Wide thermal cracks are a common form of pavement distress affecting primary state and county highways, urban residential streets, and parking lots across the Southwest climatic regions. These cracks are primarily caused by thermal fatigue, driven by diurnal temperature variations despite the lack of extremely cold events. This research aims to identify and analyze the local factors contributing to the initiation and propagation of thermal fatigue cracks. Field cores are collected from 12 sites exhibiting wide thermal cracks in the Phoenix metropolitan area in Arizona to evaluate their volumetric properties and the degree of binder aging. Advanced finite element (FE) models were developed to examine the influence of pavement structures and local climatic conditions on the development of tensile stresses due to thermal fatigue. The FE analysis indicated a high magnitude of thermal stresses due to cyclic temperature variations in Arizona compared to colder regions in the United States. Based on the forensic investigation and analysis performed, the initiation of wide cracks was shown to be primarily due to repeated localized damage from frequent thermal fatigue events on severely aged pavements. This damage is exacerbated by low air voids in mineral aggregate, an insufficient effective binder volume. and excessive binder aging, which compromise the structural integrity of the pavement.

An accelerated laboratory mixture long-term aging (LTA) protocol is developed for applications in extreme climatic conditions. The Phoenix metropolitan area in Arizona, U.S.A., is selected as the region of interest because of its extended exposure to high summer temperatures. The National Cooperative Highway Research Program (NCHRP) 09-54 project recommended a climatic aging index model that predicts the oven aging period to simulate various degrees of field aging at different pavement depths. The laboratory conditioning is determined to be 17 days of loose mixture aging at 95°C. Five different binder types are selected for the development and verification of the accelerated LTA protocol. An accelerated oven aging temperature of 135°C is selected. The equivalent aging period is estimated using the NCHRP 09-54 project kinetic model. Considering practicality, a 30-h oven aging period is selected for the proposed LTA protocol. The applicability of this protocol is investigated using rheological, chemical, and mixture-level fracture experiments. A multitude of parameters are used to compare the proposed LTA protocol with the NCHRP-recommended protocol. The results demonstrate that both LTA conditions are consistent across all tests performed. For modified binders, the two aging conditions produced nearly identical results. However, some discrepancies are observed, particularly in the rheological parameters of the unmodified binders, verifying the additional aging hours predicted by the kinetics oxidation model. The consistency of the results between the two aging temperatures at the mixture level verifies the feasibility of using 135°C as part of a LTA protocol in the balanced mix design applications.