Impact of Water on Asphalt Aging

Abstract

Atmospheric pressure aging experiments were conducted to determine whether the presence of moisture during aging at a pavement service temperature of 60°C had any significant influence on the aging kinetics of thin (100-micron) asphalt binders. The five binders studied were aged in both dry and humid atmospheres. Infrared spectra of the dry- and moist-aged binders were compared. Master curves (dry aged and moist aged) generated from dynamic shear rheometry tests were also compared. The results showed that moisture had no significant effect on the oxidation rate at atmospheric pressure. A first-order and zero-order aging kinetic model was applied to fit all the chemical results. The Arrhenius equation was employed to calculate the activation energy for carbonyl and sulfoxide formations on all of the asphalts. The observed activation energies indicated that asphalt AAD-1 was more sensitive to the aging temperatures than the other four tested asphalts on the rapid carbonyl formation. However, after the initial spurt, the reaction rate of asphalt AAD-1 became more stable than in the other four asphalts. Sulfoxide formation was also evaluated. Rheological property changes with aging correlated reasonably well with carbonyl and sulfoxide concentration changes of asphalt binders as a consequence of atmospheric pressure aging. The master curves of complex modulus and phase angle for dry-aged and moist-aged asphalt binders fall right on top of each other and indicate that aging in the presence of water (99% of relative humidity) at the ambient pressure at pavement service temperature does not influence the rheological properties of asphalt binders.