Molecular dynamics analysis of oxidative aging effects on thermodynamic and interfacial bonding properties of asphalt mixtures

Understanding the mechanisms of asphalt aging and aging related properties is of significant importance. In this paper, molecular dynamics (MD) simulation was employed to study the effects of asphalt oxidative aging on the thermodynamic and interfacial bonding properties of asphalt mixtures. The virgin and aged AAA-1 asphalt models, validated based on physicochemical properties, were constructed in this study. The glass transition behaviors of asphalt models were investigated by simulating a gradual cooling process. It is found that asphalt oxidative aging increases the intermolecular interaction, thus resulting in a higher glass transition temperature. Restrictions of dihedral torsion and non-bond interaction at a low temperature are primary reasons causing the glass transition behavior. The volumetric property, fractional free volume (FFV) among asphalt molecules was studied with an empirical calculation method. The results show that the FFV-temperature behavior for both virgin and aged asphalt models exhibits a glass transition phenomenon akin to the specific volume-temperature relationship. In addition, the asphalt diffusion behavior before and after oxidative aging was evaluated by their mean square displacements (MSD). The result indicates that oxidative aging causes a reduction of free volume, and thereby slows down asphalt molecular diffusion. Finally, the adhesion behavior and moisture susceptibility considering asphalt aging effects were investigated to provide a better understanding of the mechanism of asphalt oxidative aging and aging related phenomena.