Significance of Mixture Parameters on Binder Aging in Hot-Mix Asphalt Mixtures

Traditionally, aging studies of asphalt materials have been conducted primarily on asphalt binders only and have omitted any potential influence of the aggregate. These results are commonly extrapolated to the mixture behavior without a comprehensive understanding of how the mixture characteristics may potentially influence the aging of the binder within the mixture. This study was initiated by FHWA to evaluate the effects of mixture parameters—namely, different aggregate and asphalt binder sources, air voids, and binder contents—on the aging characteristics of asphalt binders aged in mixtures. Those same binders were also aged in pressure aging vessel (PAV) pans in laboratory ovens to determine the aging characteristics of the asphalt binders, as is the current state of practice. These characteristics were determined by the binder kinetics, with respect to the carbonyl area measured from the Fourier transform infrared spectroscopy spectra as a function of aging time and temperature. The hardening susceptibility (HS) of the asphalt binders, as defined by the relationship between the low shear viscosity and the carbonyl area, was also determined. The HS of the asphalt binders aged in the mixtures was compared with the HS of the binders aged in the PAV pans and was found to be statistically dissimilar for some mixtures and statistically similar for others. The analysis revealed that the effective binder content of the mixtures provided the strongest indicator of whether the evaluated mixture parameters would have a significant influence on the aging characteristics of the asphalt binder in the mix.