Fatigue Properties of Asphalt Materials at Low In-Service Temperatures

Abstract

Fatigue damage is one of the most common distresses observed in the asphalt-concrete pavements. Both the initiation and propagation of fatigue cracking are complicated and very difficult to detect because they develop generally within pavement structure. To understand the fatigue performance of asphalt concrete thoroughly, the behaviors of the major components of asphalt concrete under cyclic loading were investigated in this study. A new experimental method was developed to evaluate the performance of asphalt binder, mastic, and fine-aggregates mixture under cyclic tensile loading. The test results showed that fatigue performance of asphalt binder is closely related to the loading magnitude, temperature, and loading frequency. Mastic specimens with varied filler contents were tested. It was found that the mastic specimen with 30% filler content had better fatigue resistance and higher permanent strain. The differences between the test results of mastic and mixture were then compared and analyzed using X-ray tomography imaging. It was indicated that the fatigue resistance is closely related to the air-void content of the specimens. Three-dimensional digital specimens of asphalt binder, mastic, and mixture were developed and tested in the numerical simulation of fatigue tests based on the finite-element method. Both mastic and mixture were modeled as heterogeneous composite materials in which the asphalt binder, filler, and aggregate were described by different mechanical models. Fatigue damage of asphalt concrete was simplified by a damage model, which characterizes the degradation of the elastic modulus of the asphalt binder. It was found that with proper selection of damage parameters, the simulation results agree well with laboratory test results and can be used as a basis for future fatigue research. Finally, the reinforcement effect of basalt fiber was evaluated as an additive to improve the fatigue resistance of asphalt-binding materials. It was found that with proper content, the fatigue resistances of asphalt binder and mastic were significantly improved. The numerical simulation analysis also showed that fibers release the stress concentration in the interface area of two fillers and mitigate the fatigue damage caused by cyclic loading.