Separation of Thixotropy from Fatigue Process of Asphalt Binder

The fatigue performance of asphalt binder is critical to understanding the fatigue performance of asphalt mixtures. For the fatigue process to be modeled properly, the mechanism responsible for the fatigue behavior must be understood properly. In asphalt binder, it is widely accepted that the fatigue process is related to damage. However, some researchers have used the concept of thixotropy to describe the fatigue process in binder with equal success. If the real mechanism responsible for the observed reduction in modulus during a fatigue test is not properly understood, misinterpretation may occur. Such misinterpretation may lead to an improper assessment of a given material's quality and the acceptance of bad or rejection of good materials. This study attempted to separate the influence of thixotropy from other mechanisms during a fatigue experiment Tests were performed to characterize the exponential thixotropy model of four typical asphalt binders. The relationships between dynamic modulus and phase angle in a fatigue test and in a healing test were compared to determine the thixotropy-influence phase. According to the thixotropy model and fatigue test results, thixotropy is separated from the damage process for the entire fatigue test. A value of 50% |G*| after separation is put forward to evaluate the true fatigue characteristics of asphalt binder. The findings from this study, although based on a limited number of binders, suggest that thixotropy plays an important role in the fatigue characteristics of asphalt binder. The findings also provide a reasonable failure criterion for defining a fatigue evaluation index.