Abstract
The asphalt mastic–aggregate interface plays an essential role in determining the service performance of asphalt mixtures. The objective of this paper was to investigate the adhesion behaviors and mechanism between asphalt mastic and aggregate based on molecular dynamic (MD) simulations. First, the asphalt mastic model considering the actual mass ratio of filler to asphalt (F/A) condition was established and validated in terms of thermodynamic properties. Second, the molecular arrangement characteristics of polar components on the aggregate substrate were analyzed by radial distribution function (RDF), relative concentration (RC), and mean square displacement (MSD). Third, the interfacial adhesion ability between asphalt and aggregate was quantitively evaluated based on the work of adhesion. Finally, the coupling effect of moisture and temperature on interfacial adhesion behaviors was investigated to explore the adhesion failure characteristics of the asphalt–aggregate interface. The results demonstrate that the thermodynamic properties could be employed to validate the reliability of the asphalt mastic model. The self-aggregation degree of polar components in base asphalt could be significantly increased with the addition of silica particles, exhibiting a change of configuration from “parallel arrangement” into “stack distribution” due to the high polarity of silica particles. The polar components in asphalt mastic exhibit a more uniform distribution state and lower mobility capability than base asphalt owing to the adsorption effect of silica particles. Silica particles with amounts of residual charges could significantly increase the electrostatic energy of the asphalt mastic–aggregate interface, contributing to an improvement of the adhesion between asphalt mastic and aggregate. The increase of temperature enhances the work of adhesion of the asphalt mastic–aggregate interface, which is opposite to that of the base asphalt–aggregate interface. The asphalt mastic exhibits a greater sensitivity to interfacial moisture damage than base asphalt. The findings would provide insights into a better understanding on the micro adhesion mechanism of the asphalt mastic–aggregate interface.
Highlights
During the long-term service period, asphalt mixtures are extremely prone to damage due to environmental factors and vehicle loads [1,2,3]
The thermodynamic properties including density, glass-transition temperature (Tg ), and cohesive energy density (CED) of two kinds of asphalt material models were discussed to validate whether the molecular simulation method with the COMPASS force field parameters is suitable for describing the characteristics of base asphalt and asphalt mastic
The densities of base asphalt and asphalt mastic were calculated during the NPT ensemble for 500 ps at 1 atm and their values gradually stabilize as the optimization process approaches 500 ps, as shown in Figure 3, at which the densities of base asphalt and asphalt mastic tend to 0.998 g/cm3 and 1.371 g/cm3, respectively
Summary
During the long-term service period, asphalt mixtures are extremely prone to damage due to environmental factors and vehicle loads [1,2,3]. The presence of moisture, aging, and temperature, among others, would dramatically reduce the asphalt–aggregate interfacial bonding strength, leading to the deterioration of the service performance of asphalt mixtures [6,7,8,9]. Deeply understanding adhesion behaviors and improving adhesion ability of the asphalt–aggregate interface are of great significance for reducing the occurrence of various distresses and prolonging the service life of asphalt pavement. The mechanical theory describes adhesion as the mechanical interlock between the asphalt binder and aggregate surface. The chemical theory indicates that the chemical reaction between acid functional groups in asphalt and alkaline active components on the aggregate surface makes a great contribution to the interfacial bonding ability. As for evaluation methods, the adhesion properties of the asphalt–aggregate interface could be quantitively evaluated by different methods, especially the boiling method, which has been commonly utilized as a standard method [15]
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