Experimental evaluation of bond behavior of post-installed GFRP and steel reinforcements using different adhesives

The existing design codes lack specifications for the use of glass fiber-reinforced polymer (GFRP) bars in post-installation applications, and research on this topic is scarce. This study investigates the bond performance of the post-installed GFRP and steel reinforcement bars through pull-out tests using three commercial chemical adhesives. Seventy cylindrical specimens (60 post-installed, 10 cast-in-place) with diameters of 15 cm and heights of 30 cm were prepared. Post-installed samples featured anchor bars with 5d, 10d, and 15d embedded lengths (where d is the rebar diameter), tested under dry and wet conditions. Compressive strengths of 25 MPa and 35 MPa were used. Three different commercial adhesive types were utilized in this research: pure epoxy adhesive (adhesive A) and two epoxy acrylate adhesives (adhesives B and C). Adhesive A demonstrated improved bond strength by up to 75% with longer embedded lengths and higher concrete compressive strengths when compared to adhesives B and C, regardless of moisture conditions. All specimens showed concrete rupture or splitting failure, proving the effectiveness of the epoxy resins as bonding agents. The findings emphasize the significance of adhesive selection and design parameters in improving bond performance.