Microscale morphology observation of bitumen: A comparison of atomic force and confocal laser scanning microscopy

Abstract

Bituminous binders can display a rich microscale morphology, including so-called bee structures. In literature, not only bees but several phases have been identified on bituminous surfaces. Currently, atomic force microscopy (AFM) is the most popular technique to investigate these microstructures. In AFM a near or direct contact between the tip and the bitumen surface forms the basis for a measurement, and accordingly, there are also some restrictions: AFM tapping mode is only possible when the tackiness of the specimens is low enough, or viscosity sufficiently high. At steep walls or overhangs, artefacts may develop when testing these with AFM. And in tapping mode, accidental collisions between the vibrating cantilever nanotip and the sample can occur. To overcome these limitations, the use of a confocal laser scanning microscope (CLSM) is proposed. The paper aims at exploring the possibilities of a confocal laser scanning microscope as a complementary technique to AFM, and to solve some of the limitations observed when using AFM tapping mode.