Study of asphalt binder diffusion using atomic force microscopy

During asphalt recycling process, diffusion of asphalt binder takes place between the aged binder adhered to the RAP aggregates and the virgin binder. Complete mixing between the two binders may not necessarily happen during the recycling process. Study of diffusion is, therefore, an important consideration in asphalt recycling. Researchers have experimentally studied the phenomenon of diffusion typically by using Dynamic Shear Rheometer (DSR) or Fourier Transform Infrared Spectroscopy (FTIR). In the present work, possibility of using Atomic Force Microscopy (AFM) to study binder diffusion is explored. In this study, two different binders is used in a circular geometry, so as to closely resemble an aggregate (from RAP) surrounded by a pool of virgin binder. AFM images are taken along the radial direction of the sample to study the progression of diffusion at different locations. The relative concentration of binders at these locations are estimated from the AFM images. From the present study, based on limited data, it appears that AFM can be used for studying diffusion between asphalt binders.