Experimental Study on the Flexural Performance of GFRP-Reinforced Concrete Beams with a Prefabricated Permanent UHPC Formwork

The flexural performance of concrete beams incorporating glass fiber–reinforced polymer (GFRP) bars and further strengthened by a prefabricated permanent ultrahigh-performance concrete (UHPC) formwork is investigated in this study. A total of eight beams, including seven composite beams with a UHPC formwork and one reference beam without a UHPC formwork, were tested under four-point bending. The parameters evaluated included the interface treatment method, the existence of a prefabricated permanent UHPC formwork, the presence of a top UHPC layer, and the GFRP reinforcement ratio. Experimental results revealed that the flexural capacity of beams with the UHPC formwork significantly improved relative to the reference beam. The maximum crack width of the composite beam was smaller than that of the reference beam under the same load. The addition of the top UHPC layer significantly increased the ultimate load of the composite beam, and the high tensile strength of the GFRP bar was effectively utilized. Moreover, characterization results revealed that interface treatment, specifically the addition of a linear low-density polyethylene bubble wrap interface, prevented debonding of the UHPC formwork from the concrete. A calculation model for flexural stiffness was also developed, which provided high predictive accuracy as verified by the close agreement of its results with experimental measurements.