Experimental verification and theoretical predictions of crack widths in concrete beams reinforced with glass fiber reinforced polymers

Abstract

This paper presents an experimental study of the flexural behavior and crack development of concrete beams reinforced with three types of longitudinal Glass Fiber Reinforced Polymers (GFRP) reinforcement: sand-coated GFRP, helically-wrapped GFRP, and conventional steel bars. Sixteen beams without shear reinforcement were tested under four-point bending, with crack widths measured at four load levels. The study evaluated the influence of reinforcement type, surface treatment, and reinforcement ratio (ρ_s) on crack width development and structural capacity. Increasing ρ_s led to higher resistance and smaller crack widths in all reinforcement types. Sand-coated GFRP provided the best crack control and the highest strength due to superior bond, while helically-wrapped GFRP showed larger cracks and lower capacity despite a similar reinforcement ratio. Steel-reinforced beams exhibited the most ductile behavior and moderate crack widths. Theoretical predictions according to EN 1992-1-1, ACI 440.1R, and CSA S806 were compared to experimental results, with Eurocode providing the best overall match, and at service load levels, ACI and CSA were the most consistent ones for sand-coated and helically-wrapped GFRP-reinforced beams, respectively. These findings provide critical, data-driven guidance for structural engineers, confirming that sand-coated GFRP bars are essential for reliable crack control and validating EN 1992-1-1 as a safe and accurate tool for serviceability design.