Bond strength of post-installed GFRP bars in beam-column connections

Post-installed reinforcement in concrete is used to connect a new concrete member to an existing concrete structure. Design using post-installed reinforcing bars is gaining acceptance due to design flexibility, formwork simplification and the ability to have horizontal, vertical, and overhead applications. Research has been conducted on the efficacy of post-installed steel reinforcement in concrete structures. However, steel corrodes in aggressive environments resulting in a loss of bond strength and serviceability. Alternatively, glass fiber-reinforced polymer (GFRP) bars can be used as post-installed reinforcement. GFRP bars are gaining acceptance in the structural field due to their corrosion resistance and high strength to weight ratio. This research presents an experimental study with GFRP bars from three manufacturers, which were post-installed using an epoxy-based adhesive. Eight specimens were constructed and tested monotonically to failure. A specimen was composed of two identical vertical elements, which were anchored into the base of the structure using post-installed GFRP bars. The specimens were designed to simulate a rigid connection of two cantilever beams to a column. The concrete compressive strength for all the specimens was 3 ksi (20.68 MPa) and the size of all the post-installed and cast-in-place bars was #4 (#13). The specimens were tested with bars installed at 6 and 11.5 in. embedment depths (15.24 and 29.21 cm). The results from the specimens with bars installed at a longer embedment depth indicated an increase in the loading capacity and the ductility compared to the specimens with bars installed at a shorter embedment depth. The evaluation of bond strength was done by comparing the type of failure and load capacity of the post-installed GFRP bars with the cast-in-place steel and GFRP bars. The specimens with cast-in GFRP bars exhibited a bond-slip failure, whereas the specimens with post-installed GFRP bars had a splitting failure (concrete cone breakout), indicating a stronger bond of the post-installed GFRP bars with concrete.