Experimental investigation on bond behaviour of the GFRP bars with normal and high strength geopolymer concrete

The study presents the experimental investigation of bond performance of normal and high-strength geopolymer concrete and Glass Fibre Reinforced Polymer (GFRP) bars. The effects of bar diameters, embedment lengths, and concrete grades on maximum pullout load and failure characteristics are investigated. When the adhesive and residual strengths of GFRP bond specimens were compared to steel specimens, the former demonstrated remarkable performance despite having differing surface properties. An energy-based equivalent bond strength approach is proposed to examine pre-peak bond performance, which demonstrating that the decreasing rate of strength is faster for higher diameter and embedment, showing a drop in bond performance. Pullout failure was noted in smaller diameter bond specimens, where the shear strength between the ribs and the GFRP bar controlled the bond strength. Concrete split failure occurs for 12 mm specimens with embedment lengths greater than 5d in both GPC40 and GPC60. Specimens with 16 mm, excluding G-16-5d-60, demonstrated concrete split failure for all embedment lengths and concrete grades; bond strength is determined by the concrete shear strength. Enhancing the concrete's compressive strength has a beneficial impact on the bond strength as it increases ranging, from 14.57 to 32.12%. Analytical models such as mBPE and CMR were employed to derive the mathematical expression for the bond stress versus slip curve. It was found that the curves of CMR model were typically closer to experimental curves than the mBPE model.