Effect of Cooling Rate on Thermal Cracking of Asphalt Concrete Pavements

Low temperature binder property specification as thermal cracking prevention criteria is something that asphalt concrete material selection procedures mainly rely on. In these methods, however, there is not rigorous consideration of the effects of cooling rates. Cooling rate effects on thermal stress accumulation in asphalt pavement are examined in this study. There have been indications through enhanced integrated climatic model simulations that the high cooling rate and lowest pavement temperature events usually do not occur simultaneously. There are frequent high cooling rate event occurrences in the 1 to 3 degrees C/hour range in more severe climates, including the American midwest. There can be relatively easy estimation of thermally induced stresses using Boltzmann's superposition principle and fundamental viscoelasticity formulations. Relaxation modulus, creep compliance, and other low temperature viscoelastic properties can be utilized by this formulation as an input and can be readily used as a tool for identifying materials with high thermal cracking susceptibility resulting from severe cooling rate. For asphalt concrete's thermal cracking performance dependence on cooling rates verification, the author studied five SHRP General Pavement Study section mixtures. There was computation, at different rates, of thermally induced stress for a pavement section through viscoelastic finite-element simulations. Additionally, the AASHTO Mechanistic Empirical Pavement Design Guide's thermal cracking software, TCMODEL, was used to make thermal cracking predictions. Significant variation in induced thermal stress amount was found for different cooling rates for asphalt concrete mixtures produced with the same Superpave binder grades. Poor field performance was found and poor finite-element and TCMODEL simulation performance was predicted for mixtures with high stress accumulations according to the analytical solution. Study results indicate that there needs to be consideration of both cooling rate and lowest pavement temperature in low temperature cracking performance evaluation.