Carbon Fiber Reinforced Polymer (CFRP) Composite Spirals as Confinement Reinforcement for Concrete under Axial Compression

Abstract

The use of fiber composites in structural strengthening applications has been implemented for many years. Among others, this type of material has been employed as means to confine concrete and achieve superior material behavior. Confinement can be achieved either by wrapping the concrete with FRP fabrics or by embedding FRP stirrups or spiral (helical) reinforcement in concrete. Although FRP spirals have been used as reinforcement in concrete members, this was primarily in the form of FRP bars used as shear reinforcement in RC members under flexure. Some studies have been conducted using FRP spiral strips that were bonded on the outside face of cylindrical specimens and their confinement effect on concrete under axial compression was evaluated. This study deals with the experimental testing of concrete cylindrical specimens that utilize embedded carbon FRP (CFRP) composite spiral reinforcement, a unique application with limited investigation as to its effect on concrete confinement. Standard (300 mm x 150 mm) concrete cylinders were cast both with and without the embedded CFRP spiral. The cylinders were tested in axial compression to determine the effect of the CFRP spiral on their strength and ultimate deformation. This study contributes to the field of concrete confinement and in an area that is not well investigated especially when the FRP spiral is embedded into concrete. Experimental results indicate very significant improvements in ultimate strength and strain with more the enhancement reaching 116% for the strength and 147% for the strain. Comparing energy absorption capacity of the CFRP spirally confined concrete with the unconfined concrete, the improvement is even higher and reaches 320%. Therefore, the use of embedded CFRP spiral to confine concrete is effective and provides significant confinement and enhances concrete properties.