Research on the evolution of adsorption behavior of asphalt and aggregate surface and its influencing factors

The adsorption between asphalt and aggregate surfaces is a crucial factor in the formation of the asphalt mixture structure, directly affecting the strength, stability, and aging rate of the mixture. This study aims to explore the physical-chemical bonding process between asphalt and aggregates and establish a reliable expression for asphalt adsorption on aggregate surfaces. The optimal wavelength and concentration of asphalt-toluene solutions were determined through Strategic Highway Research Program (SHRP) net adsorption tests. Then the aggregates' composition, shape, and texture properties were evaluated using a scanning electron microscope (SEM), needle-like content, and gray-level co-occurrence matrix. Finally, the impact of temperature, asphalt type, aggregate grain size, and surface texture on the adsorption evolution was studied based on the SHRP net adsorption test. Results showed significant differences in surface morphology among the four types of aggregates. Quartz exhibited the highest smoothness, while albite showed a high degree of roughness despite its complex surface morphology. Increasing temperature led to a decrease in the total adsorption capacity of the aggregates, especially for quartz and elpidite. The inflection points of the adsorption amount of calcite and albite shifted backward with 90# asphalt compared to 70# asphalt, indicating both physical and chemical adsorption. Additionally, changes in specific surface area had a more pronounced effect on the adsorption amount. The presence of a rich texture structure significantly increased the pre-sorption rate of the aggregates and ultimately influenced the adsorption amount. The research findings provide insights to more fully understand the evolution of adsorption behavior between asphalt and aggregate surfaces.