to address the issue of incomplete recovery, this paper developed a mechanistic modeling approach to analyze the MSCR test results of six types of asphalt binders. Before using the mechanistic modeling approach, the steady-state strain response at each stress level was firstly determined for all asphalt binders. It was found that the three neat asphalt binders reached a steady-state condition from the beginning of the last 10 cycles, whereas the SBS-modified asphalt binders reached a relatively steady state in the last 5 cycles. Afterwards, a mechanistic modeling approach was employed to analyze the shear strain data in the last 5 cycles at each stress level based on the Boltzmann superposition principle and the Schapery’s nonlinear viscoelastic theory. The viscoplastic strain at the end of the recovery portion and the viscoelastic strain at the end of the creep portion were utilized to calculate the non-recoverable creep compliance and percent recovery. It was demonstrated that the approach adopted in this study was capable of analyzing the MSCR test results of asphalt binders with improved accuracy.