Evolution of the Thermo-rheological Indices of Asphalt Binders with Aging

Abstract

Reliable characterization of asphalt binder properties with aging, as a function of pavement service life, is crucial to improving asphalt binder specifications as well as modification and formulation methods. The objective of this study is to evaluate how the thermo-rheological indices of asphalt binders change over time, and explore their potential correlations. Binders from five different mixtures are subjected to various conditioning protocols (20 h PAV on original binder as well as short-term, 5 and 12 days aging at 95 °C on loose mixtures). Binder testing is conducted using a dynamic shear rheometer (DSR) with 4 mm parallel plate geometry over a wide range of frequencies and temperatures. Numerous thermo-rheological parameters are calculated to evaluate changes with aging. The results of this study indicate that the softer binders (as described by lower performance grade high and low temperatures) and the binders with the largest difference between high and low temperature performance grades show higher aging susceptibility. However, the softer binders and those extracted from virgin mixtures (without recycled asphalt) retain better cracking performance after aging. Results also indicate that binder transition temperatures (glassy transition temperature (T_g), viscoelastic transition temperature (T_t) and magnitude of the intermediate region temperature range (ΔT_IR)) generally show moderate to strong correlations with binder rheological indices (e.g. binder R-value and Glover-Rowe parameter). Binders with ΔT_IR greater than 60 °C should be avoided because of poor relaxation and cracking resistance performance. The observations from this study provide insights on the relationships between an asphalt binder’s fundamental thermo-rheological properties.