Evaluation of Age-Hardening on Long-Term Aged Asphalt Binders

Abstract

Oxygen reacts with asphalt binders over time. This time-dependent reaction generates aged asphalt binder that is vulnerable to diseases (i.e., fatigue cracking) in the service stage. Investigation into oxidative aging and its impact on asphalt binder property improve the evaluation of asphalt concrete performance. This paper studied the long-term oxidative aging of unmodified, styrene–butadienestyrene (SBS)- modified and rubber-modified binders. Chemical changes in the binder were tracked by carbonyl area index measured with Fourier-transform infrared reflection spectrometer. The SBS- and rubber-modified binders showed a fewer increase of carbonyl area index than unmodified binders from the same refinery after pressure aging vessel (PAV) protocol. This study also evaluated the change in the binder viscosity that was calculated from dynamic moduli and phase angles. One previous study has proposed a generic hardening susceptibility (GHS) model to describe the linear correlation between the change of logarithmic viscosity and the change of carbonyl area index. This study modified the preliminary GHS model to improve the prediction accuracy of the long-term aged binder viscosity based on the linearity principle between total logarithmic viscosity and carbonyl area index in a wide range of testing temperatures and loading frequencies (between 20 °C and 85 °C and frequencies between 0.0159 Hz and 3.99 Hz). This linearity defines a GHS parameter that can indicate the age-hardening of the binder viscosity. Comparison between model predicted viscosities and measured viscosities shows that the GHS model can predict the viscosity of PAV-aged binder at the investigated temperature and frequency using carbonyl area index and GHS parameter.