Morphology of asphalts, asphalt fractions and model wax-doped asphalts studied by atomic force microscopy

Asphalts used in the construction of pavements exhibit unique properties at the micron and nanometre scale. Atomic force microscopy (AFM) images of asphalts and asphalt chromatographic fractions prepared as thin films clearly show that a variety of 'microstructures' can develop on the surface of these types of materials. Structure develops to different degrees and in different forms depending on the residua crude source from which the asphalt or asphalt fraction is derived, the thermal history of the sample and the sample thickness. Based on our current best interpretation of a very large number of AFM images obtained over several years, we hypothesise that the interaction between crystallising paraffin waxes and the remaining asphalt fractions is responsible for much of the structuring, including the well-known bee structures (Loeber et al. 1996, Journal of Microscopy, 182 (1), 32-39), which has been observed with asphalt materials.