Prediction of Low Temperature Crack Spacing in Asphalt Pavements

Resumo

The recently released AASHTO Design Guide incorporates a number of models that address the different distresses that occur in asphalt pavements. The model used for low temperature cracking (called the Thermal Cracking or TC model) is based on a modified Paris law approach that is more appropriate for thermal fatigue type of cracking. Based on an empirical statistical analysis the model uses the crack propagation evolution to predict the number of cracks and the crack spacing that can develop during the life of a given pavement. A simple model was recently developed at the University of Minnesota based on the asphalt mixture tensile strength and the balance between the temperature shrinkage and the friction at the interface between the asphalt layer and the aggregate base. The model requires both asphalt mixture properties and aggregate properties and, similar to the TC model, predicts the crack spacing for a given pavement configuration. Unlike the TC model, it does not consider any crack evolution and cracks form instantaneously when the thermal stress in the asphalt layer exceeds the asphalt mixture strength. In this paper the two models are tested against field data from Mn/ROAD cells for which crack spacing information was available and recommendations for an improved crack spacing prediction model are made.