Microclimatic and Ground-Penetrating Radar surveys for damage diagnosis. The case of the Crypt of the Duomo of Lecce (Italy)

The presence of particular microclimatic conditions inside monumental buildings is responsible for deterioration processes. In many cases, efflorescences and moulds are visible on the façade or the interior of several monuments of historical importance. In other cases, the effects of decay processes are not visible. So, the diagnosis and the consequent set up of effective interventions for conservation are difficult, especially in presence of complex geometry and large variability of construction materials. The Duomo and its Crypt is one of the most important buildings in the city centre of Lecce (South-Italy). Especially in the Crypt, salt damage is evident, enhanced by the hypogeum position and incorrect interventions too. In order to identify the conditions that favour crystal growth, we performed both a microclimatic monitoring and a sub-surface investigation and characterization, by using Ground-Penetrating Radar (GPR)technique. The microclimatic conditions that allow the salt variations over time are given. The spatial variation in GPR signal attenuation permits us to assess the physical and hydrological nature of the pore fluids and associated damages. The analysis of that data in form of “frequency maps” highlights absorption losses, probably linked to high moisture content. Moreover, stratigraphically complex layers of archaeological remains under the Crypt were revealed.