Effect of Different Loading Conditions on the Fatigue Response and Recovery of Neat and Modified Asphalt Binders

Abstract

Abstract Thixotropic behavior is a reversible process that occurs in asphalt binders because of the breakage and restoration of the binder’s microstructure. Thixotropic effects are associated with load applications and are fully recoverable when the loading is discontinued. Fatigue loading results in a decrease in the asphalt binder’s modulus related to reversible phenomena such as thixotropy, healing, and self-heating, in addition to irreversible permanent fatigue damage. The study of thixotropy is important to better characterize damage because of fatigue. In this study, four different asphalt binders were tested to determine their thixotropic behavior, namely two neat PG64-16 binders from different refineries, a polymer modified PG64-28 binder, and a tire rubber modified PG64-28 binder. The binders were short-term aged using a rolling thin film oven and tested with a dynamic shear rheometer at temperatures that produced an initial modulus of 35 MPa at sinusoidal strain amplitudes of 1.2 and 1.4 %, and an initial modulus of 50 MPa at strain amplitudes of 1 and 1.2 %. The test temperatures corresponding to the initial moduli for each binder were determined using a temperature sweep at a test frequency of 10 Hz. The test temperature and strain amplitudes were applied for 500 or 1,000 s followed by rest periods to determine the effects of loading time on the rates of binder modulus recovery for the different conditions. The results indicated that the thixotropic recovery rate is dependent on the binder type, with the tire rubber modified binder showing the fastest recovery rate and the polymer modified binder showing the slowest recovery rate. The recovery rate was also shown to increase with increasing initial modulus and strain amplitude.