Changes in Corbett Fraction Composition During Oxidation of Asphalt Fractions

Abstract

The naphthene aromatic (NA) fractions and polar aromatic (PA) fractions of five Strategic Highway Research Program asphalts (AAA-1, AAD-1, AAF-1, AAG-1, and AAM-1) along with six supercritical fractions of AAF-1 were subjected to oxidative aging. Asphaltenes and residual polar aromatics were recovered from the aged PA material. Produced asphaltenes and PAs and residual NAs were recovered from the aged NA samples. It was determined that NAs convert to PAs and subsequently become asphaltenes during oxidative aging of asphalt binders. However, within the extent of aging encountered in roadways, it is concluded that negligible asphaltenes are produced from NAs. Depending on the relative rates of oxidation of PAs and NAs, the content of PAs may either increase or decrease. Newly produced asphaltenes and PAs are smaller in molecular size than those present in the original whole asphalts. Also, the residual PAs in the aged PA fractions and the residual NAs in the aged NA fractions have smaller molecular size than those of the parent asphalts. The smaller molecular-sized material, whether PA or NA, is more slowly converted to asphaltenes or PAs, respectively. These data indicate that materials high in NAs and perhaps smaller PAs will harden very slowly in service.