A Study of the Bond of GFRP Rods in Concrete and the Internal Forces of Concrete Beams Reinforced with Rebars and a GFRP Rod

Abstract

The objective of this research was to study the bond strength of GFRP (Glass Fiber Reinforce Polymer) rods embedded in concrete and to study the internal force behavior of concrete beams strengthened with rebars and a GFRP rod by using Near-Surface-Mount system (NSM). Concrete sample for bond strength test was a cubic size of 150 mm, whereby a GFRP rod was embedded in the concrete at different embedment lengths and edge distances from the concrete surface. The rebar or GFRP bar was bonded with epoxy inside the prepared grooves. The beams used to study the internal force behavior had a cross section of 150x250 mm and a length of 2000 mm. Reinforced concrete beam samples were strengthened with a rebar and a GFRP rod, and they were tested under four-points bending. Test results had showed that bonding of a GFRP rod to concrete groove with epoxy could provide better bond strength than embedding GFRP rods directly into concrete. An increase in embedded length of the GFRP rod into the concrete resulted in a greater pullout load, but the bond strength would decrease. In addition, increasing the concrete cover (edge distance) of the GFRP rod did not increase the bond strength. The investigation of the internal forces in concrete beams revealed that concrete beams reinforced with GFRP rods showed lesser bending force and stiffness after crack than those reinforced with rebars, because GFRP rod has a lower modulus of elasticity than rebar. Moreover, strengthening concrete beams with GFRP rod would provide greater bending force compared to the control beam, but they did not increase the stiffness of the beams after crack.