Molecular Insights into the Adsorption Configuration of Bitumen Colloidal on Aggregate Surface

The interaction between bitumen colloidal and mineral aggregate is complicated owing to an intricate interplay of bitumen chemistry, aggregate mineralogy, and surface topography. Identifying the adsorption configuration of bitumen-aggregate interface has been a longstanding challenge in interface science and material engineering. In this paper, we report a mechanistic study using molecular dynamics simulation to uncover the adsorption configuration of bitumen-aggregate interface at the molecular scale and how aggregate mineralogy affects it. The results show that the adsorbed bitumen layer is densely distributed compared to bulk bitumen, and its structure is a superposition of two configurations: the layered configuration in the near-surface region arising from aggregation and parallel orientation of the bitumen molecules, and the gradient descent configuration in the region further away from the surface. The degree of concentration and radius of influence are significantly impacted by the mineral surface. Distributions of the individual bitumen fractions were also probed for the nearest bitumen layer to test the assumption of selective adsorption. The results suggest that the hypothese of selective adsorption is invalid for bitumen-aggregate interface systems investigated in this paper. The findings from the current study provide molecular insights into the topography of the adsorbed bitumen layer on the aggregate surface.