Comparison of fatigue analysis approaches for predicting fatigue lives of hot-mix asphalt concrete (HMAC) mixtures

Hot-mix asphalt concrete (HMAC) mixture fatigue characterization constitutes a fundamental component of HMAC pavement structural design and analysis to ensure adequate field fatigue performance. HMAC is a heterogeneous complex composite material of air, binder, and aggregate that behaves in a non-linear elasto-viscoplastic manner, exhibits anisotropic behavior, ages with time, and heals during traffic loading rest periods and changing environmental conditions. Comprehensive HMAC mixture fatigue analysis approaches that take into account this complex nature of HMAC are thus needed to ensure adequate field fatigue performance. In this study, four fatigue analysis approaches; the mechanistic empirical (ME), the calibrated mechanistic with (CMSE) and without (CM) surface energy measurements, and the proposed NCHRP 1-37A 2002 Pavement Design Guide (MEPDG) were comparatively evaluated and utilized to characterize the fatigue resistance of two Texas HMAC mixtures in the laboratory, including investigating the effects of binder oxidative aging.; Although the results were comparable, the CMSE/CM approaches exhibited greater flexibility and potential to discretely account for most of the fundamental material properties (including fracture, aging, healing, visco-elasticity, and anisotropy) that affect HMAC pavement fatigue performance. Compared to the other approaches, which are mechanistic-empirically based, the CMSE/CM approaches are based on the fundamental concepts of continuum micromechanics and energy theory.; The CMSE/CM approaches utilize the visco-elastic correspondence principle, Paris' Law of fracture mechanics, and Schapery's work potential theory to monitor cumulative fracture damage in HMAC mixtures under laboratory repeated uniaxial tensile tests. Additionally, the CMSE/CM results exhibited relatively lower statistical variability.; For the materials and test conditions considered, laboratory aging reduced HMAC mixture fatigue resistance and its ability to heal. This finding signifies the importance of discretely incorporating aging effects in HMAC mixture fatigue characterization, and the CMSE/CM aging shift factors developed in this study produced promising results. In terms of HMAC mixture comparison, the results showed that HMAC mixture fatigue resistance is a complex function of mix-design parameters, material properties, traffic, pavement structure, and environment, and that these factors need to be taken into account when modeling HMAC mixture fatigue resistance. However, more research is recommended to further validate the CMSE/CM approaches and quantify the effects of aging.