Imaging ed analisi 3D della struttura porosa del Tufo Giallo Napoletano: un contributo allo studio del degrado dei materiali a Castel Nuovo

Façades of Castel Nuovo made with bricks of Tufo Giallo Napoletano (TNG) show, among other types of stone decay, a certain extent of black crusts. Such a kind of degradation can be due to pollution from vehicular and marine traffic or microorganisms or both. In any case an analysis of how and how much such crusts penetrate under the surface of the bricks must take into account the porous structure of the above mentioned rock material. Multiscale scannings of samples of TGN from the southern façade of the castle has been carried out by means of X-ray microCT in order to reconstruct images of its natural and degraded inner structure. The 3D image analysis algorithm of "successive opening" has then been applied to determine the size distribution of both isolated and outer connected pores of the TGN. The crust thickness and its distribution inside the pores on the surface of the rock material has also been evaluated. Results allowed to quantify the relationship between the porosity of the outer connected pores and the thickness of the layer where the crusts penetrate inside the TGN. Quantification of the outer connected pore volume can also provide useful information to address the restoration treatmens.