Molecular-Level Analysis of Oxygen and Asphalt Behavior on Aggregate Surfaces

The diffusion of oxygen molecules significantly influence the rate and extent of asphalt's oxidative aging. This research delves into the dynamic diffusion of oxygen within asphalt, examining the effects of temperature, water, aggregate types, and oxygen concentration. It establishes models for the mixed diffusion of oxygen and asphalt molecules and layered diffusion models for oxygen/(water) asphalt (aggregate) to simulate the dispersion processes of oxygen molecules within and into asphalt. Molecular dynamics simulations uncover the subtle interplay of these factors on oxygen distribution and their impact on asphalt's oxidative aging. By analyzing the molecular dynamics parameters (relative concentration, diffusion coefficient, and radial distribution function) of molecular structures within the model, the study reveals that, unlike diffusion in a vacuum, oxygen diffusion in asphalt follows a quadratic function with temperature changes. The presence of moisture decreases the concentration of oxygen within the asphalt, potentially reducing the degree of oxidation. Aggregates exhibit adsorption effects on oxygen and asphalt components, with their properties also influencing molecular mobility patterns. Oxygen accumulation at the aggregate/asphalt interface may increase the risk of damage. This research contributes to a deeper understanding of oxygen diffusion behavior during asphalt's oxidative aging process, offering insights for improving asphalt durability and developing antioxidants through managing oxygen diffusion.