Monitoraggio del degrado e conservazione del Patrimonio monumentale della Regione Sardegna attraverso caratterizzazione geochimica, petrofisica e micro-fotogrammetrica di superfici lapidee

Cultural Heritage of Sardinia (Italy) consists of a large number of historical monuments belonging to different cultures (e.g. Nuragic, Roman, Phoenician-Punic, Romanesque, Aragonese), from 1800 BC to 1700 AD. Some of these buildings, nowadays in a poor state of conservation, are subject to management and monitoring plans. In this research, four representative archaeological sites from Roman to Romanesque cultures are the topic of an in-depth study. The project focuses on ancient mortars, stones and paintings. An integrated and multi-scale approach proposed in this project, combines classical physical-mechanical, petrographic and geochemical investigations (archaeometry) with accelerate aging tests (AAT). Optical mineralogy observations (OM) on stones permit the rock classification and the identification of ancient supply quarries. In the case of marbles, the provenience of the rocks was established by cross-analysis OM and isotope-ratio 13C vs 18O. OM on mortars identifies the environment origin and typology of aggregates. Both mortars and stones are subject to physical-mechanical tests in order to obtain densities, porosities, imbibition and saturation indices, tensile and compressive strengths. In addition, the particle-size distribution (PSD) of mortar aggregates points out information about the production methodology. A XRPD diffraction associated with SEM-EDS and TGA-DSC analysis on mortar binders recognized alteration mineral phases and established the hydraulicity degree. In addition μXRD with associated μRaman spectroscopy and μFT-IR have been carried out on the fresco to characterize the pigments and their binder. By in-situ observations and digital image reconstruction, decay mapping of some building portion highlight the diverse alteration forms of the stone. Accelerated aging tests on samples with analogue lithology to the one used in the selected monument, try to reproduce these alteration forms in laboratory. The aging tests, conducted by climatic chambers, faithfully reproduce the temperature, humidity, capillary rising, CO2 air content and solar radiation of the environment context where the monuments are located. All macroscopic morphologic modifications have been represented before and after the aging tests by 3D photogrammetric modelling (online available). Furthermore, before, after and in some case during the aging tests, a wide series of physical-mechanical parameters (e.g. linear roughness, mass, color changes, mechanical strengths, densities, P ultrasonic speeds.) and chemical parameters (e.g. efflorescences characterization) have been evaluated. Traditional applied petrography approach allows to observe the actual decay state and accelerated aging tests predict the modalities of decay development in the future.