Field aging effect on chemistry and rheology of asphalt binders and rheological predictions for field aging

Abstract

This work aims to investigate the field aging effect on binder rheology and structure and to establish the structure–rheological property relationships with the ultimate goal of predicting rheology of field aged binders. Three unmodified binders from different crude oil sources after varying field aging severities were examined in this work. The binders were extracted and recovered from pavement cores at varying depths from two field sites in Arizona and Virginia. The observed rheological hardening is closely correlated and attributed to the compositional changes within asphalts upon field aging, which involves the conversion of aromatics into toluene soluble asphaltenes and an increase in total pericondensed aromaticity and carbonyl and sulfoxide functional groups. Although the rheology is significantly impacted by field aging, the temperature dependence of rheological properties maintains unchanged at various aging severities. The Arrhenius temperature dependence is suggested to describe the viscoelasticity of unmodified binders rather than the Super-Arrhenius or Vogel–Fulcher–Tamman or Williams–Landell–Ferry equations due to a small dynamic fragility of 16. Both the rheological and chemical composition results suggest that the bottom slice (∼75mm from pavement surface) of the 8-year old ambient field aged core has similar aging severity to the rolling thin film oven (RTFO) followed by pressure aging vessel (PAV) aging on the control binder. This implies that the field aging on the pavement surface is far more severe than the long term laboratory RTFO PAV aging. Based on the observed structure–rheology relationships and Christensen–Anderson (CA) model, the rheological responses can be successfully predicted for field aged binders at various aging severities or at different pavement depths. The predictions are in good agreement with experimental results.