Torsional strengthening of RC beams using NSM CFRP rope and innovative adhesives

The strength of reinforced concrete (RC) members can be increased by bonding carbon fibre-reinforced polymers (CFRP) using externally-bonded reinforcement (EBR) and near-surface mounted (NSM) techniques. However, to date few studies in the area of torsional strengthening have been performed using NSM methods. Although the efficacy of increasing the flexural and shear strength of RC beams has been well reported using the NSM technique bonded with epoxy resins, the poor performance of epoxy in high-temperature environments and toxic fumes have been motivating factors for using new cement-based adhesives as a replacement adhesive for epoxy in several studies. This paper investigates the torsional behaviour of RC beams strengthened using NSM FRP laminates and FRP ropes. An epoxy adhesive was used in four beams and a new cement-based adhesive was utilised in the remaining four beams and used to evaluate the torsional capacity. Both CFRP laminates and CFRP ropes were embedded into pre-cut grooves. According to the results, the torsional behaviour of the beams strengthened with CFRP ropes was superior to that of the beams strengthened with CFRP laminate when using epoxy resin and cement-based adhesive. Generally, the epoxy was more effective in increasing the torsional strength than the cement-based adhesive.