The effect of composite curing agent ratio on the photooxidative aging behavior of epoxy asphalt based on molecular dynamics simulation

In order to explore the effect of composite curing agent ratio on the photooxidative aging behavior of epoxy asphalt with an acidic composite curing system, three curing agent ratios of epoxy asphalt were prepared to obtain different cross-linking network densities. The prepared epoxy asphalt was subjected to photooxidation aging for 240 h at 60 ℃. Fourier transform infrared (FTIR) and elemental analysis tests were conducted to determine the evolution of chemical components during photooxidative aging. Based on the chemical components before and after aging, molecular models of photooxidation aged epoxy asphalt with different curing agent ratios were constructed. The mean square displacement (MSD) of oxygen atoms and the oxygen uptake of each component were calculated to study the diffusion behavior of oxygen atoms and the oxidation degree of each component under various cross-linking networks. Glass transition temperature (Tg) and interaction energy were determined to characterize the thermodynamic properties and interaction between asphalt phase and epoxy resin phase of epoxy asphalt before and after aging. The radial distribution function (RDF) was determined to simulate the distribution of asphaltene and epoxy resin crosslinked networks in different cross-linking networks. The results show that the formation of carbonyl groups, alcohol hydroxyl groups, and the fracture of methylene groups was observed during the photooxidative aging process of epoxy asphalt. The rise in the proportion of anhydride curing agents improved the stability of the chemical components in epoxy asphalt under photooxidation aging. High cross-linking density and methylene fracture weakened the diffusion ability of oxygen atoms in epoxy asphalt due to a reduction in free volume. In addition, photooxidation aging had a negative impact on the low-temperature performance and interaction between asphalt phase and epoxy resin phase of epoxy asphalt. However, a high content of acid anhydride alleviated the damage of photooxidation aging to low-temperature performance. Photooxidation aging developed the polar functional groups of epoxy asphalt, promoting the stacking of asphaltene under a high content of dicarboxylic acid curing agent, while breaking the stacking of asphaltene under a high content of acid anhydride curing agent.