An investigation toward adhesion characteristics of emulsified asphalt residue–aggregate interface through MD simulation

Abstract

The bonding ability of emulsified asphalt residue-aggregate interface is crucial for improving the pavement performance of emulsified asphalt mixtures. The aim of the study was to explore the adhesion mechanism and characteristics of emulsified asphalt residue-aggregate interface under the different emulsifier contents using molecular dynamics (MD) simulation. Firstly, the emulsified asphalt residue-aggregate interface model was established, and its validity was validated through the related thermodynamic properties. Secondly, the performance-related parameters were employed to discuss the molecular arrangement features of emulsified asphalt residue components on the aggregate surface, and investigate the interfacial adhesion mechanism. Thirdly, the adhesion strength of emulsified asphalt residue-aggregate interface was calculated and evaluated by the adhesion energy. Lastly, the influence of temperature and moisture on the interfacial adhesion strength was further examined through the molecular orientation theory and the electrostatic interaction theory. The results indicate that the addition of emulsifiers could affect the aggregation behaviors and distribution characteristics of asphalt components as observed from performance-related parameters. When compared to relatively high emulsifier content (4–6 %), the molecular arrangement of emulsified asphalt residue components with relatively low emulsifier content (1–3 %) is more similar to that of the base asphalt and exhibits greater interfacial adhesion strength with aggregates. The polar components and emulsifiers in emulsified asphalt residue with relatively low emulsifier content are minor affected by the increase of temperature, which further proving that interfacial adhesion strength is higher at this condition. Meanwhile, emulsified asphalt residue with relatively low emulsifier content is confirmed to have better moisture damage resistance due to the existence of the certain number of Silica-Water(S-W) and Asphalt-Water(A-W) hydrogen bonds near interface. Moisture exhibits more significant influence on the interfacial adhesion strength between emulsified asphalt residue and aggregates according to the results of the average adhesion energy. It is advisable to apply emulsified asphalt with moderate emulsifier content during the actual production process considering the influence of moisture and temperature on the pavement performance of emulsified asphalt mixtures.