Consolidamento di supporti lapidei carbonatici caratterizzanti i Beni Culturali attraverso formulati inorganici mineralizzanti: applicazione ed efficacia.

Although the extensive use of carbonate rocks in architecture and sculpture go up since ancient times, such rocks are subjected to high vulnerability when submitted to the action of decay agents. The exposure to weathering and anthropic actions are capable of microstructural variations in load resistance and durability of the rocks, producing a quantitative loss and qualitative modifications of the employed materials, which compromise the durability and the aspect of the cultural heritage. Consolidation is one of the key issues as concerns the conservation of Cultural Heritage, and is often the practice required to ensure the preservation of the artifacts. From scientific literature emerges the lack of resolution of some issues associated to the restoration and conservation of materials: i) real effectiveness of the treatments employed in the restoration for the surfaces cohesion, very important to ensure durability; ii) the achievement of adequate penetration depth of the newly-formed mineral phases; iii) compatibility with the stone substrates; iv) absence or reduction of unexpected derived effects; v) control of nucleation and growth of newly-formed phases. The present work fits the open issues and, through a systematic experimentation, is aimed to suggest some solutions as concerns the main tasks above-mentioned. The experimental materials were selected between two different carbonatic lithotypes, due to their widespread use in the Mediterranean area. The rocks come from two Italian quarries: a Carrara marble facies (Marmo Statuario Michelangelo, Apuan Alps) and a limestone facies (Santa Caterina di Pittinuri) were collected from Tuscany and central Sardinia, respectively. To simulate the in situ degradation, an accelerated aging method was adopted, operating by thermal stress processes at elevated temperatures, to cause microstructural decay. Two unmarketable inorganic products were employed to cause an induced mineralization of newly-formed mineral phases, compatible with the stone substrates: i) the diammonium hydrogen phosphate (DAHP), recently proposed from some Authors to promote the formation of calcium phosphates, mainly hydroxyapatite (HAP); ii) an innovative inorganic salt ammonium methyloxalate (AmMeox), as an unconventional precursor of calcium oxalate phases (CaOx) . Furthermore, the role of several analytical techniques was investigated, to define the most suitable ones for the objectives of the present work. At this purpose, the operating parameters such as time, temperature, concentration of the solutions, were checked. To characterize the untreated selected materials as well as to evaluate the effectiveness of the treatments after the application of the consolidants to the thermal stressed stones, a multi-analytical approach was established by the application the following different analytical techniques and laboratory tests: i) Optical Microscopy, in polarized light (OM), ii) Fluorescence Microscopy (FM), iii) X-Ray Diffraction (XRD), iv) Raman Spectroscopy, v) Computed Tomography (CT), vi) Scanning Electron Microscopy (SEM), vii) Energy Dispersive X-Ray Spectrometry (EDS), viii) Mercury Intrusion Porosimetry (MIP), ix) measurement of the ultrasonic propagation speed, x) spectrophotometry, xi) roughness, xii) hardness, xiii) static angle contact, xiv) hydric behavior. (key words: marble, limestone, stone decay, inorganic consolidants, coatings, role of procedures, thermal stress)