On the investigation of the bulk microstructure of bitumen – Introducing two new techniques

Bitumen, the residue of oil distillation and applied e.g. as binder in asphalt pavements displays a rich microstructure at the bitumen surface-to-air surface with several clearly distinguishable phases. However, uncertainty still remains whether this micro-structure is just present at free surfaces or a similar structure exists in the bulk of the material. Two new experimental techniques in bitumen research (i) one based on Atomic Force Microscopy (AFM) on a freeze–fracture surface and (ii) one technique employing a Scanning Acoustic Microscope (SAM) offer the required spatial resolution and show the presence of two phases in the bulk showing similarities with the known surface structures in bitumen.