Damage and fracture characterization of asphalt concrete mixtures using the equivalent micro-crack stress approach

In this paper, a new parameter termed “equivalent micro-crack stress” (σmc) is proposed for the evaluation of the cracking performance of asphalt mixtures with respect to their resistance to the initiation of micro-crack. The “equivalent micro-crack stress” (σmc) is a function of the material stiffness and the “micro-crack initiation threshold” (MCIT). The MCIT is a critical strain energy density at the instance of initiation of micro-crack. Experimental testing is carried out for the evaluation of the cracking performance of unmodified and wax modified asphalt mixtures using the Superpave IDT tests at −20 °C, −10 °C and 0 °C. The low temperature range is used in the study to minimize the effect of viscoplastic dissipation on the material cracking behaviour. The result shows that the “equivalent micro-crack stress” (σmc) gives a good indication of the material cracking performance of the unmodified and wax modified mixtures. A Finite Element Analysis is performed to assess the validity of the proposed approach under cyclic loading condition in the controlled-stress mode. The result shows that there is a good agreement between the material cracking performance in both monotonic and cyclic loading conditions using the proposed approach. The higher the “effective micro-crack stress” (σmc) , the better the fracture performance of the mixture.