Multiscale characterisation on the adhesion and selective adsorption at bitumen–mineral interface

The adhesion between bitumen and minerals is essential for the durability of asphalt mixtures, influenced by bitumen composition and mineral structure. The chemical action theory suggests that polar components in bitumen are adsorbed onto the mineral surface, facilitating adhesion. In this study, environmental scanning electron microscopy with energy-dispersive X-ray (ESEM-EDS) is used to analyse bitumen–mineral interfaces at a microscopic level. Elemental analysis reveals selective adsorption of polar substances from bitumen onto the surfaces of four types of minerals. Results show that alkaline rocks (limestone and albite) have a higher adsorption capacity than acidic rocks (granite and quartz). Additionally, treating mineral surfaces with alkaline solutions enhances adsorption. The adhesion properties of bitumen to various minerals are evaluated using the pull-off test. The correlation between ESEM-EDS and pull-off tests demonstrates that the macroscopic adhesion of bitumen to minerals is linked to the microscopic selective adsorption of polar substances.