13th International Conference on Fracture June 16–21, 2013, Beijing, China -3- Fig.3. Chapel XXXIII. Ecce Homo. Fig.4. Chapel XVII. The Transfiguration of Christ on Mount Tabor. 2. Chapel XVII monitoring set-up The Acoustic Emission monitoring is conducted on the frescoed masonry walls of the Chapel XVII of the Sacred Mountain of Varallo: the Chapel of the Transfiguration of Christ on Mount Tabor (Fig.4). The construction of the Chapel XVII began in 1572, but the structure was completed only in 1647. In 1664 was built the lantern top as crowning. The purpose of monitoring by means of AE sensors applied to the frescoed wall, is to detect the possible Acoustic Emission signals from a vertical crack and from a region of the wall in which the frescos show a detachment of plaster. The operations necessary for the AE sensors bonding to the wall are carried out by a group of restorers, which have prepared a film of Japanese paper, on the surface of which is coated a thin layer of "Paraloid". The "Paraloid" is an acrylic resin (methyl acrylate soluble in ketones, esters, hydrocarbons and chlorinated hydrocarbons) and is used in the field of restoration as a consolidant at low concentrations (2,4%) or as an adhesive at higher concentrations. It allows an excellent waterproof performance and has the advantage of being reversible and long-term stable. The layer of "Paraloid" forms a good protective base for the AE sensors bonding with silicone glue. The sensors are applied to monitor both the vertical crack and the detachment of the plaster (Fig.5).
RkJQdWJsaXNoZXIy MjM0NDE=