Significance of Oxidative Aging on the Thermal Cracking Predictions in Asphalt Concrete Pavements

Abstract

The resistance of asphalt concrete pavements to thermal cracking is fundamentally related to the asphalt mix stiffness, strength, and contraction properties. These properties continuously change over time with the oxidative aging of the asphalt binder in the mix. Oxidation reaction in long-term mainly results in formation of carbonyl functional group that improves the association among polar components, increasing the asphalt binder stiffness and brittleness. Hence, thermal cracking is generally more prevalent in old pavements. In this paper, a methodology is proposed to refine the mechanistic model for prediction of thermal cracking events over pavement service life in order to account for continuous changes of asphalt mixture critical properties with oxidative aging. Particularly, the changes in asphalt mix relaxation modulus, crack initiation stress, and coefficient of thermal contraction (CTC) were related to the growth in carbonyl groups in the respective binder used in the mix. The approach was examined on few types of asphalt mixes having different air void levels, and with unmodified and polymer-modified binders to be used as a surface course in a specific asphalt pavement. Based on preliminary modeling results, significant differences in thermal cracking performances of mixes were observed when effect of aging was considered.