Analysis and Comparison of Different Impacts of Aging and Loading Frequency on Fatigue Characterization of Asphalt Concrete

Asphaltic material is a kind of viscoelastic material, and its performance varies with test and materials conditions, such as stress states, temperatures, aging degree, gradations, and binders. The anti fatigue design of asphalt pavement has been stifled by these interferences. The objectives of this study are to reveal and compare the effects of loading frequency and aging degree on the fatigue performance of asphalt concretes. A series of tests for tensile fatigue on aged and unaged asphalt concretes were conducted at different loading frequencies. The theory of stress ratio considering different test conditions was proposed based on the conclusion that the stress ratio varies with stress loading rates. Then, the S-N fatigue equation was modified based on the theory. The fatigue test results were analyzed with the modified S-N fatigue equation to characterize the fatigue performance of asphalt concretes aged to different degrees under different loading frequencies. The different effects of these two factors on the fatigue characteristics of asphalt concretes were analyzed and compared. It could be found from the results that the influences of loading frequencies and aging degrees on fatigue characteristics of asphalt concrete were different. The fatigue test results of asphalt concrete under different loading frequencies could be characterized by one fatigue curve fitted by the modified S-N fatigue equation. It meant that the effects of loading frequency on fatigue were equivalent to the stress level. The fatigue test results of asphalt concrete with different aging degrees were fitted into different fatigue curves, respectively. The asphalt concretes aged 1 day had better fatigue life and more stable stress sensitivity than unaged asphalt concrete. When the aging degree was over 1 day, the fatigue performance deteriorated with the increase of aging degree. Moreover, it could be observed that the strength increased with the aging degrees when it was measured by the standard test loading rates. However, when the loading rates increased to a certain range, the contrary conclusion could be obtained because the viscoelasticity of asphalt concretes changed due to aging. (c) 2020 American Society of Civil Engineers.