Analysis of subsurface water content with integrated techniques

A study of the problem of deterioration of a historical monument, the Crypt of the "Cattedrale di Otranto” (Lecce, South Italy), integrating different non destructive techniques (microclimatic and Ground Penetrating Radar) is proposed. In literature the degradation of stone is attributed to the presence of water and/or moisture in the porous material that occurs in water-damaged and humid buildings, due to poorly manufactured constructions and inadequate maintenance. The distribution of moisture within stone mainly depends on unsuitable environmental conditions and the presence of wet buried structures in the ground. After microclimatic surveys, through which we assessed unsuitable condition in the Crypt, Ground Penetrating radar (GPR) surveys were carried out. A careful analysis of the 0.4 m spaced GPR parallel profiles, acquired in the Crypt using a Sir2 GSSI radar system with a 500 MHz antenna, allow us to distinguish the wet and the moisture zone. GPR data was displayed in time slices form to obtain both the amplitude and the moisture variations map. Moreover GPR data was displayed in the form of frequency slices to highlight absorption losses probably related to higher moisture content. Therefore the GPR data was compared with the microclimatic data, and a good agreement was found, suggesting that an important channelling of moisture has its origin in the subsoil