Molecular Dynamics Study Of Diffusion Behavior Of Virgin And Recycled Asphalt Binder

For the asphalt reclaimed technology,the molecular diffusion between virgin asphalt binder,aged asphalt binder and rejuvenator is an key issue,which directly affects the appropriate new asphalt binder grade and its dosage.It also has great importance to the quality of the reclaimed asphalt pavement and its performance.To this end,the molecular dynamics method was used to comprehensively study the actual blending status of RAP and virgin binder from the molecular scale.Virgin and aged asphalt molecular model were constructed to simulate the diffusion and interaction mechanism between virgin asphalt binder,aged asphalt binder and rejuvenator,and analyze the macroscopic physical properties of the reclaimed asphalt mixture as well.Firstly,the average molecular model was selected to construct the molecular model of virgin asphalt binder.The molecular model of aged asphalt binder was constructed by adding functional groups.Two kinds of molecular models: aromatic and chain were selected as representatives of rejuvenator.In all MD simulations,the COMPASSII force field,NVT and NPT ensembles were used in the simulation.Periodic boundary conditions were applied.The Nose-Hoover thermostat and Andersen barostat were employed to control the temperature and pressure respectively.The Atom based method was used to calculate the van der Waals non-bonding interaction,and the Ewald method was used to calculate the electrostatic non-bonding interaction.Secondly,the thermodynamic properties of molecular models of asphalt binder and rejuvenator were verified.Density,surface free energy,work of cohesion,cohesive energy and solubility were calculated.The calculated results were compared with the actual experimental data and found to be consistent.It suggested that the constructed model can well characterize the properties of asphalt and rejuvenator materials and is suitable for the next simulation calculation.Then,based on the process of recycling asphalt in actual engineering,the two-layer model of virgin and aged asphalt binder was developed to simulate the inter-diffusion of virgin and aged asphalt binder.From the perspective of thermodynamic properties,the density and relative concentration of the two-layer model were calculated and analyzed.From the energy point of view,the van der Waals potential energy,electrostatics potential energy and interaction energy of the two-layer model were calculated and analyzed.The effects of temperature and rejuvenator on the inter-diffusion process were also analyzed.Finally,a series of studies on the interaction of reclaimed asphalt were carried out.The mixture model was built and factors affecting the interaction of reclaimed asphalt were also explored by calculating the parameters such as diffusion coefficient,radial distribution function and interaction energy.Studies have shown that the molecular migration rate of virgin asphalt is greater than that of aged asphalt,and the increase of temperature and the addition of rejuvenator can increase the diffusioncoefficient of asphalt molecules.The aging process will weaken the self-aggregation phenomenon of the asphalt molecules,however,the addition of the rejuvenator can restore the self-aggregation tendency of the aged asphalt molecules to some extent and evenly distribute the new and old asphalt molecules around each other.The addition of rejuvenator will weaken the interaction energy between virgin and aged asphalt.The greater the amount of rejuvenator was added,the weaker the mutual attraction between the virgin and aged asphalt was,but the interaction between the rejuvenator and the aged asphalt will increase.