Evaluation of laboratort-measured crack growth rate for asphalt mixtures

A clear understanding of the cracking mechanisms of asphalt mixtures is needed to identify the most rational approach to analyzing its cracking behavior. Asphalt mixture properties were determined for eight asphalt mixtures of known cracking performance. Crack growth rates were measured in the laboratory for each mixture using the method developed by Roque et al. The crack growth rates were evaluated to determine (a) the validity of the test results, (b) the relationship if any between laboratory crack growth rates and field performance, (c) the relationship between the measured crack growth rates and other mixture properties, and (d) the validity of Paris law of crack propagation for evaluating asphalt mixture performance in the field. Through this evaluation, it was found that Paris law does not appear to incorporate all aspects involved in the mechanism of cracking of asphalt mixtures subjected to generalized loading conditions, such as those encountered in pavements in the field. Therefore, a concept appears to be warranted involving the use of fracture energy as a failure criterion for the initiation and propagation of cracks. This concept may explain both laboratory-measured crack growth rates and field cracking performance.