Acoustic emission and numerical analysis of the delamination process in repair plasters applied to historical walls

The delamination process of plasters applied for the repair work of historical walls was often caused by humidity phenomena or physical-mechanical cycles stress. In this paper a new experimental methodology has been conducted by testing in the laboratory mixed stone-mortar specimens and analyzing the delamination progression. The experiment simulated the recurring delamination in the stone walls of the Sacro Monte di Varallo, an UNESCO site in Piedmont (Italy). Through the monitoring by means of acoustic emission (AE) sensors during the tests it was possible to qualify the different fracture modes characterizing the delamination process, which takes place during the tests at the interface between plaster mortar and stone block. AE is a non-destructive technique useful to estimate the amount of energy released from fracture propagation in the adherence surface between mortar and stone. The experimental results confirmed the stick-slip behaviour that characterises the friction process inside the delamination surface between repair mortar and masonry stone.