Study on the multiscale adhesive properties between asphalt and aggregate

Abstract

Adhesion between aggregate and asphalt is an important factor affecting the road performance of the asphalt mixture. It can be mainly attributed to the microscopic forces between the contacting interfaces, including the physical and chemical interactions between interfaces, which are subject to the surface micromorphology (SMM) and chemical composition of the materials, respectively. In this study, the SMM parameters and surface energies of the aggregate and asphalt were investigated using confocal microscopy and atomic force microscopy (AFM), respectively. The macroscopic adhesion strength between aggregate and asphalt was tested via pull-off tests, and the influences of the SMMs and surface energies of the materials on the macroscopic adhesion strength were investigated. Finally, the multiscale adhesion mechanisms between aggregate and asphalt were explored. Results indicated that adhesion between aggregate and asphalt binder was mainly attributed to the chemical interaction that was dominated by asphalt surface energy. The physical interaction was related to the SMMs of asphalt and aggregate. The roughness of the aggregate SMM was beneficial for improving the adhesion, whereas the roughness of the asphalt SMM was unfavorable. Among the four fractions of asphalt, the asphaltenes and resins had a significant influence on the surface energy of asphalt, which increased with an increase in the resin content, and conversely decreased with an increase in the asphaltenes content. The aggregate surface energy was mainly affected by the SiO2 and CaO content, and decreased with an increase in the SiO2 content, and increased with an increase in the CaO content.