Influence of Bond Conditions on the Confinement Effectiveness of FRCM Composites

The behavior of Fabric Reinforced Cementitious Composites (FRCM) have shown to be highly dependent on the bonding conditions of both fabric-matrix and matrix-substrate interfaces. One of the main applications involving FRCM composites concerns the confinement of axially loaded concrete elements. The present paper presents the results of an extensive experimental campaign carried out with the aim of evaluating the confinement effectiveness of FRCM composites when applied with different bond conditions. Cylindrical specimens were confined with two layers of carbon FRCM and tested under cyclic axial loading. The following bond aspects were analyzed: overlapping length, fabric weight, discontinuous and continuous FRCM layer application and fabric impregnation (no impregnation (dry), epoxy resin and fluid cementitious matrix impregnation). Experimental results are discussed in terms of failure modes, axial stress-strain curves, plastic strains, strength and stiffness deterioration due to cyclic loading. The results highlight that bond conditions can influence the confinement effectiveness of FRCM jackets. Among the investigated bond variables fiber impregnation proved to have the highest affect both in terms of axial strength enhancement and axial strain capacity. Lastly, the main parameters that define unloading and reloading paths during axial cyclic loading were analyzed and new formulations were proposed for their prediction in FRCM-confined concrete.