The use of CT analysis in revealing structural heterogeneity of freshwater carbonate decoration and construction stones

Abstract

This article presents the findings of a CT analysis conducted on freshwater carbonate rocks found in the Danube-Tisza Interfluve. These rocks are utilized for both construction and decoration purposes in the medieval buildings of the region. The aim of the study was to uncover some petrophysical properties of the rocks deriving from the Csólyospálos quarry. The proportions of the main constituents of the rocks carry significant information about the formation and alteration history of sedimentary rocks. To comprehend and assess the nature of these processes, as well as the resulting spatial variations, it is necessary to gather quantitative data on the distribution of these constituents at both macro- and microscales. The researchers employed an EMmixture analysis that considered the density differences among the individual constituents to determine the quantitative characteristics of the main components that form the rocks. By setting a threshold value to distinguish macropores (empty spaces) with lower density values from the solid matrix, the percentage of voids was calculated for each CT slice. The distribution of these voids was examined in three dimensions along all possible axial directions (X, Y, Z). Watershed algorithm, and Laplace operator were applying on selected CT slices that corresponded to areas with similar compositional features. This approach helped identify potential flow directions within the rocks. The spatial distribution and orientation of macropores, which could be visualized using CT at a resolution of over 200 microns, provided valuable insights into the paths through which water could enter the carbonate rocks used for construction or decoration. This information is crucial in understanding structural damage caused by frost weathering and dissolution via capillary action once a staticstate flow is established. Furthermore, these findings complement the results obtained from laboratory geotechnical measurements.