Fundamental Characterization of Asphalt Clay Nanocomposites

Abstract

This study aims at characterizing the nanostructure and microstructure and the mechanical behavior of asphalt clay nanocomposites. To this end, various atomic force microscopy (AFM) techniques (i.e., tapping mode imaging, force spectroscopy, and nanoindentation) and X-ray diffraction (XRD) experiments were conducted on asphalt binders modified with different contents of a nanoclay material. The AFM images and XRD results indicated that the nanoclay had an exfoliated structure within the nanocomposite. In addition, the AFM images showed better interaction between the nanoclay layers and the distinct asphalt domains containing the so-called “beelike” structures as compared to the flat asphalt matrix. The results of the force spectroscopy experiments indicated that the inclusion of the nanoclay material significantly enhanced the adhesive forces of asphalt materials, while it had a slightly adverse effect on the cohesive forces. Furthermore, the nanoclay material improved the stiffness and hardness of the asphalt binder measured in the indentation tests. However, this enhancement was affected by the temperature and nanoclay percentage. The results of this study suggest that the mechanical behavior of the asphalt clay nanocomposite can be explained by the formation of a rigid percolating network consisting of the exfoliated nanoclay layers and the fractal asphaltene aggregates in the asphalt binder. The onset of the rigidity percolation appears to be dependent on the effective radius of the asphaltene aggregates and the spacing between the nanoclay layers, a conclusion that may require further experimentation to validate.