X-ray CT: a powerful technique for the micro-structural analysis of geomaterials.

For the 3D characterisation on a (sub)micron scale of the pore structure of natural stones as well as for the study of their weathering processes, both 3D structural and chemical composition and distribution of pores and minerals are important. These characteristics can be obtained through traditional research techniques (including optical microscopy, SEM, laboratory experiments, etc.) and through highly advanced techniques like highresolution X-ray CT; after acquisition, the fusion of all this data can provide a better insight in the weathering phenomena occurring in geomaterials. At the Sedimentary Geology and Engineering Geology group of UGent, X-ray CT technology is applied in the study of geomaterials and is one of the group‟s main research topics for already more than 15 years. The group acted as co-founder of the „Centre for X-ray Tomography‟ (UGCT, UGent), of which the developed flexible highresolution X-ray CT (HRXCT) scanners and software tools are being used for the 3D characterization of geomaterials, for fluid-flow monitoring inside porous materials and for the study of weathering phenomena of geomaterials. For geologists, who normally work with optical microscopy and scanning electron microscopy to study geomaterials, CT offers an important research tool since it allows to provide information on the 3D structure of the scanned samples as well as limited information on their chemical composition in a non-destructive way. Scanned samples can afterwards always be analyzed by the more traditional research techniques, like optical microscopy and scanning electron microscopy combined with EDX (SEM-EDX), in order to connect the 3D data from the X-ray scanners with the 2D chemical and structural information from microscopy techniques. Additionally, thanks to close collaboration with the research group „X-ray microspectroscopy and imaging‟ (headed by Prof. Laszlo Vincze, Ghent University), XRF imaging at a micro- and nanoscale level is integrated in the 3D study of geomaterials and their weathering phenomena. Previous experiments (Cnudde et al., 2009; Boone et al, in press) convincingly demonstrated the added value of the link between both techniques for the characterization and understanding of the behaviour of geomaterials submitted to changing external conditions. The use of two powerful and complementary “state-of-the-art” techniques combined with information obtained from optical microscopy and SEM-EDX, traditionally used for characterisation, allows to determine and assess structural information and chemical element distributions in 3D in geomaterials and this with a spatial resolution better than 1 micrometer. In this extended