Development of a new cracking index for asphalt mixtures using indirect tensile creep and strength test

Abstract This paper aimed at developing a new cracking index (CI) for asphalt mixtures using the indirect tensile creep and strength test (IDT-CST). Firstly, the effectiveness of existing cracking parameter of IDT-CST (i.e., energy ratio) was evaluated by comparing the laboratory energy ratio results to the field cracking performance. It was found that the energy ratio parameter could not properly demonstrate the aging effect on cracking resistance. Besides, the energy ratio results had a poor correlation with the field cracking performance. Secondly, this study collected 87 IDT-CST datasets and evaluated the interrelations among the test parameters, such as fracture energy, limited dissipated creep strain energy, failure strain, resilient modulus (MR) and secant modulus (MS). The test results indicated that the fracture energy was well correlated with the limited dissipated creep strain energy and failure strain. This suggested that the limited dissipated creep strain energy be simply replaced by the fracture energy to characterize the cracking potential of asphalt mixture. In addition, there was a good relationship between MS and MR. Thirdly, two new CIs were developed to quantify the cracking potential of asphalt mixtures, which were dependent on the fracture energy and secant modulus (or resilient modulus). The field cracking performance data from the four existing projects were collected to determine the CI coefficients. Compared to the energy ratio parameter, both new CIs showed more reasonable indication of aging effect on cracking potential, and manifested better correlations with field cracking performance. Finally, the effectiveness of new CIs were validated by using an independent group of laboratory and field cracking data. Both the MS-based CI and the MR-based CI had satisfied correlations to the field cracking performance with the R2 values equal to 0.72 and 0.90, respectively. Considering the test efficiency and equipment cost, the MS-based CI was superior to the MR-based CI in the evaluation of cracking resistance of asphalt mixtures.