Externally bonded reinforcement in grooves (EBRIG) technique to postpone debonding of FRP sheets in strengthened concrete beams

Recently a new method for flexural strengthening of concrete beams with FRP sheets, named as grooving method (GM) with the special technique of externally bonded reinforcement on grooves (EBROG), has been introduced as alternative to conventional externally bonded reinforcement (EBR). Based on some experimental investigations, the EBROG method can considerably postpone the debonding phenomenon and in some cases may completely eliminate it. The aim of the current study is to introduce and to examine another improved strengthening procedure by using the GM method when the FRP sheets are in direct contact with the internal surfaces of the grooves on the tension face of concrete beam in a wet-lay-up application. This technique is named externally bonded reinforcement in grooves (EBRIG). For this purpose, 32 beam specimens with dimensions of 120 × 140 × 1000 mm were cast, strengthened with one, two or three layers of FRP sheets and then subjected to four-point flexural loading. Results showed considerable increase in ultimate limits for beams strengthened with EBROG and EBRIG techniques compared to those strengthened with EBR method. The EBRIG technique performed as good as EBROG for one layer of strengthening FRP sheet; however, it permitted for higher failure loads and displacements compared to EBROG method when multiple-layer FRP sheets were used.