Monitoring the Evolution of SARA Fractions During Asphalt Binder Aging by Automated HPLC and Correlation with FTIR Oxidation Indices

The qualitative evolution of SARA fractions during asphalt binder aging is well established, but further validation is needed to demonstrate whether automated HPLC-SARA analysis can provide repeatable compositional indicators for systematic aging studies. In this work, the applicability of a previously optimized automated high-performance liquid chromatography (HPLC) workflow for saturate, aromatic, resin, and asphaltene (SARA) fractionation was evaluated for the monitoring of thermo-oxidative aging. Four penetration-grade asphalt binders were subjected to short-term aging and multiple long-term aging cycles, and the resulting SARA distributions were used to calculate the colloidal instability index (Ic). Fourier-transform infrared spectroscopy (FTIR) was used as an independent reference technique to evaluate carbonyl and sulfoxide oxidation indices. The automated HPLC-SARA method provided repeatable compositional indicators across all asphalt binders and aging conditions. As expected, aromatics progressively decreased whereas asphaltenes increased, while saturates showed only limited variations and resins behaved as an intermediate operational fraction. More importantly, Ic increased consistently with aging and showed a strong correlation with the FTIR carbonyl index (R2 = 0.84 when all asphalt binders and aging conditions were considered), whereas the sulfoxide index showed a more asphalt binder-dependent response. These results demonstrate that automated HPLC-SARA analysis can provide aging-sensitive compositional and colloidal indicators that are chemically consistent with independent FTIR oxidation markers. The proposed workflow represents a complementary tool for asphalt binder aging research and may support future studies aimed at linking compositional evolution with rheological and durability-related properties.