EFFECT OF CONCRETE STRENGTH AND GROOVE DIMENSION ON PERFORMANCE OF GROOVING METHOD TO POSTPONE DEBONDING OF FRP SHEETS IN STRENGTHENED CONCRETE BEAMS

A major obstacle in using FRP sheets for flexural and shear strengthening has been debonding failure, which leads to premature and noneconomic failure of the strengthened element. Surface preparation of concrete member has been widely used to provide good bonding of the composite sheet onto concrete surface; however, it is found to be only partially effective in delaying debonding. Recently, Grooving Method (GM) has been introduced as a novel substitute for conventional surface preparation in Externally Bonded Reinforcement (EBR) strengthening of concrete beams. Although the previous experiments have shown that grooving method can postpone or even eliminate the debonding of FRP sheets from concrete substrate, the method is still in its early stages of development and awaits further research for maturation. The present study is an attempt to examine the effectiveness of grooving method for beams with different concrete compressive strength; also, to investigate the effects of groove depth and width on controlling FRP debonding for concrete specimens with different compression strengths. The experimental specimens included 44 concrete beams, which with three samples per beam resulted in a total of 132 specimens. Initially, two grooves of varying widths and depths were made in each specimen. The grooves were then filled with an appropriate epoxy resin and the FRP sheets were bonded onto the concrete surface. After the resin had hardened, the specimens were subjected to the four-point flexural test. The experimental results showed the superiority of grooving method on conventional surface preparation for all four experimental categories with different compressive strength of concrete. The results also showed that a depth of 10 mm may be the optimum groove depth for all four experimental categories.