Investigating the aging mechanism of asphaltene and its dependence on environmental factors through AIMD simulations and DFT calculations.

To understand the complex aging mechanism of asphalt and its dependence on environmental factors, the chemical reactivity of asphaltene during aging under different environmental conditions was studied through first-principles molecular simulations and density functional theory calculations. The aging of asphaltene was demonstrated to involve a series of subreactions along different pathways on the asphaltene molecules, including hydrogen abstraction from carbon, formation of polar groups, aromatization of cycloalkanes, and homolysis of side chains. These subreactions occurred with different free-energy barriers and, therefore, had different kinetic rates. Asphaltene aging was found to be slightly accelerated in the presence of water owing to the improved electron transfer ability of the asphaltene molecule in an aqueous solvent. Under ultraviolet radiation, the asphaltene molecule transitioned to an excited state with an excitation energy of 348.7 kJ/mol, significantly increasing its aging rate. This work bridges the gap between electronic-scale modeling and diversified experimental observations related to asphalt aging and is expected to provide theoretical guidance for strategies to prevent or delay the aging-induced failure of asphalt pavements.