Molecular insights into the role of heteroatoms on the thermal and rheological behaviour of asphalt binders

Asphalt binders play a central role in road infrastructure, and their performance is heavily influenced by their chemical composition and response to temperature changes. In this study, we used all-atom molecular dynamics simulations to explore how variations in the chemical structure, particularly the presence of heteroatoms such as oxygen, nitrogen, and sulfur, affect the behaviour of asphalt at the molecular level. We designed a set of surrogate asphalt models based on realistic SARA fractions, including a baseline model and six modified versions with elevated heteroatom contents. Among these, the AM-3O, AM-3N, and AM-3S models were selected for a detailed analysis because their densities closely match those typically reported in experiments. By simulating these models across a wide temperature range (100–533.15 K), we captured important thermal and physical trends, including changes in density, volume, diffusivity, and viscosity. The three systems transitioned through different mechanical states, from glassy to viscoelastic to Newtonian fluid, with glass transition temperatures (Tg) clustered around (265–272)±6 K. Although the chemical composition of asphalt, heteroatom content, and type affect the overall density, they had only a modest effect on Tg and viscoelastic-to-Newtonian fluid transition temperatures (TX). These results demonstrate how variations in heteroatom chemistry influence the molecular packing and transport behaviour of asphalt binders. The findings provide molecular-level insights that may assist future studies aimed at designing improved asphalt materials.