NSM and hybrid techniques for retrofitting corroded RC beams using GFRP bars

Abstract

This is an experimental study on the flexural performance of corroded reinforced concrete (RC) beams strengthened by three different methods using Glass Fibre Reinforced Polymer (GFRP) bars. Three methods of strengthening were used: the traditional method of replacing damaged concrete covers and installing GFRP bars, the near-surface mounted (NSM) method, and a hybrid method involving mechanical fasteners and the NSM method. In total, seventeen RC beams were constructed one of which was used as a control specimen, while the remaining sixteen were divided into four groups and were exposed to accelerated corrosion to reach a theoretical mass loss of 3.5 to 30% in tensile steels. Three groups of corroded beams were strengthened using the three methods mentioned, while the other group received no strengthening. Then, all the beams were tested under four-point loading to determine their load-deflection response, stiffness, ductility, failure mode, and strain of the GFRP bars. The results showed that the conventional strengthening method using GFRP bars was relatively efficient in restoring the load-bearing capability of corrosion-damaged beams. However, sufficient anchorage length for the GFRP bars was required to achieve high ductility. The NSM method effectively improved the load-bearing capacity of beams with low corrosion levels; however, increasing the corrosion level caused the strengthened beams to fail prematurely due to concrete cover separation. It was observed that the hybrid strengthening method improved the load-bearing capacity of corroded beams while maintaining their ductility by preventing premature failure due to concrete cover separation.