Developing Bond-Slip Relationships for Adhesively Anchored GFRP Bars Using Hinge Beam Tests

Glass fiber-reinforced polymer (GFRP) bars are becoming more common in applications where corrosion resistance is desired, such as bridge decks and barriers. If retrofitting reinforced concrete with GFRP, or if adding a GFRP reinforced component to existing concrete, GFRP bars are often connected using adhesive anchors. In this process, a hole is drilled into concrete, adhesive (grout or epoxy common) placed in the hole, then GFRP bars inserted. Bond quality is often assessed using pullout tests on adhesively anchored bars. Though this test method is relatively easy to set up, results may not represent of stress states experienced in flexural members. Hinged beam tests are an accepted approach for developing bond-slip relationships used for design codes and standards for concrete reinforced with either steel or GFRP. A novel technique of fabricating hinge beam tests with adhesively anchored GFRP bars is presented in this study. This process involves casting a beam with a placeholder bar, removing that bar, drilling a hole for adhesive anchoring, then using a process analogous to grouting a post-tensioning duct to ensure that embedded bar length is sufficient. Trial processes showed that epoxy could flow around the bar without voids forming or leaking outside of the anchorage test region. Hinged beam tests on high modulus (60 GPa nominal stiffness) bars with 17.1 mm diameter GFRP bars bonded over an anchorage length of 225 mm with an epoxy adhesive were completed and compared to tests on the same bar without adhesive. Bars without the adhesive reached an average maximum bond strength of 12.1 MPa and failed at the interface between the GFRP bar coating and the core of the bar. Bars with epoxy adhesive reached an average bond strength of 11.2 MPa and failed at the interface between concrete and epoxy. Both types of bars were then successfully fit using the modified BPE model proposed by Consenza (1995) for GFRP bars in concrete. Results, including post-test inspections, show that the proposed technique was effective for assessing the bond-slip response of GFRP bars adhesively anchored to concrete.