Coefficient of Thermal Expansion and Thermally Induced Internal Cracking of Asphalt Mixes

The coefficient of thermal expansion/contraction (CTE) is an important factor influencing the low-temperature thermal cracking of asphalt pavements. The current CTE model used for thermal cracking evaluation does not provide temperature-varying CTE values and hence, may result in inaccurate CTE values for thermal cracking prediction. Furthermore, it fails to account for transition temperature, an important parameter for low-temperature performance evaluation. Because of the significance of CTE in thermal cracking evaluation, there is the need for a comprehensive study that evaluates a robust CTE model for thermal cracking evaluation in asphalt pavements. Furthermore, the model should be able to provide temperature-varying CTE values and the transition temperature. The objectives of this study were to evaluate the parameters influencing asphalt mixture CTE, evaluate the effect of mixture CTE on low-temperature performance, and investigate the transition behavior of the mixture CTE at low temperatures. Two limestone aggregates and four asphalt binder types with different CTE values were used to prepare eight asphalt mixture combinations. Rheological properties of the asphalt binders were evaluated utilizing the bending beam rheometer. The mixture CTE values were determined using a custom-made CTE device referred to as the Ohio CTE device. The cracking temperature of asphalt mixtures was evaluated using the asphalt concrete cracking device (ACCD), a concentric thermal stress restrained specimen device. Based on the test results, it was concluded that the measured asphalt mixture CTE values were significantly lower than the values predicted by the current AASHTOWare CTE model. The cracking temperature measured by ACCD became colder as the mixture CTE became relatively lower. The transition of the mixture CTE appeared to be caused by internal cracking and could be modeled with the isochronal stiffness of asphalt binder. The mixture CTE transition temperature was highly correlated with the ACCD cracking temperature.