Thermal ageing mechanism of a natural rock-modified asphalt binder using Fourier Transform Infrared Spectroscopy analysis

In this paper, Fourier-transform infrared (FTIR) spectroscopy was used for the microanalysis of base asphalt modified with natural rock asphalt as the asphalt modifier. A Pen 70 asphalt was selected and natural rock asphalt modifiers (2%, 4%, 6%, and 8%) were added to prepare different asphalt samples. Macroscopically, the performance indexes of five kinds of asphalt before and after short-term ageing and the changes of each index with the content were tested. The changes in characteristic functional groups of natural rock modified asphalt before and after thermal ageing were analyzed by FTIR. The ageing degree of asphalt was judged by qualitative and quantitative analysis, and the ageing behavior and mechanism of asphalt were revealed from the microscopic point of view, establishing the relationship between macro and micro, combined with the Dynamic Shear Rheometer (DSR) test. The results showed that, with the increase of the content, the penetration and ductility decrease, and the softening point increases, indicating that the viscosity and thermal stability of asphalt increase after adding natural asphalt. The asphalt before and after short-term ageing follows this law. The short-term ageing process was mainly characterized by physical compatibility and volatilization of light components. A small amount of carbonyl group was formed, and a small number of components were dehydrogenated to olefin. In the long-term ageing process, the long-chain hydrocarbon decomposition of the polymer generated alkyl (CH3), and the polar molecule reacted with oxygen to generate a large number of carbonyl groups (C=O) and sulfone groups (S=O). In addition, according to the carbonyl index CI and sulfoxide index SI, the ageing degree of the modified asphalt was less than that of the base asphalt. Meanwhile, it can be determined that the carbonyl index was the smallest and the ageing resistance was the best when the content of natural rock is 6%.