Non-destructive 3D measurements of sandstone’s internal micro-architecture using high resolution micro-CT

Abstract

Calcareous stones such as Lecce stones have a high porosity which results in a readily uptake of rainwater. Due to the atmospheric pollutants dissolved in the water these stones, used in a lot of historical buildings, are constantly under attack which leads to a decay of the stone [1]. Different kind of organic hydrophobic products such as Paraloid B72 (PB72) and fluorinated rubber (NH) are often applied as protectives with the aim to reduce the corrosion of the material. In order to study the manner in which these treatment products fill the pores a desktop X-ray microtomography system was used. This technique allows the 3D investigation of the internal structure of the stone in a non-destructive way [2,3]. In this research morphological parameters such as the total porosity (as a percentage of the enclosed empty spaces on the volume of interest), pore size distribution, surface-to-volume ratio (which gives an idea of the complexity of the internal structures) and structure model index (SMI) (giving an estimation of the average shape of the pores (0 = ideal plate, 3 = cylinder and 4 = sphere)) were calculated before and after treatment in order to evaluate the changes induced by the polymer application. The 2D reconstructed cross-sections, shown in Figure 1, confirm that Lecce stone has a very complex internal structure. Several different inclusions such as shells with different shapes and sizes (from a few µm up to 1mm, foraminifera in Figure 1) can be clearly distinguished. The 3D rendering of a small portion of the pores network (Figure 2) gives an idea of the complexity and interconnectivity of the internal structure. The pore size distribution (Figure 2) shows that almost 90% of the pores range from 8 to 29µm.