State of the Art of Steel Reinforced Grout Applications to Strengthen Masonry Structures

Load-bearing unreinforced masonry structures represent a significant proportion of the building stock in several countries worldwide, and include historical constructions that belong to cultural heritage. Because of the limited tensile strength of unreinforced masonry, fiber-reinforced composites are an effective strengthening technique, which has already been widely used, especially in seismic prone areas, to delay the onset of collapse mechanisms of the entire structure or portions of it. Steel reinforced grout (SRG), which consists of steel textiles embedded in a cement or lime based mortar, is a particularly appealing alternative to fiber-reinforced polymer (FRP) composites, as well as to other mortar based composites (i.e., fabric reinforced cementitious matrix, FRCM), especially when applied to masonry structures. This paper sheds light into the retrofitting of masonry structures with SRG, providing an overview of the experimental investigations carried out in the laboratory and in the field on full-scale structural members. SRG proved effective for improving the out-of-plane flexural strength and deflection capacity of masonry walls (for which three or four-point bending tests and shake table tests were performed), the load-bearing and deflection capacity of vaults (tested both in the laboratory and in the field under quasi-static vertical loads), and the compressive strength of columns (subjected in the laboratory to centred axial load). Further research needs are identified, which are considered useful for the development of design guidelines.