Molecular dynamics models to investigate the diffusion behavior of emulsified asphalt

The utilization of emulsified asphalt is widespread in the recycling of asphalt pavement due to its eco-friendliness and energy efficiency. While numerous research studies have been conducted on the mixture design and strength assessment of emulsified asphalt, the mechanism by which it diffuses and adheres to the aggregate surface remains inadequately comprehended. This study developed molecular dynamics models to investigate the diffusion behavior of emulsified asphalt on the aggregate surface to clarify the role of emulsifier, water, and asphalt in the adsorption process from a molecular perspective. Interface models are established according to the diffusion state for interfacial adhesion evaluation. The results show that the movement of water molecules is the driving force for the entire emulsified asphalt to adsorb to the aggregate surface, whether the aggregate is silica or reclaimed asphalt pavement (RAP). Compared with anionic surfactant Sodium Dodecylbenzene Sulfonate (SDBS), cationic emulsifier Cetyltrimethylammonium Chloride (CTAC) has a better affinity, stronger adsorption, and higher interfacial adhesion energy with silica. Compared with RAP, emulsified asphalt is more readily adsorbed to the surface of silica. It is concluded that emulsifiers have two distribution conformations during the adsorption process, delamination, and aggregation, with delamination exhibiting stronger interface strength with silica than aggregation. When the emulsified asphalt spreads on the RAP surface, the penetration of water molecules into the aged asphalt layer in the RAP structure reduces the structure's water resistance. These results can provide a molecular perspective for understanding the internal structure of emulsified cold recycle mixture (ECRM) and link the adsorption behavior of emulsified asphalt on aggregate surfaces with the internal interface strength of ECRM.