Physical Properties, Longitudinal Tensile Properties, and Bond Strength of the New Generation of GFRP Bars

This paper presents an experimental study that investigated the physical properties, longitudinal tensile properties, and bond strength of a new generation of glass fiber-reinforced polymer (GFRP) bars. Five commercially available types of GFRP bars with different surface treatments (deformed/ribbed, helically deformed, helically grooved, double helical wrap/sand-coated, and sand-coated) were selected for this investigation. Two bar sizes (No. 5 and No. 8)-with 15.9 and 25.4 mm nominal diameters representing the range of GFRP-reinforcing bars typically used in practice as longitudinal reinforcement in concrete flexural members-were selected from each of the manufacturers. The test results reveal that these new higher modulus GFRP bars have physical properties, tensile strength, and moduli of elasticity greatly exceeding the requirements of ASTM and Canadian Standards Association (CSA) standards. The GFRP bars had measured cross-sectional areas near or slightly over the maximum cross-sectional area allowed by ASTM standards. The mechanical properties reported in this study were based on nominal cross-sectional areas. The longitudinal tensile properties and bond strength of the GFRP bars satisfied the limits in ASTM and CSA standards. GFRP bar manufacturers have developed and are producing GFRP bars with guaranteed strengths that significantly exceed the ASTM minimum specifications. However, ASTM bases qualification methods for tensile strength on the minimum ASTM specified values, which could differ from the values implemented in the design. Until ASTM bases rejection on the strength used in design, the designer should add rejection criteria to the project specifications to ensure that GFRP bar acceptance is based on the strength assumed for design, which could be between the minimum value specified in ASTM and the manufacturer's guaranteed value.