Molecular dynamics simulation on oxidation process and interfacial performance of foamed asphalt binders based on ReaxFF force field

Asphalt can deteriorate and age due to exposure to environmental conditions. This ageing reduces pavement performance and recycling waste pavement is relevant for environmental protection. The oxidation process, properties and interfacial behaviour of asphalt binders and foamed asphalt binders were discussed with the classical molecular dynamics (MD) simulation and reactive force field molecular dynamics (ReaxFF MD) simulation, as well as mineral aggregate molecular systems. The oxidized models for each asphalt molecule were proposed, which closely matched actual experimental study results. The simulation results showed that sulfur atoms oxidized the fastest, followed by benzyl carbon. As the degree of oxidation increased, the viscosity and glass transition temperature of asphalt molecules also increased. The interfacial energies of various systems were analysed, such as foamed asphalt-aged asphalt, asphalt–aggregate and asphalt-recycled aggregate. It was found that the adhesion of asphalt-aged asphalt decreased due to the presence of water, but this phenomenon was not observed in the asphalt-recycled aggregate interface when the water content was less than 2%. The mean square displacement results showed that 3% or less water content facilitated the diffusion and movement of molecules in asphalt-recycled aggregate systems, whereas, in asphalt–aggregate systems, only 1% water content was sufficient.