Analysis of Adhesive Characteristics of Asphalt Based on Atomic Force Microscopy and Molecular Dynamics Simulation

TLDR

Adhesive bonds between asphalt binder and mineral aggregate are critical for asphalt concrete performance, yet most proposed mechanisms remain unconfirmed, with physical adsorption considered the dominant interaction. The study investigates the adhesive characteristics of asphalt binder on silicate minerals by employing atomic force microscopy and molecular dynamics simulations. A silicon tip represents silicate minerals, and nanoscale adhesion is examined through AFM measurements and MD simulations of asphalt–silicon interactions. Results show that high‑density planar asphaltene molecules enhance adhesion, the colloidal structure of asphalt significantly affects bonding, and a schematic model explains aging‑induced changes, thereby improving understanding of bonding and debonding during hot mixing and traffic loading.

Abstract

Asphalt binder is a very important building material in infrastructure construction; it is commonly mixed with mineral aggregate and used to produce asphalt concrete. Owing to the large differences in physical and chemical properties between asphalt and aggregate, adhesive bonds play an important role in determining the performance of asphalt concrete. Although many types of adhesive bonding mechanisms have been proposed to explain the interaction forces between asphalt binder and mineral aggregate, few have been confirmed and characterized. In comparison with chemical interactions, physical adsorption has been considered to play a more important role in adhesive bonding between asphalt and mineral aggregate. In this study, the silicon tip of an atomic force microscope was used to represent silicate minerals in aggregate, and a nanoscale analysis of the characteristics of adhesive bonding between asphalt binder and the silicon tip was conducted via an atomic force microscopy (AFM) test and molecular dynamics (MD) simulations. The results of the measurements and simulations could help in better understanding of the bonding and debonding procedures in asphalt–aggregate mixtures during hot mixing and under traffic loading. MD simulations on a single molecule of a component of asphalt and monocrystalline silicon demonstrate that molecules with a higher atomic density and planar structure, such as three types of asphaltene molecules, can provide greater adhesive strength. However, regarding the real components of asphalt binder, both the MD simulations and AFM test indicate that the colloidal structural behavior of asphalt also has a large influence on the adhesion behavior between asphalt and silicon. A schematic model of the interaction between asphalt and silicon is presented, which can explain the effect of aging on the adhesion behavior of asphalt.