The sacred mountain of varallo renaissance complex in Italy: Damage analysis of decorated surfaces and structural supports

Acoustic Emission (AE) is a Non-Destructive Inspection Technique, widely used for monitoring of structural condition of different materials like concrete, masonry and rocks. It utilizes the transient elastic waves produced by each fracture occurrence, which are captured by sensors on the external surface. The preservation of the mural painting heritage is a complex problem that requires the use of innovative non-destructive investigation methodologies to assess the integrity of decorated artworks without altering their state of conservation. A complete diagnosis of crack pattern regarding not only the external decorated surface but also the internal support is of great importance due to the criticality of internal defects and damage phenomena, that may suddenly degenerate into irreversible failures. The majority of NDT work by introducing some type of energy into the system to be analysed. On the other hand, in AE tests the input is the mechanical stress inside the material itself during the damage evolution, so that no perturbation is induced and the integrity of the system can be guaranteed. By monitoring the support of a decorated surface by means of the AE technique, it becomes possible to detect the occurrence and evolution of surface vs. support separation and stress-induced cracks. The aim of this study is to reveal by means of the AE technique the damage evolution in the support of the decorated surfaces of the Renaissance Complex “Sacri Monti di Varallo” (Piedmont, Italy) and to utilize the collected data coming from the “in situ” monitoring in order to preserve the artworks from seismic risk and possible collapses due to earthquake actions.