Development of a rate-dependent cumulative work and instantaneous power-based asphalt cracking performance index

Use of the semi-circular bending (SCB) test has gained popularity for evaluating cracking performance of asphalt mixtures. An Illinois Flexibility Index Test (I-FIT) variant of SCB has shown the ability to distinguish mixtures through use of the flexibility index (FI) parameter. While this index has been able to rank the mixtures with respect to performance, a high coefficient of variation (COV) among the replicates has often been observed. Furthermore, parameters such as total fracture energy and FI do not incorporate rate dependency of fracture processes which are very important for viscoelastic materials such as asphalt mixtures at low and intermediate temperatures. In light of these observations, a rate-dependent cracking index (RDCI) is proposed that utilises cumulative fracture work potential and instantaneous power calculated from the I-FIT test to assess impulse of the mixture. Thus, in spirit, this parameter captures the fracture energy and crack velocity of the material; however, these are calculated in a rate-dependent manner. A total of 18 surface course mixtures were analysed using the RDCI and resulted in an average overall reduction of 10.6% in COV as compared to FI while maintaining similar ranking of mixtures. In general, RDCI was able to better discriminate the 18 mixtures as compared to FI. The evaluation of five mixtures at three aging levels showed the robustness of RDCI in capturing effects of aging on fracture behaviour of asphalt mixtures.