Crack Evolution of Asphalt Mixtures Under Compressive Monotonic and Repeated Loads

Field observations and mechanical analyses have shown that cracks accompany rutting in asphalt mixtures under external compressive loads. This study aims to model crack growth in asphalt mixtures under compressive monotonic and repeated loads. With hypothesizing energy equilibrium and viscoelastic Griffith fracture criterion, a damage density characterizing the cracking in a mixture is derived as a function of stress, nonlinear viscofracture strain, asphalt film thickness and bond energy. Crack evolution is modelled by pseudo J-integral Paris' law. Six types of asphalt mixture were tested by monotonic compressive strength tests at 40 degrees C. Two were further tested at 5 temperatures and 5 loading rates, respectively. Repeated load test results for the same mixtures were obtained in previous studies. It is found that the damage density shows an S-shape curve under a strain-rate controlled monotonic load and an exponential curve under a stress controlled repeated load. Pseudo J-integral Paris' law can capture the overstress softening behavior and model the crack growth in mixtures under a monotonic load. The Paris' law coefficients (A and n) are independent of loading mode (monotonic or repeated), rate or temperature. Thus they are fundamental material properties and can be used to predict crack growth under varying loading and temperature conditions.