Molecular investigation on the adhesion and deformation behaviors of asphalt binder under nanoindentation

Abstract

The adhesion of asphalt binders at micro/nano-scale remains one of the least understood and explored areas of the constitutive characteristic of asphaltic composites. In this study, the displacement-controlled nanoindentations were performed using a rigid, conical quartz indenter on the asphalt binder substrate by molecular dynamics (MD) simulation. To accurately describe the mechanical response of asphalt substrate, a reasonable force-displacement (f-d) curve was depicted via determining the initial contact point. Meanwhile, the deformation response of asphalt substrate can be intuitively analyzed from the atomic strain and displacement of the asphalt substrate. Significant curvilinear motion and isotropic plastic deformation in asphalt substrate were observed. The adhesion forces between indenter and asphalt substrate under different indentation depths were also investigated. An adhesion strength model was established. From this model, the size effect was clearly observed, which shows that the adhesion strength reaches a peak value and then gradually declines with an increase of indentation depth. The laboratory nanoindentation test on asphalt binders indicated that the calculated adhesion force is in good agreement with that from the measurement. Moreover, the influence of surface contamination was further investigated. It is shown that the capillary force and interaction from the contamination layer contribute to the rise of adhesion force. The present study raises the practicability of using MD to explore the nanoindentation processes and assists in elucidating the basic adhesion mechanisms involved.