X-Ray Computed Tomography as a Non-Destructive Tool for Stone Conservation

Lecce stone is a biocalcarenite with a very high content of calcite. It has been used for long-time for the historical building in the south of Italy, especially during the Baroque period, but it is also used in the modern time. As a consequence of its high porosity (typically 40% accessible to water), it can readily take up (rain)water that can facilitate the corrosion of the rock due to the action of acidic pollution gases, such as SOx and NOx. Different kinds of organic products (Paraloid B72, fluorinated rubber or solutions of alkylalkoxysilanes oligomers) are normally applied as hydrophobic coatings (protective agents) with the aim to reduce the damage of the material. In order to examine thoroughly the distribution of the protectives and the changes of the stone porosity due to these treatments, a number of magnified X-ray computed tomography measurements were performed, using both laboratory instruments and Synchrotron radiation at the beamline ID19 of ESRF. The product distribution was evaluated by porosity and other morphological parameter measurements: the results reveal that the porosity can be determined with high reproducibility and that there are significant changes of the total porosity and pores size distribution occurring as a consequence of the treatments.