Fatigue Analysis of Asphalt Mixtures Independent of Mode of Loading

Fatigue cracking is a common form of distress in asphalt pavements. During the last four decades, significant research has been conducted to characterize fatigue damage in asphalt mixtures. This paper evaluates an analytical method that is independent of the mode of loading (controlled strain or controlled stress) to quantify the fatigue resistance of asphalt mixtures. The evaluation was based on fatigue tests conducted on the tine aggregate matrix (FAM) portion of an asphalt mixture by using a dynamic mechanical analyzer. A number of tests were performed by applying oscillatory torque under controlled-strain and controlled-stress conditions at a frequency of 10 Hz and a temperature of 25 C. The data from these tests were analyzed by using a fracture model for viscoelastic materials to calculate a fatigue damage parameter, R(N), which represents the influence of the numbers of cracks with equivalent crack radii on the material fracture behavior and which quantifies crack growth in FAM. This damage parameter has a coefficient of variation lower than the coefficients of variation of conventional parameters, such as the number of load cycles to failure and the cumulative dissipated energy. In addition, this parameter provides comparable results for a given material independent of the mode of loading.