Evaluation of ageing behaviors of asphalt binders using FTIR tests

The main objective of this study was to evaluate ageing behaviors of matrix and modified asphalt binders using different Fourier transform infrared (FTIR) spectral indices, based on FTIR tests. These FTIR indices include normalized carbonyl (C=O) absorption peak area (A1700), normalized sulfoxide (S=O) absorption peak area (A1030), carbonyl index (CI) and sulfoxide index (SI) based on five different reference groups. The rolling thin film oven test (RTFOT) was applied to simulate thermal oxidation ageing. Then, physical properties tests (softening point, penetration, ductility, and viscosity) and FTIR tests were conducted on the studied asphalt binders (AH-50, AH-70, AH-90 matrix asphalt, and SBS-70 modified asphalt) with different ageing states. Meanwhile, ageing behaviors and their relationship characterized by the physical parameters and FTIR indices were studied and discussed. The results show that the changes with ageing time of FTIR indices and physical parameters are in accordance with ageing kinetics law, and normalized A1700, CI can interpret the ageing behavior as well as physical parameters. Normalized A1700 is easier to obtain and recommended as the optimal ageing evaluation index among FTIR indices. The evaluation results of asphalt anti-ageing ability by selected FTIR indices are consistent, and SBS-70 modified asphalt exhibits the best ageing resistance among all tested technical parameters.