Development of a modified Superpave Thermal Cracking Model for asphalt concrete mixtures based on the fracture energy approach

Thermal cracking is a serious type of pavement distress and its prevention is a critical issue for many transportation agencies around the world. The indirect tensile (IDT) creep and strength tests were developed during the Strategic Highway Research Program (SHRP) to evaluate the resistance of Hot Mix Asphalt concrete (HMA) to lowtemperature cracking. Currently, the IDT creep and strength tests are considered two of the most promising tests for predicting the low-temperature performance of asphalt concrete mixtures. The IDT tests are used as the material characterization tests for thermal fracture in the Mechanistic-Empirical Pavement Design Guide (MEPDG) of New and rehabilitated Pavement Structures developed during the National Cooperative Highway Research Program Project 1-37A.; The existing Thermal Cracking Model (TCMODEL) that is currently an integral part of the MEPDG has proved to adequately predict low temperature cracking of asphalt concrete mixtures utilizing conventional binders that have distinct (or extreme) characteristics. Thermal fracture characterization evaluation studies conducted in this research concluded that the IDT procedures need certain refinements and revisions. In addition, test results from several asphalt rubber mixtures in this research have shown that the existing TCMODEL in the MEPDG falls short in properly predicting the observed thermal cracking resistance of these mixtures in the field.; A major accomplishment of this research was the development of a new method for evaluation of the thermal cracking potential in HMA, with focus on mixtures with modified binders like asphalt rubber mixtures. Necessary revisions and refinements of the existing IDT test protocol were made, and an IDT test results database was created and used in the development of a new Crack Depth Fracture Model that was based on utilizing fracture energy. In addition, a set of predictive equations were developed for the use in MEPDG level 3 thermal cracking analyses. This work included the revision of the existing predictive equations for the creep compliance and tensile strength parameters, as well as, development of a new equation to predict the total fracture energy. These prediction equations are based on correlations of the laboratory measured parameters with binder and mixture properties.