Study of the Microstructure and Permeability of Building Stone Using X-ray Micro-tomography

Abstract

Fluid transport and storage properties of porous rocks are closely related to their microstructure. Porosity is one of the most important microstructural parameters due to its importance for transport of water, gases and dissolved salts, but also for mechanical, deformation and durability properties of geomaterials used in constructions. In this study, the X-ray computed micro-tomography (XCT) was used to study the spatial distribution of porosity and permeability within the Kocbeře sandstone, which represents a very well-known and long-term used building stone in the territory of the Czech Republic. The microstructure and composition of the Kocbeře sandstone were characterized by a complex of methods, including optical polarization microscopy, scanning electron microscopy coupled with energy dispersive spectroscopy, X-ray powder diffraction, X-ray fluorescence spectroscopy and mercury intrusion porosimetry (MIP). Values of porosity and permeability of the Kocbeře sandstone derived from XCT were compared with results of MIP as well as laboratory measurements of open porosity, hydraulic conductivity and gas permeability. A very good compliance was found between the average values of sandstone porosity determined by the XCT imaging analysis, MIP and experimentally determined open porosity. However, considerable heterogeneity of porosity in the individual analyzed subvolumes was detected using XCT. Very significant inhomogeneity was also found in the spatial distribution of permeability tensors calculated for individual subvolumes. The considerable dispersion of porosity and permeability values of sandstone at the microscale is given by its microstructure. The main role here is played by intense secondary silicification, which unevenly affects the clay matrix of the sandstone.