Experimental investigation of bond and cracking behaviours in gfrp-reinforced concrete members

Although Glass Fiber -Reinforced Polymer (GFRP) reinforcing bars are becoming commonplace, their mechanical properties - low modulus of elasticity and high tensile strength - result in design of GFRP-reinforced concrete members (GFRP-RC) often being governed by deflection and crack control at the serviceability limit state. Bond performance of GFRP bars impacts the crack control provided and, due to the empirical nature of bond characterization in design, bond of GFRP remains described in relation to that of steel. To describe the bond performance of GFRP bars, a bond -dependent coefficient, kb, is adopted in design guides and standards. The bond and cracking behaviours of GFRP bars embedded in concrete - including the estimation of kb - were investigated through 80 pull-out and 12 prism tension tests. The evaluation of kb using ASTM D7913 pull-out, confirming the bond performance using a smaller number of prism tension tests, is proposed. The results showed that values of kb determined from pull-out test were about 15-20 % greater than those estimated by prism test. Nonetheless, kb values determined from both tests are similar and follow the same trends. These data obtained in this experimental programme supplemented an extant database of 137 comparable pull-out test results covering a range of GFRP bar and concrete parameters. The study concludes that ASTM D7913 pull-out tests are suitable for assessing minimum GFRP reinforcing bar bond criteria although more complex prism tests are likely required to accurately assess kb.