Optimization of Fracture and Moisture Damage Resistance of Stone Matrix Asphalt Mixtures Containing Crumb Rubber-Modified Binder with the Fracture Mechanics Approach

The use of crumb rubber-modified binder (CRMB) as a binder in stone matrix asphalt (SMA) mixture design, in addition to the environmental approach, has shown several positive points in the technical performance of these types of mixtures. The important issue in the mixture design of SMA containing CRMB is the most optimal performance conditions, especially the fracture properties based on the variables of the mixture design, including the CRMB content and the number of gyrations required for compaction ($N_{\mathrm{design}}$). For this purpose, in this study, the mixture design of SMA containing CRMB was carried out through the optimization of moisture susceptibility and cracking resistance at low and intermediate temperatures with the approach of fracture mechanics. After performing required tests in different plans resulting from the design variables and analyzing the results, the optimization process was carried out based on the regression models obtained from the test data. The results showed that in SMA mixtures containing CRMB, the $N_{\mathrm{design}}$ is the dominant factor in cracking resistance. Also, the optimization of the mixture design of SMA containing CRMB based on cracking criteria such as moisture susceptibility, and cracking resistance at low and intermediate temperatures showed that 7.5% of CRMB with $N_{\mathrm{design}}=87$ provides an optimal mixture design to maximize the fracture criteria by satisfying the volume criteria; it meets current guidelines and with the desirability of 0.621.