Experimental tests on FRCM strengthening systems for tuff masonry elements

Abstract

Composite materials consisting of high-strength fibers embedded in inorganic matrix (Fiber Reinforced Cementitious Mortar materials, FRCM) are becoming more and more widespread as strengthening technique for existing masonry structures because of the higher compatibility of the inorganic matrix with the masonry supports compared with the epoxy adhesives, the lower sensitivity to debonding phenomena at the interface, and the ‘grid’ configuration of the reinforcement, particularly suitable for strengthening bi-dimensional elements. Conversely, the use of lime or cement-based mortar implies that attention has to be payed also to the bond behavior between the fibers and the matrix, since sliding phenomena and cohesive failures in the mortar frequently occur. Thus, for the FRCM materials the knowledge of the bond behavior both at the fiber/matrix and at the composite/substrate interface is fundamental to correctly assess their performance as strengthening of masonry elements.The experimental tests discussed in this paper show different aspects of the bond behavior of the FRCM materials in order to validate an experimental methodology for such a strengthening technique. In particular, tensile tests on coupons made of different FRCM materials were carried out in order to investigate the interaction between fibers and mortar and the bond strength at the fiber/mortar interface. Then, the bond behavior between different FRCM systems and a masonry substrate made of Neapolitan yellow tuff was investigated by shear bond tests according to a single push-pull set-up. The experimental tests were carried out on three types of fibers embedded in cement-based grouts: a balanced glass grid (G-FRCM, i.e. Glass Fibers Reinforced Cementitious Mortar system), and two types of unidirectional fabric made of steel cords (SRG, i.e. Steel Reinforced Grout system) with different density. The readings obtained with traditional measuring instruments were integrated with those obtained by the Digital Image Correlation (DIC) technique.