Modeling temperature distribution and thermal property of asphalt concrete for laboratory testing applications

Material characterization from laboratory tests on asphalt concrete or predictions of pavement performance are meaningful only if temperature of the material is well taken into account. This paper discusses an analytical model to predict the transient temperature distribution within asphalt concrete and to determine its thermal properties. The paper also presents the laboratory test program designed to validate the model. Temperature measurements were carried out on a cylindrical specimen at different times after the specimen with a steady-state low temperature (3.5 °C) was placed inside an environmental chamber in a steady-state high temperature (36 °C). The temperature magnitude at different positions and its variation with time was recorded at a sampling rate of 1 min^-1. The analytical temperature models based on the classical planar wall and long cylinder were established to approximate the temperature distribution of asphalt concrete specimens with the geometry of a short cylinder or a beam. Thermal diffusivity as a function of thermal conductivity and heat convection is solved from the models, and then back-calculation was conducted to achieve the thermal properties using curve fitting. It was found that the analytical model could predict the measured temperatures reliably. For the materials used in this research, a thermal conductivity of 2.88 W/m °C and diffusivity of 1.42 × 10^-6 m²/s were attained from the back-calculation. The time-temperature relationship, as determined from the prediction model, was found to be very sensitive to the geometric size and thermal properties of asphalt concrete.