Molecular Dynamics Simulation Of Asphalt-aggregate Interfacial Interaction

Asphalt mixture is a kind of multiphase composite material,which is mainly composed of aggregate,filler and asphalt.Due to the natural weakness of multiphase composite at its interface,the interfacial bonding strength between asphalt and aggregates will directly affect the performance of asphalt mixture,thus affecting the overall service life of asphalt pavement.Past research on the interfacial interaction between asphalt and aggregates mainly focuses on the macro experimental level,and few studies explore its interaction mechanism from the molecular level.In this study,the molecular dynamics simulation was used to investigate the fundamental molecular interaction between asphalt and aggregates.Firstly,two representative minerals(calcite and α-quartz)were selected to obtain their surface models,including three commonly exposed surfaces of α-quartz {001},{100},{101}and three natural cleavage surfaces of calcite {104},{214},{018}.The interfacial models between asphalt and aggregates were established by combining the surface model and 12-component asphalt model respectively,followed by simulated annealing to get the stable models.The adhesion strength and interaction mechanism of different interfaces were obtained through dynamic calculation.The simulation results show that there is a significant difference in adhesion strength between anisotropic mineral surfaces and asphalt.For the α-quartz-asphalt interfacial model,the adhesion strength is mainly composed of van der Waals interaction,while van der Waals interaction and electrostatic interaction are both important for calcite-asphalt interfacial models.The adhesion strength between calcite and asphalt is better than that of α-quartz,and the interfacial bonding strength is closely related to the atomic density and the number of broken bonds on the mineral surfaces.Secondly,in order to explore the influence of moisture on the interfacial interaction between asphalt and aggregates,the aggregate-water,asphalt-water-aggregate interfacial models were established to study the interaction mechanism between the interfaces.The improved Energy Ratio(ER)were established to evaluate the moisture susceptibility of asphalt mixtures.In addition,the wettability of anisotropic mineral surfaces was studied by simulating the diffusion behavior of nano water droplets on anisotropic mineral surfaces.The wettability of mineral surfaces was evaluated by the contact angle.The simulation results show that: 1)the anisotropic mineral surface has a significant effect on the interfacial bonding and moisture sensitivity of asphalt mixtures;2)the hydroxyl groups on α-quartz surfaces can significantly improve the surface hydrophilicity,thus increasing the possibility of water damage;3)the freshcleaved calcite surface is the key factor to increase the moisture susceptibility of asphalt mixtures.Finally,the effect of asphalt oxidative aging on the thermodynamic properties and interfacial adhesion was studied by molecular dynamics simulation.The oxidative aged asphalt model was established based on previous aging simulation experiments.The glass transition behavior of asphalt before and after oxidative aging was studied by simulating the quenching process.Fractional free volume,mean square displacement were used to characterize the effects of asphalt aging on molecular diffusion behavior.The results show that the free volume between asphalt molecules decreases and the diffusion of asphalt molecules is inhibited,resulting in a higher glass transition temperature of aged asphalt.In addition,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.