Experimental study on concrete columns strengthened with non-adhesive carbon fibre spirals under axial compression

Fibre-reinforced polymer (FRP) has little effect on confining concrete in fire because of the resinae adhesive invalid, a new strengthening method for strengthened concrete members with non-adhesive carbon fibre spirals was proposed by the third author in order to alleviate this problem. This paper presents an experimental study on the axial compression behavior of this carbon fibre spirals strengthened concrete column (CSSC) at room temperature. The particle image velocimetry (PIV) technique was used to measure the deformation. The test program considered the effects of the number of fibre layers, the width of fibre strap, the position of grout and fibre connection. The test results show that compared with the corresponding plain concrete column, the bearing capacity of CSSC is 20% higher, and the ductility increases by 1~2 times. The failure process of CSSC columns reveals no bursting. The mechanical properties of CSSC are improved with an increasing number of fibre layers. A wider fibre strip width may cause a large angle between the fiber direction and the horizontal, which decreases the bearing capacity of CSSC. It would increase the bearing capacity of CSSC if grout attached to the interface between concrete and fibres. Attaching grout to the outside of fibres improves the transverse ultimate strain of CSSC.