Applicazione di tecniche diagnostiche non distruttive per la caratterizzazione dei materiali costruttivi di natura carbonatica

The geological district of Cagliari and the Maltese archipelago are composed mainly of limestones, the most important of which are the Oligo-Miocenic Limestone of Cagliari and the Globigerina Limestone, which are widely used in construction. The Oligo-Miocenic limestone of Cagliari is commonly known to exist as three main types: “Pietra Forte”, “Tramezzario” and “Pietra Cantone”. The Globigerina Limestone is commonly known to exist as two main types: "Franka" and "Soll", which terms derive from the terminology used by quarry and construction workers. Currently many buildings of Cagliari and Maltese buildings are still being built using limestone; in addition all the important historical buildings in Cagliari and in Malta are also constructed in this material, among these the most important Maltese monuments belong to UNESCO World Heritage. The Oligo-Miocenic limestone of Cagliari and the Globigerina Limestone (as the type "Soll" of Globigerina Limestone), manifest problems of durability and weathering resistance, especially due to the presence of soluble salts. Thus the ability to distinguish the types of limestone before extraction from the quarry and its use in construction and restoration is of prime importance. As regards the Globigerina Limestone, for hundreds of years in Malta the selection of this limestone has been entrusted to quarry and construction workers, who with their experience and using primarily visual and tactile criteria, can usually identify a suitable material for construction and distinguish between types, something which is impossible for a person not experienced in this field. The current work provides an example of how it is possible to distinguish between the different types of Oligo-Miocenic limestone of Cagliari and Globigerina Limestone, at least those at the "extremes" of the range of types, and their water absorption characteristics (fundamental when durability is being considered), using non-destructive analytical methods - ultrasonic and thermographic methods - in a novel way for this specific material. These methods should offer an additional option to the macroscopic identification of these materials and conventional laboratory tests. It is also useful to distinguish the type and quality of the limestone used in an existing construction in order to perform a diagnosis of the state of conservation of the work and to be able to perform, more consciously, an eventual intervention of restoration. In this perspective, in this work, taking into account the interesting results obtained in the experiments carried out in laboratory, are also presented the results of in situ experiments, carried out on monumental and modern structures. The on-site analysis were performed using the same techniques used for laboratory measurements -ultrasonic and infrared measures-, these non-destructive techniques are used to perform speditive and reliable analysis and allow to operate without causing damage to the structures.