Axial strength and deformability of concrete confined with natural fibre-reinforced polymers

This paper presents the results of an experimental study on the compressive behaviour of concrete confined by natural fibre-reinforced polymer (NFRP) jackets which are formed by embedding sisal fibres in an epoxy resin matrix. The sisal fibres are one of the cost-effective materials for use in seismic strengthening applications where a moderate increase in strength and ductility is required. This study has two main objectives: the first is to investigate the effectiveness of NFRP composites in increasing the strength and deformability of confined concrete. For the second objective, the performance of existing strength models developed for conventional synthetic fibre-reinforced polymers is assessed. For this, 36 concrete specimens were tested under uni-axial compression. The study parameters covered the NFRP thickness, concrete strength and cross-sectional shape. Test results indicated that the NFRP confinement is significantly effective in increasing the strength and deformability of confined concrete. Furthermore, it is found that none of the existing considered models is capable of accurately predicting the ultimate strength and strain of NFRP-confined concrete. Finally, new strength models are proposed to predict the compressive strength of circular and square sections. The strengths predicted by the proposed models are found to have a good agreement with experimental results.