Mara Camaiti

Investigating morphological changes in treated vs. untreated stone building materials by x-ray micro-CT

AbstractCalcareous stones have been largely used to build historical buildings. Among these, the calcarenites are usually characterized by a high content of calcite and a high open porosity, which make them very sensitive to the weathering caused by physical and chemical agents. In order to prevent their deterioration and to retard their decay, different protective products—mainly polymers—are applied on the stone artefact surfaces. In this work we apply the methodology tested in a preliminary study to investigate the morphological changes of the internal structure of a biocalcarenite (Lecce stone) by micro x-ray computed tomography (μ-CT). The porosity and other morphological parameters of the rock before and after the conservation treatment were calculated on a significant number of samples. The Student’s t test was applied for statistical comparison. The results reveal that the treatment with Paraloid B72 (PB 72) is homogenously distributed and causes small changes to the natural properties of the rock, whereas the application of a fluoroelastomer (NH) causes an appreciable decrease in porosity and variation in terms of wall thickness distribution, probably resulting from its inhomogeneous distribution.n FigurePorosity and other morphological parameters of Lecce stone were investigated by μ-CT: the effect of conservation treatment with fluoroelastomer on wall thickness distribution is illustrated

Hyperspectral Sensors for the Characterization of Cultural Heritage Surfaces

The characterization of artistic and historical surfaces in a wide, fast, low-expense, and noninvasive way is a necessity for the conservation of these cultural assets. Hyperspectral sensors having bands in the visible-near infrared and short-wave infrared (VNIR-SWIR) regions are commonly used for determining the characteristics and properties of many materials (such as soils, minerals, rocks, water, vegetation) because of their ability to provide information in a fast and nondestructive way. Among the existing VNIR-SWIR techniques, field spectroscopy and imaging spectroscopy (remote sensing) have a crucial part in the characterization of different kinds of surfaces. In this work, the potentialities of hyperspectral sensors (working in the range 0.35–2.5 μm) for cultural heritage applications are discussed. The attention is focused both on field spectroscopy as a method for accurate characterization of small, confined, and highly heterogeneous surfaces and on imaging spectrometry obtained through field sensors. A few case studies where both techniques were employed are also reported.

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

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.