Confinement of concrete with FRCM: Influence of bond aspects under cyclic axial loading

Bond aspects may significantly influence the effectiveness of Fiber Reinforced Cementitious Matrix (FRCM) jackets as confining system. Among them, this paper focuses on the following variables: the overlapping length, the equivalent thickness of the fibers (directly related with the fabric weight), fibers coating presence (preimpregnated with epoxy resin or fluid cement paste), and lastly, the reinforcement configuration (continuous or discontinuous layers). For this scope, an experimental campaign was carried out on cylindric specimens, subject to cyclic axial loading, strengthened with two layers of carbon-based FRCM (CFRCM). Failure modes, axial stress–strain curve, strength and stiffness deterioration and, lastly, plastic strains were analyzed. Experimental results indicate a clear effect of the investigated parameters on the overall effectiveness of the confining jackets: the best results were obtained when carbon fibers are epoxy-coated, recalling that for making the application feasible, a relatively large mesh size and a low degree of coating impregnation should be used for the textiles. Lastly, new relationships to predict the main parameters that define the cyclic behavior of confined concrete are proposed and compared with those found in literature for other confining systems (based on fiber-reinforced polymer FRP and transverse steel).