A Composite Model for Predicting the Coefficient of Thermal Contraction for Asphalt Concrete Mixtures

Thermal cracking is one of the most prevalent types of distress found in asphalt concrete pavement sections. The coefficient of thermal contraction (CTC) is the intrinsic parameter that determines the thermal contraction of asphalt mixtures subjected to temperature drop. Thus, thermal stress and associated thermal damage are greatly affected by the CTC of the mixture. The direct measurement of a mixture’s CTC is the most reliable and at the same time cumbersome method for predicting the thermal contraction of asphaltic mixtures. In this study, for Level I analysis, we measured the CTCs of mixtures that have a wide range of properties and reported the data. In order to remedy the difficulties associated with directly measuring CTC, we herein propose a simple yet accurate composite model. The suggested approach enables pavement engineers to predict CTC values as the temperature drops. The formulation requires the mixture’s volumetric properties, elastic modulus, and CTC of the aggregate a priori. With regard to binder, the formulation requires the CTC and relaxation modulus as input parameters. This procedure constitutes the Level II analysis for which the binder CTC is required beforehand. A database that constitutes a basis for estimating binder CTC was developed from measurements reported in the literature. The database can be used to fill the value for binder CTC in the developed composite model for the sake of predicting mixture CTC. This procedure constitutes Level III analysis. Levels II and III only differ with respect to the input value for binder CTC. The CTC values from the measurements and predicted from the composite model (Levels II and III) are compared. In order to fully understand the effects of Level II and III errors in estimating mixture CTCs, we also compared the thermal stress obtained from the predicted and measured CTCs.