Experimental investigation and modeling of fatigue behavior of asphalt materials

Zhang, Zeyu; Oeser, Markus (Thesis advisor); Jelagin, Denis (Thesis advisor)

Aachen : RWTH Aachen University (2021)
Dissertation / PhD Thesis

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2021

Abstract

Asphalt materials are subjected to millions of load repetitions after opening to traffic. Although they may not be destroyed because of a single load pass, due to fatigue damage, the performance of asphalt materials will deteriorate as the number of load repetitions increases. Properly understand and model the fatigue behavior of asphalt materials have attracted much attention from pavement researchers and engineers for a long time because of the complex nature of fatigue behavior. This thesis was conducted aiming at making a contribution to this topic. This thesis started by modeling the damage evolution behavior of the asphalt mixture. Residual strength was selected to indicate the fatigue damage of the asphalt mixture considering its concrete mechanical meaning in identifying the fatigue failure point. The theoretical background of this model yielded that the fatigue damage of materials may occur on two scales, namely, macro scale and micro scale, depending on the magnitude of the applied load. In addition, the proposed damage evolution model showed the nonlinear nature of fatigue damage accumulation under repeated loads with variable amplitudes. To verify these hypotheses, a series of time sweep tests were conducted on four types of asphalt binders. The failure pattern, rheological properties, and dissipated energy were used to assess the fatigue response of the asphalt binder. The experimental results indicated the two-scale characteristics of fatigue damage and the different failure modes of the asphalt binder, revealing cracking is not the only manifestation of fatigue damage. The transition point between two failure modes and the damage scale crossing threshold were analyzed based on the residual strength of the asphalt binder and the effective shear stress. Then, a variable amplitude time sweep test method was proposed to investigate the fatigue response of the asphalt binder to compound loads consisting of two types of fatigue loads. The experimental results confirmed the nonlinear accumulation characteristics of fatigue damage, indicating the incapability of conventional Miner’s rule in accurately predicting remaining fatigue life. A nonlinear damage accumulation model, named as Oeser & Zhang (orz) model, was proposed to fill this gap. Lastly, the energy dissipation behavior of asphalt binders under two types of fatigue loads was characterized by dissipated energy and energy-based indicators. The performance of some of the energy-based failure criteria was found to be load-dependent.

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