Detachment monitoring of repair mortar applied to historical masonry stone by acoustic emission technique

In the restoration of historical masonry walls, the plaster detachment frequently occurs because of the long-term mechanical incompatibility of repair mortar. An innovative laboratory procedure is described for evaluate the mechanical adhesion of the new repair mortar applied in the restoration work at the Sacro Monte di Varallo Special Natural Reserve (UNESCO heritage site). The acoustic emission (AE) monitoring technique has allowed to assess the damage localization and to evaluate the repair mortar applied to historical masonry stone. This non-destructive methodology was able to identify defects and damages in masonry structures. Through shear tests, the specific geometry of assembled specimen can verify the detachment process of repair mortar. The AE technique permits to estimate the amount of energy released from fracture propagation in adherence surface between mortar and stone. The authors have elaborated a numerical simulation to follow the experimental data. The evolution of detachment process of mortar in a coupled stone brick – mortar system was analysed by means of the Acoustic Emission technique, which can improve the numerical model and predict the type of failure in adhesion surface of repair plaster. Therefore, the experimental procedure was able to characterize the mechanical behavior of detachment mortar, useful for selection of repair plaster applied to historical masonry stone.