Microstructural evolution of asphalt induced by chloride salt erosion

Abstract

A salt-eroded environment can have a significant negative impact on asphalt pavements, especially in the salt-rich regions of east and west China. This research examines the microstructural evolution of asphalt binders due to chloride salt erosion through atomic force microscopy (AFM). The morphology, roughness parameters, statistical functions, lateral correlation length (ξ), interface width (ω), and fractal dimension (D_f) are used to study the asphalt surface after chloride treatment. Results from AFM show that chloride salt erosion induces the evolution of the surface local microstructure of the asphalt. The presence of chloride salts will form an unstable amorphous film soluble in water on the surface of the asphalt to wrap the bee-structure. Once the amorphous membrane is destroyed, the bee-structure is re-exposed. As the chloride salt concentration increases, the surface roughness decreases, which is manifested as a decrease in root mean square roughness (S_q). The erosion effect of chloride ions has a significant influence on the ξ and ω of the asphalt samples. The two spatial parameters ω and ξ can provide precise information about the asphalt surface texture together with S_q. Furthermore, the fractal dimension can better reflect the evolution of bee-structures with chloride salt concentration and erosion time. The study results shed light on explaining the essential role of the microstructural evolution of asphalt films which are known as chloride salt erosion.