Evaluation of Chemical and Rheological Aging Indices to Track Oxidative Aging of Asphalt Mixtures

Oxidative age hardening in asphalt binder leads to embrittlement. Embrittled asphalt is prone to fatigue and thermal cracking. Therefore, the ability to predict asphalt binder oxidative age hardening within a pavement throughout its service life could inform improved pavement material selection, design, and maintenance practices. Studying the evolution of oxidative aging requires the use of key properties to track oxidation levels, termed aging index properties (AIPs) here. The objective of this study is to identify suitable rheological and chemical AIPs to track oxidation levels in asphalt materials. A wide range of laboratory and field aged materials were evaluated in this study. A range of chemical AIPs determined by Fourier transform infrared spectroscopy (FTIR) absorbance peaks and areas were evaluated based on their correlation with laboratory aging duration. Rheological AIPs were evaluated based on the strength of their relationship to the chemical changes induced by oxidation. The rheological AIPs evaluated included the dynamic shear modulus, zero shear viscosity, Glover-Rowe parameter, and crossover modulus. The chemical AIP evaluation that most strongly correlated with laboratory aging duration is the carbonyl plus the sulfoxide absorbance peaks. The results indicate that both the dynamic shear modulus and Glover-Rowe parameter constitute rheological AIPs that relate directly to the chemical changes induced by oxidation.