Effect of cooling rate on the thermo-volumetric, thermo-viscoelastic, and fracture properties of asphalt mixtures

Thermal cracking of asphalt pavements has been known to be highly influenced by both the climatic conditions at the project location and the asphalt mixture properties. Hence, characterization of asphalt mixtures under thermal regimes is essential for appropriate selection of thermal crack resistant material. In this study thermo-volumetric, thermo-viscoelastic, and fracture properties of asphalt mixtures were evaluated by measurements of thermally induced stresses and strains under various cooling rates (2.5, 5, 10, and 17.5 degrees C/hr). Dense-graded asphalt mixtures with two types of asphalt binders (unmodified and polymer-modified) were examined. Thermo-volumetric (i.e., coefficient of thermal contraction) and fracture properties were obtained directly from the thermal strain and thermal stress measurements, respectively. The thermo-viscoelastic properties at the viscous softening stage, viscous-glassy transition stage, glassy hardening stage, and crack initiation stage of the evaluated asphalt mixtures were determined from the evolution of the stiffness, i.e., modulus, as a function of temperature. The modulus was determined using the Boltzmann's superposition principle with the concurrent measurements of thermally induced stress and strain. The results showed that the fracture stress, fracture temperature, and thermo-viscoelastic properties of the evaluated mixtures were influenced by the applied cooling rate and the impact of cooling rate depended on the type of asphalt binder. The coefficient of thermal contraction was not significantly affected by the rate of cooling.