Ultraviolet aging mechanism of asphalt molecular based on microscopic simulation

In order to reveal the nature of the Ultraviolet aging(UV-aging) behavior of asphalt molecules, the dynamic behavior of asphalt microstructure during ultraviolet aging was simulated by Materials Studio software. The effect of UV aging on the transformation, aggregation and motion state of asphalt microstructure is analyzed by the changes in energy, microstructural morphological variation, glass transition temperature and viscosity of the asphalt molecular system. The results show that the Satruate and Aromatic provide the active force for the asphalt molecules, the Asphaltene and Resin provide the bonding force for the asphalt molecules. As the UV aging progresses, the lightweight components of the asphalt molecule gradually transform into heavy components. UV aging enhances the bonding degree of asphalt molecules by increasing the heavy components in the asphalt molecules and increasing the distribution width between the asphalt molecule components, which improves the high-temperature resistance of asphalt. At the meantime, the UV aging causes the asphalt molecular movement state to solidify at low temperature so that the rheological behavior is difficult to occur by reducing the lightweight component and free volume of the asphalt molecule and increasing the glass transition temperature, which reduces the low-temperature resistance of asphalt. In addition, among the factors affecting the viscosity of asphalt molecular, the degree of effect of the molecular structure and molecular weight is significantly greater than the molecular activity. Adding short-chain alkanes, multi-branched long-chain alkanes and preventing the synthesis and aggregation of condensed nucleus compounds in the UV-aged asphalt molecule could effectively reduce the viscosity of the asphalt and improve the flowability of the asphalt, thus enhancing the low-temperature resistance of UV-aged asphalt. The results of the study contribute to the understanding of the characteristics of changes in the microstructural pattern and dynamic behavior of asphalt molecules during UV aging, and achieve interpretation and prediction of changes in asphalt properties at the microscopic level.