Characterisation of ‘Hadley’ grains by confocal microscopy

This work forms part of an exploratory study to investigate the use of fluorescent laser scanning confocal microscopy (LSCM) for imaging pores and voids in hardened mortar and concrete. The study has revealed the suitability of the technique for the characterisation of hollow shell (Hadley) hydration grains (these are grains that contain a void within the original boundary of the cement grain). It was found that Hadley grains could be imaged using fluorescent light techniques, subsequent to their impregnation by epoxy resin doped with a fluorescent dye. Prior to this work, it was not clear whether hollow grains were impregnated due to connections with capillary pores, or if they had been impregnated due to connections with damage caused during surface preparation (i.e. micro-cracks or deep surface scratches). However using the 3D LSCM imaging technique it was observed that connections between Hadley grains and hardened cement paste (HCP) capillary pores did exist, in different forms, at depths well below the surface providing ‘conduits’ along which resin was able to flow and impregnate the hollow grains. Other aspects of imaging Hadley grains are also described, such as the sectioning of ‘tips’ of larger grains often taken as separate smaller pores or grains in 2D images.