Micromorphology and Micromechanical Properties Evolution of Bitumen and Bitumen Fractions Using Atomic Force Microscopy Considering Temperature Effect

Bitumen is the residue of crude oil distillation. More understanding of bitumen can help to improve its effective application in industrial engineering, and this in turn reduces the energy consumption. This study investigated the microstructure and micromechanical properties of four types of bitumen as well as the SARA (saturates, aromatics, resins, and asphaltenes) fractions using quantitative nanomechanical property mapping equipped in an atomic force microscope with the temperature ranging from 25 to 65 degrees C. Differential scanning calorimetry analysis was also conducted to link the thermal behavior of bitumen with its micromorphology evolution at different temperatures. The results show that all studied bitumens have similar glass and phase transitions, but their properties at the microscale varied significantly with the types of bitumen. In addition to the bee structures, some special structures, named big structures, valleys, and peaks, were observed in the surface micromorphology of bitumen. Among them, bee and peak structures faded away, while big and valley structures became dense with the temperature rising from 25 to 65 degrees C. In addition, the bitumen with bee structures was rougher and more sensitive to temperature than that without bee structures. The research on the origin of bee structures, which was carried out by contrastive analysis of the morphology of bitumen and SARA fractions, shows that the content of aromatics, asphaltenes, and wax had an obvious effect on the bee structure formation, and the bee structures were only found in aromatics. Temperature had a significant influence on the adhesion of polymer modified bitumen compared to the virgin bitumen, and the moduli of all types of bitumen decreased obviously with the increase of temperature. It was also found that the bitumen morphology and mechanical property maps correspond well: the areas with special structures showed higher moduli and lower adhesion.