Assessment of reinforced overlay for masonry retrofitting: Lime vs cementitious plaster

Reinforced overlay is a very common retrofitting technique adopted in existing masonry buildings to improve their performance under seismic action, both in-plane and out-of-plane. The most traditional and widespread approach considers the use of cementitious mortar as plaster with steel meshes as reinforcement. However, cementitious materials may raise compatibility problems with the base material and sustainability issues, thus the use of lime mortar should be preferred. This paper presents the results of an experimental program aimed at assessing the contribution of the reinforced plaster strengthening system in increasing the load carrying capacity of masonry walls, comparing the performance of cementitious and lime mortar plaster. Cyclic diagonal compression tests were performed under displacement control. Unreinforced specimens were also tested as reference for the improvement evaluation. The results showed an improved performance with respect to the unreinforced ones for both the materials (cementitious and lime mortar), in terms of both strength and deformation capacity. The peak load seemed to be not significantly affected by the type of plaster, while higher displacement at the ultimate load was observed in case of lime mortar. Finally, an analytical method formulated to predict the strength of walls retrofitted with cementitious reinforced plaster was applied to check its validity also in case of lime-based plaster.