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

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.