A Review: Effect of Corrosive Environment on Bond Strength of FRP Bars in Different Grade of Concrete

Abstract

Corrosive marine environments degrade FRP bar-concrete bond through resin softening, interface microcracking, and loss of mechanical interlock, with degradation varying significantly across M20-M60 concrete grades where lower strengths suffer higher relative losses of 15-25%. This review synthesizes 24 experimental studies (2018-2025) on GFRP, BFRP bars with sand-coating, ribbing, fibre-wrapping in normal, seawater sea-sand, and geopolymer concretes tested via pull-out, hinged beam, double-shear methods per IS 456:2000 and ACI 440 provisions. Seawater wet-dry cycles cause maximum 5-10% bond loss after 250 days versus 3-5% immersion; higher grades (C45-C60) boost initial stiffness 50-100% but amplify relative degradation in M20-M30 mixes. Sand-coated surfaces outperform ribbed by 3-8% post-exposure through protected resin interfaces; anchorage shifts failure to tensile rupture achieving 85-95% f_fu utilization. Meta-learning confirms temperature-sulphate cycles-concrete grade as primary drivers. Findings identify optimal grade-surface combinations for coastal structures while highlighting gaps in Indian Zone III-IV validations and 5-year field data.

Introduction

Coastal infrastructure in India faces severe durability challenges from chloride-rich seawater, wet-dry cycles, and salt crystallization, which rapidly degrade steel reinforcement. Fiber-reinforced polymer (FRP) bars (GFRP, BFRP, CFRP) offer corrosion resistance, high tensile strength (800–1300 MPa), and low density, but have 40–60% lower bond strength than steel due to smooth surfaces, lower modulus, and reliance on mechanical interlocking. Surface modifications—sand-coating, ribbing, fiber-wrapping—enhance bond, yet seawater, wet-dry, and sulfate exposures still cause resin swelling, microcracking, and fiber-matrix debonding.

Literature shows sand-coated and anchored FRP consistently outperform ribbed configurations, retaining 85–95% of tensile capacity after seawater/wet-dry exposure. Higher-grade concretes (M40–M50) mitigate relative bond losses (5–10%), while lower grades (M20–M30) suffer 15–25% degradation. Geopolymer concretes with glass/basalt fibers improve bond 15–20% over OPC. Experimental methods include pull-out, beam-end, and hinged beam tests under immersion, wet-dry, chloride ponding, and hygrothermal-salt cycles.

Code provisions (IS 456:2000, IS 10262:2019, ACI 440.1R-15) guide cover, development length, and bond stress design. FRP-specific guidance suggests development lengths 1.5–2× steel, with sand-coated/anchored M40–M50 achieving <10% bond loss, maintaining serviceability under XS2–XS3 marine exposures. Wet-dry cycling is the most aggressive, while anchorage shifts failure from pull-out to bar rupture (≥85% f_fu). These findings support optimized FRP-RC design in coastal India, offering corrosion immunity, durability, and lifecycle cost savings over steel.

Conclusion

The review of experimental studies and proposed testing methodology demonstrates that corrosive environments significantly alter FRP bar-concrete bond performance across M20-M60 grades even with surface treatments and anchorage. Wet-dry seawater cycles cause maximum 5-15% ?_max reduction versus 3-5% immersion, confirming repeated moisture ingress hydrolyzes resin interfaces more severely than constant exposure, while sand-coated configurations retain 92-95% capacity outperforming ribbed (82-88%) through protected mechanical interlock. Lower grades M20-M30 suffer highest relative losses (15-25%) due to microcracking propagation and reduced confinement despite lower absolute bond stresses; M40-50 optimal achieving <10% degradation with anchorage shifting failure to rupture ?85% f_fu per ACI 440 targets. Geopolymer concretes yield 15-20% bond gains over OPC equivalents through matrix enhancement, though Indian coastal field data remains sparse for XS2-XS3 validation. Meta-learning ranks temperature-cycles-grade hierarchy guiding coupled exposure protocols beyond single-factor testing. For marine FRP-RC design, IS 456 lacks specific provisions forcing ACI 440-conservative l_d (1.5-2x steel) that underutilizes ma-terial advantages; sand-coated M40 + anchorage recommended minimizing +20-30% development increases while ensuring ser-viceability. Overall study highlights surface-grade-anchorage optimization essential bridging laboratory trends with practical coastal infrastructure demands under Indian standards, positioning FRP superior to steel for 75-year durability in Zone III-IV ports saving lifecycle repair costs.

References

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Copyright

Copyright © 2025 Hardik Bele, Deepa Telang. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.