Energy-based crack initiation model for load-related top-down cracking in asphalt pavement

This paper aims at investigating the mechanisms of load-related top-down cracking (TDC) and developing a framework to predict the TDC initiation life for asphalt pavements. Firstly, a three-dimensional model is constructed to simulate the pavement responses to traffic loading. The critical pavement responses (e.g., shear and tensile stresses) are identified and related to TDC initiation at different locations (i.e., longitudinal wheel path, longitudinal non-wheel path, and transverse direction). Secondly, an energy-based TDC initiation model is developed, which involves seven sub-models and one cracking initiation criterion. The cracking initiation model takes into account the effects of aging and healing on the cracking performance of asphalt mixtures. If the load-induced damage to the asphalt pavement exceeds the limited strain energy of the asphalt mixture, the crack will initiate at the pavement surface. Accordingly, this study develops the sub-models to calculate the tensile and shear stress induced damage to the asphalt pavement, and the limited strain energy of the asphalt mixture in tension and shear modes of fracture. Finally, the TDC initiation model is used to predict TDC development for six pavement sections at National Center for Asphalt Technology (NCAT) Test Track. The prediction results indicate that the load-related TDC always initiates in the longitudinal wheel path. Increased compaction density slightly prolongs the TDC initiation life of the asphalt pavement, while decreased compaction density significantly diminishes the TDC performance. The use of soft binder with more reclaimed asphalt pavement (RAP) and the use of highly polymer modified asphalt are both beneficial for the improvement of TDC performance, but the addition of reclaimed asphalt shingles (RAS) is detrimental to the resistance of asphalt pavement to TDC. The model prediction results are in good agreement with the field observations to date.