Polyurethane and nano-TiO2 modifiers mitigate aging of asphalt binders by inhibiting aggregation of polar molecules: A molecular dynamics study

The aim of this study was to employ molecular dynamics to investigate how the addition of polyurethane and nano-TiO2 modifiers affects the strengthening mechanism and anti-aging properties of asphalt binders. In this study, asphalt molecular model, nano-TiO2 cluster model, PU molecular model, and PU/nano-TiO2/asphalt molecular model were constructed. The radius of gyration, free volume, diffusion coefficient, and indicators of structural alterations were used to analyze the impacts of PU and nano-TiO2 modifiers on the molecular structure of asphalt. The results indicate that the aging process of asphalt introduces oxygen-containing active functional groups. These groups increase the interaction forces among polar molecules, resulting in the aggregation of polar molecules and the disruption of the original colloidal structure. The spatial barrier effect of polyurethane chains hinders the self-aggregation behavior of asphaltene molecules. Asphaltenes are adsorbed onto the nano-TiO2 clusters, thereby impeding the formation of large-sized polar molecular aggregates. The primary role of polyurethane and nano-TiO2 is to mitigate the aging-induced aggregation of asphaltene polar molecules, preserving asphalt performance. However, it's important to note that asphalt will inevitably undergo aging over time.