Complex Pore Geometries in Natural Building Stones: an experimental and theoretical approach for the modeling of porosity changes in natural, degraded and treated calcarenites

Abstract

Calcarenites are the most widely used natural stones in Sicily as building materials. The comprehension of the degradation style of these natural building stone is of great interest in order to preserve the ancient masonry, especially in the case of relevant Cultural Heritages. A large number of Sicilian monuments are included in UNESCO Heritage List as their special cultural or physical significance. Considering the cultural importance of these ones, smart solutions are required in the perspective of their conservation. In the framework of restoration actions, the complete knowledge of the internal structure of building stones is fundamental in order to estimate durability and prevent degradation processes. Salt growth is a significant cause of damage for natural stones. The effects of the salt weathering are, in addition to the properties of the salt itself and the climatic conditions, strongly related to the structural and textural features of materials. For this reason, an integrate study on petrographic, physical, mechanical and porosimetric proprieties changes due to salts crystallization could be useful to highlight correlation among textural, structural and engineering parameters. Moreover, one of the main problems in conservation field is the use of suitable consolidant and protective treatments able to preserve the masonry, being compatible with the stone substrate and not affecting its aesthetical proprieties. There are numerous tests able to verify the efficiency of consolidant or protective products, mainly devoted to verify their ability to not modify the appearance of stone and its physical proprieties, especially against water; however, particularly in the case of consolidant, one of the most important feature is related to its penetration depth, often difficult to evaluate by using the standard test routines. For aforementioned, this research work is devoted to apply a multi-methodological approach for characterizing and modeling pore structure modifications due to weathering processes in a coarse grained Sicilian calcarenite used as building and replace stones in Sicilian Cultural Heritages (Sabucina Stone), also through fractal models and innovative and non invasive methods. The obtained data on Sabucina stone have been employed for planning conservative treatments devoted to coarse grained calcarenite substrates. Therefore, innovative nanostructured and hybrid consolidant and protective products have been experimented and the results of efficiency tests along with the determination of surface and sub-surface changes due to the treatments are proposed. In conclusion, the applied theoretical and empirical approach has allowed to: highlight the potential of classical and innovative complementary methods in quantifying the structural changes in porous materials due to degradation processes and conservative treatments, explain how they help to facilitate the understanding of stone weathering and validate the use of geometrical models in describing complex pore systems.