Micro-characterization of the adhesion properties and mechanisms at the asphalt-silica aggregate interface under combined thermal-oxygen aging and chloride salt erosion

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In this investigation, various Atomic Force Microscopy (AFM) probes were used to characterize changes in the adhesion properties of aged asphalt under different concentrations of chloride salt. The characterization included analyzing the surface morphology, roughness parameters, height-height correlation function (HHCF), and force-distance curves of the asphalt. Additionally, Molecular Dynamics (MD) simulation was employed to reveal the underlying mechanisms that govern changes in adhesion properties between aged asphalt and aggregate when subjected to chloride salt erosion. Interfacial erosion and internal erosion models were constructed to facilitate a comprehensive analysis from multiple perspectives. The results demonstrate that chloride salts interact with the interface between asphalt and silica aggregates, engaging in competitive adsorption with the asphalt. The strength of this competitive adsorption is influenced by the constituents of the asphalt and the concentration gradient of chloride salts both within and outside the asphalt matrix. Under this concentration gradient, polar components are attracted to the asphalt surface by chloride ions, forming triangular adsorption structures with water molecules and aggregates such as asphaltene. Components with lower polarity exhibit distinct distributions and diffusion states due to variations in molecular weight and spatial configuration. As the concentration of chloride salts increases, the concentration gradient intensifies, resulting in enhanced transformations, migrations, and dissolutions of asphalt components. Consequently, the micro-morphology of the asphalt tends to smoothen, the HHCF undergoes significant modifications, roughness decreases, and the adhesion performance between asphalt and aggregate weakens. Moreover, at higher concentrations, the formation of precipitated chloride salt crystals disrupts the continuity of the asphalt, further compromising interfacial adhesion performance. This study is expected to provide theoretical guidance for the modification of asphalt and the improvement of asphalt pavement lifespan in complex service environments.