Multiscale mechanisms of reactive oxygen species-induced oxidation of SBS-modified asphalt: From physical oxidation diffusion to chemical oxidation reaction

Reactive oxygen species (ROS, ·OH, ·OOH, and O₂) are ubiquitous in urban environments and may significantly accelerate asphalt pavement aging, yet their interactions with asphalt components remain poorly understood. This study combined quantum chemical calculations and molecular dynamics simulations to investigate the chemical reactivity and diffusion behavior of ROS in SBS-modified asphalt (SBSMA). The results show that phenolic groups and sulfur atoms in asphaltenes and resins, branched sulfur atoms and aromatic hydrogen atoms in aromatics, and CC double bonds in SBS are the main ROS attack sites. Among them, hydrogen abstraction from phenolic sites in asphaltenes by ·OH exhibits the highest reaction rate, indicating a dominant pathway in early-stage oxidation. Sulfur-containing sites in aromatic molecules are more reactive toward ·OOH and O₂, suggesting their important role in sulfoxide formation during later oxidation stages. At ambient temperature, ROS preferentially accumulate in highly polar asphaltene regions, whereas elevated temperature promotes a more uniform distribution and stronger site selectivity. ·OH shows the combined characteristics of strong binding and high diffusivity, followed by O₂, while ·OOH exhibits limited diffusion at ambient temperature. These findings provide theoretical support for anti-aging design of asphalt pavements in ROS-rich environments.