Bohemian sandstone for restoration of cultural heritage sites: 3D microstructure and mass transport properties

We characterised the microstructure of sandstone from the Msene locality (Czech Republic) by combining X-ray computed micro-tomography, back-scattered electron imaging, chemical composition analysis and textural analysis and gas permeation. Both, 2D and 3D images were commonly processed by linking an anisotropic non-linear diffusion filter and a segmentation method based on power watershed. This approach guaranteed binarised outputs that were almost the same in wide ranges of spatial-filter and power-watershed parameters, i.e., subjective choices of the parameters played the negligible role. The rock pore structure was found to be statistically homogeneous and almost isotropic with perfectly connected pore space. We also partitioned the void and solid phases into either grains or pores and throats, which enabled us to study characteristic sizes and connectivity of partitioned regions. By comparing pore and throat sizes, we demonstrated the significant convergent-divergent nature of the pore space because the throat size covered at most one half of the total surface area per pore (cavity). In addition, we calculated coordination numbers for all pores (cavities) to verify almost perfect connectivity of internal pores with those at the external surface. Effective (macroscopic) transport properties of the reconstructed pore space were simulated and the results were validated by experimentally observing steady state flow of inert gas. These findings appear to be a favorable starting point for future investigation of consolidation procedures. The well-connected pore structure with minimum occurrence of dead-end pores suggests that the consolidation agent is very likely to flood the whole pore space.