Strengthening and Repairing Unreinforced Masonry Walls by Nano-Composite Steel Fiber Reinforced Mortar Overlays

It is well known that the poor tensile strength properties of unreinforced masonry makes such a material particularly vulnerable to lateral loads that apply shear actions on the masonry member. The lack of an adequate shear resistance may become critical especially when masonry constructions are located in areas where earthquake actions can put a strain on their actual seismic resistance. In view of this, several researches have been carried out in the last decades to develop strengthening and repairing techniques, which allow the structure to meet the needed resistance demand. In this context, advanced materials like nano-composites having high performance mechanical and protection properties can be exploited for structural retrofitting and rehabilitation. The paper focuses on the results obtained from a series of quasi static reverse cyclic tests carried out on unreinforced clay-brick masonry shear walls strengthened or repaired by using thin layers of Steel Fiber Reinforced Mortar (SFRM) applied on both sides of the member. The composite material employed in this research is made of nano-particles of calcium aluminates and corundum and it is reinforced by short steel fibers, having high strength; the significant mechanical and water-proof properties make the adopted SFRM a promising technology to protect and improve the seismic resistance of masonry structures. A comprehensive discussion of the obtained experimental results will point out the main advantages and drawbacks of the proposed strengthening technique.