Characterization and Performance Evaluation of Large-Diameter GFRP Bars

This study presents a material characterization of large-diameter 36-mm (No. 11) glass fiber–reinforced polymer (GFRP) reinforcing bars produced by two manufacturers, referred to as Type A (sand-coated) and Type B (deformed ribbed). With the expanding use of GFRP bars in concrete infrastructure and the recent investments, an urgent need has emerged to validate the performance of larger bar sizes and the initial provisions proposed in the Florida Department of Transportation (FDOT) specifications, which are not yet explicitly covered in existing ASTM and AASHTO specifications. A series of standardized tests were performed to evaluate key properties, including fiber content, glass transition temperature, degree of cure, cross-sectional area, tensile strength and modulus, transverse and horizontal shear strength, and bond strength. Results revealed that both bar types met most expanded FDOT performance criteria. The study also discusses how surface treatments and manufacturing variations affect bar performance. Recommendations are provided for revised provisions for 36M (No. 11) bars in FDOT specifications and manufacturer qualification requirements, plus consideration for addition to ASTM material specifications, including proposed updates to allowable tolerances, strength thresholds, and testing protocols.