Simplified Thermal Stress Model to Predict Low Temperature Cracks in Flexible Pavement

Thermal stress due to a decrease in temperature is usually considered the product of modulus of Hot-Mix Asphalt (HMA), coefficient of thermal contraction (CTC) of HMA and the decrease in temperature. The effects of viscoelasticity, nonlinear temperature profile and stress history on the modulus of asphalt concrete were widely explored in the literature. However, the nonlinear behavior of CTC was neglected in all thermal stress models. This study incorporates the temperature-dependent CTC in a simplified thermal stress model and validates the results comparing with the field observations. As the first step, this study measures the dynamic modulus at low frequency and low temperature. The CTC of asphalt concrete is then determined in the laboratory at different temperatures and validates the results using the data from an instrumentation pavement section. Then, the thermal stress model has been developed using the low temperature CTC, temperature and frequency dependent stiffness and the decrease in temperature. Finally, these models are used to predict transverse crack spacing and are compared with two field observations. In addition, the critical temperature of asphalt concrete is predicted with age of pavement by intersecting tensile strength and developed tensile stress curves. Results show that the simplified viscoelastic model - without considering stress history and nonlinear temperature profile - predicts the crack spacing accurately. In addition, the critical temperature of asphalt concrete is not a constant value. It increases with the age of the pavement.