Cristallizzazione del solfato di sodio in calcari biomicritici: l'uso di inibitori per la mitigazione del degrado

Salt crystallisation is one of the most harmful decay problems in porous materials. Especially ancient building and archaeological sites can show very intense damage (e.g. detachment and pulverization of the materials) that produce a strong loss of matter and so cultural identity. Mainly hypogea show salt crystallisation due to capillary rising. However also anthropic sources like pollution or cement can be found in these sites producing decay. Sodium sulphate is very common where there is the combination between cement and pollution. This salt is very harmful for porous materials due to his high crystallization pressure and the possibility to change to anhydrous phase to hydrated one. When microclimatic variations occur due to semi-confined environment, phase transitions of sodium sulphate take place with consequence on porous material decay. This research studied sodium sulphate crystallisation on a Mediterranean biomicritic limestone and the action of crystallisation inhibitors to mitigate it. The early Christian burial of Munazio Ireneo was studied to understand sodium sulphate crystallisation in biomicritic limestone. Diagnostic investigation and microclimatic monitoring were carried out to understand decay phenomena. The hypogeum is a semi-confined environment and high damage can be found due to phase transition of sodium sulphate. Crystallisation of a Mediterranean biomicric limestone was also studied in laboratory by XRD, OM, SEM, MIP and NMR analysis. Crystallisation inhibitors were tested on the limestone in sodium sulphate solution capillary rising. Two different inhibitors were applied with two distinct system (immersion and poultice). XRD, MIP and SEM analysis were carried out to understand the modification of the inhibitor on the stone microstructure. The loss of material was evaluated to understand the effect of the inhibitors comparing the loss of material in the blank sample. A greater loss of material than the blank sample was found when the first inhibitor was applied through both of the system; the second inhibitor had a minor loss of material but chromatic variations could be found on the stone.