Autogenous healing of cracks may offer a solution for brittle cementitious materials. In this study, the healing building blocks are available through the well-designed ultra-ductile microfibre-reinforced mixture with a low water-to-binder ratio and water is available through the inclusion of superabsorbent polymers. As visual inspection demonstrates that the crack is completely closed at the surface, one may ask whether this healing also is present in the interior of the crack. X-ray computed microtomography was therefore used to study the extent of autogenous healing in cracked cylindrical specimens. It was found that the extent of autogenous healing in a cementitious material depends on the crack depth. Only near the crack mouth (0 till 800e1000 mm) the crack is closed by calcium carbonate formation in case of wet/dry cycles. In combination with superabsorbent polymers, the extent of healing was more substantial. For mixtures containing superabsorbent polymers there was even partial healing in the interior of the crack when stored at a relative humidity of 60% or more than 90%. Energy-dispersive spectroscopy combined with microscopic analysis showed that the healing products were mainly calcium carbonate. The smart cementitious material with superabsorbent polymers is thus an excellent material to use in future building applications as the healing capacity is improved.

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Three-dimensional (3D) analysis is an essential tool to obtain quantitative results from 3D datasets. Considerable progress has been made in 3D imaging techniques, resulting in a growing need for more flexible, complete analysis packages containing advanced algorithms. At the Centre for X-ray Tomography of the Ghent University (UGCT), research is being done on the improvement of both hardware and software for high-resolution X-ray computed tomography (CT). UGCT collaborates with research groups from different disciplines, each having specific needs. To meet these requirements the analysis software package, Morpho+, was developed in-house. Morpho+ contains an extensive set of high-performance 3D operations to obtain object segmentation, separation, and parameterization (orientation, maximum opening, equivalent diameter, sphericity, connectivity, etc.), or to extract a 3D geometrical representation (surface mesh or skeleton) for further modeling. These algorithms have a relatively short processing time when analyzing large datasets. Additionally, Morpho+ is equipped with an interactive and intuitive user interface in which the results are visualized. The package allows scientists from various fields to obtain the necessary quantitative results when applying high-resolution X-ray CT as a research tool to the nondestructive investigation of the microstructure of materials.

Weathering processes have been studied in detail for many natural building stones. The most commonly used analytical techniques in these studies are thin-section petrography, SEM, XRD and XRF. Most of these techniques are valuable for chemical and mineralogical analysis of the weathering patterns. However, to obtain crucial quantitative information on structural evolutions like porosity changes and growth of weathering crusts in function of time, non-destructive techniques become necessary. In this study, a Belgian historical calcareous sandstone, the Lede stone, was exposed to gaseous SO(2) under wet surface conditions according to the European Standard NBN EN 13919 (2003). Before, during and after the strong acid test, high resolution X-ray tomography has been performed to visualize gypsum crust formation to yield a better insight into the effects of gaseous SO(2) on the pore modification in 3D. The tomographic scans were taken at the Centre for X-ray Tomography at Ghent University (UGCT). With the aid of image analysis, partial porosity changes were calculated in different stadia of the process. Increasing porosity has been observed visually and quantitatively below the new superficial formed layer of gypsum crystals. In some cases micro-cracks and dissolution zones were detected on the grain boundaries of quartz. By using Morpho+, an in-house developed image analysis program, radial porosity, partial porosity, ratio of open and closed porosity and equivalent diameter of individual pore structures have been calculated. The results obtained in this study are promising for a better understanding of gypsum weathering mechanisms, porosity changes and patterns on natural building stones in four dimensions.

Authigenic gypsum was found in a gravity core, retrieved from the top of Mound Perseverance, a giant cold-water coral mound in the Porcupine Basin, off Ireland. The occurrence of gypsum in such an environment is intriguing, because gypsum, a classic evaporitic mineral, is undersaturated with respect to sea water. Sedimentological, petrographic and isotopic evidence point to diagenetic formation of the gypsum, tied to oxidation of sedimentary sulphide minerals (i.e. pyrite). This oxidation is attributed to a phase of increased bottom currents which caused erosion and enhanced inflow of oxidizing fluids into the mound sediments. The oxidation of pyrite produced acidity, causing carbonate dissolution and subsequently leading to pore-water oversaturation with respect to gypsum and dolomite. Calculations based on the isotopic compositions of gypsum and pyrite reveal that between 21·6% and 28·6% of the sulphate incorporated into the gypsum derived from pyrite oxidation. The dissolution of carbonate increased the porosity in the affected sediment layer but promoted lithification of the sediments at the sediment-water interface. Thus, authigenic gypsum can serve as a signature for diagenetic oxidation events in carbonate-rich sediments. These observations demonstrate that fluid flow, steered by environmental factors, has an important effect on the diagenesis of coral mounds