Study of the matrix-fiber bond behavior of carbon and glass FRCM composites

Strengthening and retrofitting of existing reinforced concrete (RC) elements have been gaining interest in recent decades. Among the strengthening solutions available, fiber reinforced composites present certain advantages, such as high strength-to-weight ratio and low invasivity, which make them attractive in some applications. In particular, fiber reinforced polymer (FRP) composites have been successfully employed for bending and shear strengthening and for confinement of axially loaded elements, however they suffer from UV degradation, (relatively) high temperature exposure, and cannot be applied onto wet surfaces. To overcome these limitations, which are mostly related to the use of organic binders (usually epoxy resins), a new type of composite comprised of a fiber mesh embedded within an inorganic matrix has recently been developed and is referred to as fiber reinforced cementitious matrix (FRCM) composites. While FRCM composites have proven effective for strengthening RC elements, each specific composite presents a different behavior and needs to be properly characterized. In this paper, the results of single-lap direct-shear tests of carbon and glass FRCM-concrete joints are presented and discussed. Specimens with different composite bonded lengths were tested in an attempt to identify the effective bond length of each composite. The debonding stress experimentally obtained for carbon FRCM composites is also compared with that obtained through a fracture mechanics approach based on fiber strains measured on the same material using strain gauges bonded to the longitudinal fibers.