Investigation into the Oxidative Aging of Asphalt Binders

Abstract

Oxidative aging is caused by oxygen diffusion into the binder when an asphalt pavement is exposed to the atmosphere. Aging can lead to increased susceptibility to pavement damage (i.e., raveling, cracking, and moisture damage). Investigation of the aging mechanism advances the understanding of these pavement distresses, and prediction of the aging progress improves structural design and prediction of pavement performance. Previous studies have proposed a dual-rate aging model that divides the aging progress into a short, fast-rate phase and a long constant phase. This paper further investigates the constant rate aging phase of unmodified, polymer modified, and asphalt rubber binders. The chemical composition (carbonyl, sulfoxide, ether, and ester) and the rheological properties (shear modulus and viscosity) changes were tracked to analyze the binder aging mechanism. As expected, the carbonyl component was found to consistently increase with aging time. The widely used aging model with kinetics parameters estimated from the accelerated laboratory test predicted the field-aging progress reasonably well. A linear correlation between the logarithm of viscosity change and the carbonyl change was found to be valid for a wide range of loading temperatures and frequencies. Furthermore, the slope of this linear correlation was found to be in perfect linear correlation with the loading frequency. These findings point to a generic framework for studying aging and its effect on asphalt binders, as well as asphalt concrete mixes.