Use of molecular dynamics to investigate diffusion between virgin and aged asphalt binders

The incorporation of recycled (aged) binder into virgin asphalt has become more popular in asphalt paving industry nowadays. However, the exact mechanism of the diffusion process between virgin and aged binders is still largely unclear. This paper presents a study in which molecular dynamics (MD) simulation was employed to investigate the diffusion between virgin and aged binders. Two asphaltic models with three components including asphaltenes, resin, and oil were built with different components ratio. The model of aged binder was constructed by increasing the asphaltenes ratio on the basis of virgin binder. The results of simulation was verified by GPC and both show that the diffusion of large molecules in asphalt was a critical factor for the diffusion of binders in that it was more susceptible to the changes of temperature. In an inter-diffusion model of virgin and aged binders, the diffusion coefficients of binders were not only determined by the diffusion ability itself, but also influenced by the properties of the diffusion acceptor. Based on this finding, the effect of different sequence of adding rejuvenator during recycling of asphalt mixtures was investigated. The result shows that adding rejuvenator into aged binder first could accelerate the inter-diffusion rate between virgin and aged binder in maximum level, thus increased the efficiency of recycling.