Carbon Fabric Reinforced Cementitious Mortar confinement of concrete cylinders: the matrix effect for multi-ply wrapping

The confinement of columns is one of the most used strengthening techniques for reinforced concrete (RC) framed structures being able to improve both the axial strength and ductility. In the last decades, technological advances provided different tools/solutions for the achievement of an effective confinement, among all: the RC-jacket, the steel ties, the fibre reinforced polymer (FRP) wrapping, and lastly the fabric reinforced cementitious mortar (FRCM) plastering. The proposed research aims to investigate two open-issues and their combination related to the use of the FRCM, such as the multi-ply confinement and the role of the inorganic matrix with respect to the confinement effectiveness. At this scope, a set of pure compression tests were carried out to evaluate the representative laws of the mechanical behaviour of confined columns, namely the axial stress versus axial/lateral strain. Consequently, the axial strength and ductility gains were computed. In particular, the investigated variables were the grade of the inorganic matrix, by varying its compressive strength (i.e. ∼25 MPa and ∼50 MPa), and the number of plies (i.e. 1, 2 and 3). The results showed that the higher gain in term of axial strength and ductility is met by increasing the mortar's compressive/tensile strength and, at the same time, the number of plies. Lastly, available design-oriented analytical models were found able to predict the FRCM-confinement effect in terms of strength. In addition, an available analysis-oriented model accurately foreseen the axial stress–strain law when dealing with the high-grade strength matrix confining in both single, double and triple layer of FRCM-system.