Bond performance of FRP bars in plain and fiber-reinforced geopolymer under pull-out loading

Abstract

Geopolymer-bonded fiber-reinforced polymer (FRP) bar is an emerging strengthening system for concrete structures, owing to the excellent geopolymer/concrete bond and the superior moisture and fire resistance of geopolymer matrix (compared to organic bonding adhesives). To apply this strengthening system, the bond performance between FRP bars and geopolymer should be properly understood. In this study, pull-out tests on 81 specimens with a carbon FRP (CFRP) bar embedded in plain and fiber-reinforced geopolymer were conducted. Key factors including the strength of geopolymer (different mass ratios of fly ash and slag), bar embedded length (5, 10, and 15 times the bar diameter), fiber volume fraction in geopolymer (0, 1%, and 2%), and bar diameters (3 mm, 6 mm, and 10 mm) were explored. The results showed that (1) an increase in geopolymer strength improves the bond strength; (2) increasing embedded length (from 5db to 15db) would reduce the average bond strength (by 20–30%); and (3) adding steel and PVA fibers in geopolymer had a marginal effect on the bond strength. Furthermore, a modified bond strength model of CFRP bars in the geopolymer mortar is proposed based on the current experimental results. The findings lay the groundwork for understanding the bond behaviour of FRP bars in geopolymer, which is critical for the successful application of geopolymer-bonded FRP bar strengthening system.