Nanostructure characterization of asphalt-aggregate interface through molecular dynamics simulation and atomic force microscopy

Abstract

Although it has been widely accepted that the asphalt-aggregate interface plays as one of the most important roles for the durability of asphalt concrete, it is still a big challenge to elucidate the failure mechanisms when it is exposed to moisture environment due to the lack of sufficient information on the nanostructure of the asphalt-aggregate interfaces. To understand the failure mechanisms of the asphalt concrete resulted from the moisture damage, the Molecular Dynamic (MD) simulation and the PeakForce Quantitative Nanomechanics atomic force microscopy (PFQN-AFM) were used to characterize the nanostructure of the asphalt-aggregate interface. The MD simulation results demonstrated that, at the asphalt-aggregate interface, the nanostructure is constructed by periodical molecular bulgy boundaries and central cavities. The polar aromatics not only form the structural skeleton with the asphaltenes aggregations, but also act as the stabilizer to enhance the compatibility between asphaltenes and maltenes. Besides, it was found that the intermolecular gaps can be filled by naphthene aromatics, and molecular micelles can be lubricated by saturates. The AFM results show that, some regions in the asphalt-aggregate interface have lower adhesion force with the tip than the surrounding regions. The low adhesion regions are relevant to the structure that polar molecules aggregate into boundaries and evade the center. The dissolution of polar molecular into water induces the nanostructure collapse, and further leads to the asphalt-aggregate interface debonding. This study not only presents the nanostructure of the asphalt-aggregates interfaces, but also helps to understand the moisture damage mechanisms of the asphalt concrete.