Nanomechanical-atomistic insights on interface interactions in asphalt mixtures with various chloride ion erosion statuses.

Coastal asphalt pavements are highly susceptible to sea salt erosion, which leads to a significant decrease in road performance and durability. However, the interface micro-adhesion mechanism of the asphalt-aggregate composites under chloride ion erosion is still not fully understood. Herein, using the silica microsphere Atomic Force Microscopy (AFM) modified tip and asphalt sample with chloride ions as a surface, we report the effect mechanism of chloride ion erosion on the interface adhesion behavior of asphalt-silica composites by AFM from the atomistic scale. The chloride ion erosion mechanism was further supported by molecular dynamics (MD) simulations. Due to the erosion effect of chloride ions, the structure evolution of the asphalt film surface will occur, and the weak adhesion gradient zone will be formed on the surface of the asphalt film. The concentration effect of chloride ions accelerates the formation of adhesion gradient zones, which are unstable and evolve over erosion time. Due to the presence of these adhesion gradient zones, water molecules will more easily penetrate the asphalt membrane and enter the asphalt-silica interface through adsorption and diffusion, thereby weakening the interface adhesion ability between the asphalt and the aggregate. Furthermore, the distribution and diffusion of asphalt fractions on the aggregate surface also affect the adhesion behavior evolution of asphalt-silica composites induced by chloride ion erosion. The evolution in the spatial distribution of fractions may be related to the formation of interfacial adhesion gradient zones. This study outcome has important theoretical significance for promoting the sustainability of asphalt pavements and for guiding pavement deicing.

aRDG Analysis of Asphaltene Molecular Viscosity and Molecular Interaction Based on Non-Equilibrium Molecular Dynamics Simulation.

Understanding the noncovalent (weak) interactions between asphaltene molecules is crucial to further comprehending the viscosity and aggregation behavior of asphaltenes. In the past, intermolecular interactions were characterized indirectly by calculating the radial distribution function and the numerical distribution of distances/angles between atoms, which are far less intuitive than the average reduced density gradient (aRDG) method. This study selected three representative asphaltene molecules (AsphalteneO, AsphalteneT, and AsphalteneY) to investigate the relationship between viscosity and weak intermolecular interactions. Firstly, a non-equilibrium molecular dynamics (NEMD) simulation was employed to calculate the shear viscosities of these molecules and analyze their aggregation behaviors. In addition, the types of weak intermolecular interactions of asphaltene were visualized by the aRDG method. Finally, the stability of the weak intermolecular interactions was analyzed by the thermal fluctuation index (TFI). The results indicate that AsphalteneY has the highest viscosity. The aggregation behavior of AsphalteneO is mainly face-face stacking, while AsphalteneT and AsphalteneY associate mainly via offset stacking and T-shaped stacking. According to the aRDG analysis, the weak interactions between AshalteneT molecules are similar to those between AshalteneO molecules, mainly due to van der Waals interactions and steric hindrance effects. At the same time, there is a strong attraction between AsphalteneY molecules. Additionally, the results of the TFI analysis show that the weak intermolecular interactions of the three types of asphaltene molecules are relatively stable and not significantly affected by thermal motion. Our results provide a new method for better understanding asphaltene molecules' viscosity and aggregation behavior.

Revealing compatibility mechanism of nanosilica in asphalt through molecular dynamics simulation.

The compatibility between asphalt and nanosilica (nano-SiO2) is critical to determine the performance of nano-SiO2-modified asphalt. However, a comprehensive understanding of the compatibility behavior and mechanism of asphalt components and nano-SiO2 in the modified asphalt is still limited. In this study, the compatibility was revealed through molecular dynamics (MD) simulation. Virgin asphalt, nano-SiO2-modified asphalt, and oxidation aged asphalt models produced with the COMPASS force field; meanwhile, the proposed models were validated by comparisons with reference data. The compatibility of asphalt and nano-SiO2 was analyzed by solubility and the Flory-Huggins parameters and interaction energy. Results show that the solubility parameters decreased with the increase of system temperature while increased with the asphalt's oxidation level increase. Meanwhile, the compatibility of the asphaltene, resin, and aromatic components in asphalt is better than the compatibility with saturates, which may be due to saturates being volatile; however, the compatibility of the nano-SiO2 and saturates is much better than those with asphaltene, resin, and aromatic components. The incorporation of nano-SiO2 alleviates the volatilization of saturates. The present results provide insights into the understanding of the compatibility behavior and mechanism of nano-SiO2 and asphalt components.