FTIR analysis of UV aging on bitumen and its fractions

The ultraviolet (UV) aging of bitumen involves a series of complex chemical reactions due to its complicated chemistry and structure. To conduct the UV aging on simplified components of bitumen is very helpful to reveal the UV aging mechanism accurately. In this study, two bitumens were separated into four generic fractions (saturates, aromatics, resins and asphaltenes) respectively by solubility procedures and chromatographic techniques. Both bitumens and their fractions were processed to form a thin film and then aged under UV irradiation for a certain time. The Fourier transform infrared spectra of bitumens and their fractions before and after the UV aging were recorded and quantitatively analyzed based on four structural indexes to evaluate the effect of UV aging on chemical evolution of bitumens and fractions. The results show that the bitumens and their generic fractions all suffer from reactions of oxidation and aromatization during the UV aging. The single fraction separated from the bitumen suffers from more severe oxidation and is more vulnerable to the UV aging than the bitumen itself. Among the four generic fractions, saturates are the most unstable components to be oxidized by the UV aging.