Review on molecular dynamics simulation for compatibilities of modifiers with asphalt

The research into the compatibilities of different types of modifiers with asphalt based on the molecular dynamics (MD) simulation was comprehensively reviewed, and the basic principles and methods of MD were introduced. The building of molecular models of asphalt and modifiers and the selection of environmental parameters were summarized. The influences of different evaluation indexes on the compatibility results and the correlation between MD simulation and experimental results were analyzed. Research results indicate that in studying the compatibilities of different types of modifiers with asphalt, the MD simulation can provide atom-level understanding and show its advantages in performance prediction, exploration of multiple interactions, optimization of ratios, and visualization to thus save costs and reduce experimental time. For polymer modifiers, their compatibilities with asphalt are mainly evaluated by indicators including the solubility, diffusion coefficient, mean square displacement and binding energy. For non-polymer modifiers, the evaluation is mainly based on the indicators such as the diffusion coefficient, radial distribution function, and binding energy. The solubility is widely applicable to the polymer-modified asphalt, but the thermodynamic properties of non-polymer modifiers and asphalt are greatly different, with a large dispersion in evaluation results. The diffusion coefficient and binding energy show wide applicabilities in evaluating the compatibilities of polymer and non-polymer modifiers with asphalt. Due to the influences of many factors such as the chemical composition, physical properties, interactions between molecules, and rheological behaviors of asphalt under different conditions, accuracies of model parameters should be verified by sufficient experimental data. The accuracy and reliability of simulation results are affected by these factors, resulting in certain differences in adaptabilities and results of different models. With the advances in computing power and algorithms, the MD simulation accuracy and efficiency improve greatly. Thus, researchers can more accurately simulate the chemical structures and dynamic behaviors of modified asphalt at different temperatures. If the MD is combined with experiments effectively to achieve multi-scale research, it is likely to reveal the compatibility mechanism of modifier with asphalt comprehensively, improve material properties, and expand the application fields.