Experimental investigation into the use of NSM FRP to increase the torsional resistance of RC beams using epoxy resins and cement-based adhesives

Abstract

Carbon fibre-reinforced polymers (CFRPs) have been used to increase the strength of reinforced concrete (RC) members using both externally bonded reinforcement (EBR) and near surface mounted (NSM) techniques with a great deal of success. However, currently no studies have been conducted on torsional strengthening using NSM methods as current research on torsional strengthening has been conducted using EBR techniques only. It is well documented that flexure and shear strength of RC beams has been improved using NSM strengthening technology applied with epoxy adhesives. However, due to epoxy adhesive problems associated with toxic fumes and poor performance in high-temperature environments, a new cement-based adhesive has been developed and used as an alternative to epoxy in several studies. This paper reports on experimental results of ten RC beams tested in torsion using a specialized torsional rig system. Two control beams were considered and eight beams strengthened with CFRP laminates applied to all four faces of the beam and embedded into pre-cut grooves using the NSM technique were prepared. An epoxy adhesive was used in four beams and a new cement-based adhesive was used as a substitute for epoxy in the remaining four beams. For each type of adhesive, two different spacings between the grooves were examined. The performances and the ultimate strengths of the beams are presented and the results expressed in terms of the maximum torsional capacity with respect to the peak angle of twist. According to the results, the torsional behaviour of the beams was improved in the strengthened beams to varying degrees when using epoxy resin as the bonding agent. On the other hand, the NSM technique with the cement-based adhesive was also an effective method in increasing the torsional strength.