The stability of emulsified asphalt and interfacial behavior of emulsified asphalt-aggregate based on molecular dynamics simulation: A review

Abstract

To deeply analyze the stability of emulsified asphalt and the interfacial behavior of emulsified asphalt-aggregate, this paper reviews the related research progress of emulsified asphalt system based on molecular dynamics (MD) simulation. The construction and validation methods of models for emulsified asphalt and its residues are introduced. The stability mechanisms of emulsified asphalt and the factors affecting its stability are summarized. Furthermore, the distinct roles of emulsifier molecules, water molecules, and asphalt molecules in diffusion on aggregate surfaces are analyzed. The adsorption and demulsification behaviors of emulsifier aqueous solution and emulsified asphalt on aggregate surfaces are effectively evaluated by parameters such as interfacial interaction energy, adhesion energy, radial distribution function, relative concentration distribution, diffusion coefficient, and coordination number. The failure modes of the emulsified asphalt residue-aggregate system are summarized. Finally, the challenges and development trends of MD in emulsified asphalt systems are proposed. The research status shows that MD simulation has broad application prospects in emulsified asphalt system. The molecular structure and dosage of emulsifier, water molecules, asphalt phase structure and modifier all affect the stability of emulsified asphalt. In the emulsified asphalt-aggregate system, water molecules initially tend to move toward the aggregate, driving the hydrophilic group of the emulsifier interacts with the aggregate. While the lipophilic group remains in the asphalt, facilitating the diffusion of asphalt molecules on the aggregate. The adsorption, demulsification, and adhesion behaviors of emulsified asphalt on aggregate surfaces are closely related to the structure and type of emulsifiers and aggregates. The failure modes of the emulsified asphalt residue-aggregate system include adhesive failure between residues and aggregates, cohesive failure within residues, and residue stripping in the presence of water. Future research should focus on refining the molecular models of emulsified asphalt and its residues to better utilize molecular simulations in explaining pavement macroscopic performance. Furthermore, simulation methods such as quantum mechanics are integrated to explore the chemical interactions between modifiers and emulsified asphalt, providing a molecular-level basis for modifier selection and formulation optimization. In addition, the quantitative study of demulsification speed of emulsified asphalt on aggregate surface should be focused based on the molecular level. The effect of cement hydration on the interfacial behavior of emulsified asphalt-aggregate system should be further explored to fully understand and optimize the performance of emulsified asphalt mixture.