Improved GFRP Rebar for Reinforced Concrete Structural Application

Abstract

AbstractImprovements in state-of-the-art GFRP rebar materials have demonstrated higher durability in accelerated environmental corrosion resistance testing, higher creep rupture and fatigue endurance limits. Case studies of bridge rehabilitation projects have demonstrated the value of glass fiber-reinforced polymer (GFRP) in building longer-lasting, maintenance-free reinforced concrete (RC) infrastructure. The recent ACI Strategic Development Council (SDC) durability study sampled core extractions from eleven 15 to 20-year GFRP-RC bridge structures. The analysis confirmed the GFRP exceeded the implications of accelerated durability tests from AASHTO and ACI standards with less than a 0.15% reduction in strength per year. Based on this study, if the estimated strength reduction due to aging was less than 15% over a period of 100 years assuming linear degradation, then the 0.7 strength reduction factor (CE) adopted by most design guides to account for environment degradation appears overly conservative (Nanni et al., Durability study of GFRP bars extracted from bridges with 15 to 20 years of service life, Report for strategic development council of the American Concrete Institute, Farmington Hills, MI, June 2019, p 732019). The environment strength reduction factor is under evaluation for refinement. Recent improvements in state-of-the-art GFRP rebars have demonstrated higher sustained load creep rupture and fatigue endurance limits. This paper examines the ACI 440.3R-B.8 creep rupture strength data from state-of-the-art GFRP rebar supporting higher endurance limits for the industry. In RC bridge design, the cyclic fatigue load limit often controls near the contraflexure for bending inflection along continuous spans (Nolan S, Perez J, Hartman D, Ellis K, 2019, Bakers haulover cut bridge: seawall-bulkhead rehabilitation and new GFRP-RC solutions, Transportation research board, paper 19-05552R1, Washington DC, January 2019, pp 7–8). The AASHTO LRFD “Design Guide Specification for GFRP-Reinforced Concrete Bridge Decks and Traffic Railings” (BDGS-1) was recently expanded to include all RC members under the 2nd edition (BDGS-2). As part of the BDGS-2 specifications, owners may require manufacturers to certify that their products meet endurance limits based on testing, if they propose using a higher limit (AASHTO, 2018, LRFD bridge design guide specification for GFRP reinforced concrete, 2nd edn., AASHTO committee bridges and structures, December 2018, Burlington, VT.). The ASTM D7957-17 “Standard Specification for Solid Round Glass Fiber Reinforced Polymer Bars for Concrete Reinforcement” (ASTM International, 2017, Standard specification for solid round GFRP bars for concrete reinforcement, ASTM D7957/D7957M-17. July 2017, West Conshohocken, PA) does not provide test methods or acceptance criteria for creep rupture or cyclic fatigue. Industrywide endurance limit characterization curves would allow manufacturers to assure that a product meets the established limits through simple short duration verification testing. Refinements in endurance design limit should be linked to creep rupture at 75, 100, and a maximum time up to 150-year service life, or based on fatigue at 2, 3, or 4 million cycles, as appropriate for GFRP-RC bridge design specification and consistent with pending AASHTO Service Life Design Guide expectations proposed in the NCHRP project 12–108 (NCHRP, 2019, Guide specification for the service life design of highway bridges: project 12–108”, Modjesky & Masters for National Cooperative Highway Research Program, October 2019, Washington DC). This paper shares testing of improved GFRP rebar conforming to ASTM D7957-17 specification, using a corrosion resistant vinyl ester resin with corrosion reistant E-CR glass at higher fiber content, enabling a 60 GPa tensile elastic modulus that safely resists higher sustained load.KeywordsGFRPReinforced concreteDesign factorDurabilityCorrosion resistanceInfrastructure