Use of polymer-modified binder has become much more important in recent years to enhance the durability and strength of asphalt concrete (AC) pavements in order to sustain higher traffic volumes, heavier loads, and extreme weather conditions. Unlike neat (unmodified) asphalt binders, polymer-modified binders are sensitive to the applied stress levels and show a nonlinear response in rutting factor and phase angle. The widely used dynamic shear rheometer (DSR) test (AASHTO T315) is not sufficient to capture viscoelastic properties of polymer modified-asphalt binders. Thus, state transportation agencies often need to conduct additional expensive and time consuming “PG Plus” tests (e.g., elastic recovery (ER), force ductility, toughness, and tenacity) for characterizing polymer-modified binders. Multiple stress creep recovery (MSCR), a recently introduced test method (AASHTO TP 70) for measuring high temperature properties of an asphalt binder, is expected to replace the existing AASHTO T315 for short-term aged binder. In the current study, MSCR and Superpave tests were conducted on three commonly used performance grade (PG) binders (PG 64-22, PG 70-28, and PG 76-28) from 12 different sources throughout Oklahoma. Based on expected traffic loads and service temperatures, the tested binder samples were graded in accordance with the MSCR grading system. The non-recoverable creep compliance (J_nr) and MSCR % recovery values obtained from the MSCR tests were then analyzed using the polymer curve and quadrant methods to assess the feasibility of the adoption of the MSCR test method for conditions prevailing in Oklahoma. Findings of this study reveal that the MSCR test method can be used to characterize polymer-modified binders without penalizing suppliers or risking the users.

This paper presents the results of a study that was conducted to understand the impacts of aging and rejuvenation on fundamental properties of asphalt binders. A Performance Grade (PG) 64-22 binder was aged to simulate the aging of asphalt mixes during construction and in-service conditions. The binders’ surface tension property, i.e., contact angles between binder and three probe liquids, was measured using a sessile drop device. This property was then used to estimate surface free energy components of the control binder, aged binders, and rejuvenated binders using the Good–van Oss–Chaudhury postulation. Cohesive and adhesive bond energies of asphalt–aggregate systems under dry and wet conditions were also analyzed. The aggregates considered in this study were limestone and granite; these aggregates have different moisture affinities. The data showed that as asphalt ages, the contact angle between a liquid (distilled water) and the asphalt surface increases; however, for the other two probe liquids (formamide and glycerol), no pattern was observed. For the surface free energy components of the control binder, the aged binders, and the binders with rejuvenators, the contribution from Lifshitz–van der Waals components were comparatively much higher than those from acidic and basic components. The rejuvenators seemed to be effective at improving the cohesive energy of asphalt binder, suggesting an improvement in the water damage resistance of the mix. In general, the limestone-based asphalt concrete mixture showed a higher moisture damage resistance than the asphalt concrete mixture with granite.