Hybrid reinforcement and engineered cementitious composite (ECC) layering effects on the flexural capacity of concrete beams

Abstract To address the issue of steel corrosion, fiber-reinforced polymer (FRP) bars, particularly glass fiber-reinforced polymer (GFRP) bars, have been increasingly employed as alternatives to steel rebars in various applications. However, GFRP exhibits a reduced elastic modulus compared to steel rebars. GFRP demonstrates a linearly elastic behavior till failure, indicating that it is a brittle material. To overcome such disadvantages, engineered cementitious composite (ECC) concrete that has a high ductility can be used instead of traditional concrete in tension region. In this paper, nine partial ECC beams, reinforced either solely with GFRP bars or with a GFRP-steel bars hybrid configuration, were designed and experimentally evaluated to examine their flexural performance. In order to provide a composed beam with excellent serviceability, ECC concrete was used in key parts inside the tension zone. The primary variables examined in this research included the type of reinforcement used, ECC configurations either in a U-shaped form work or as a bottom layer only, ECC bottom layer thickness in tension, and the influence of incorporating GFRP bars on the flexural performance. Beams were tested under four-point bending to evaluate failure modes, cracks distribution, load capacity, deflection, and crack width. The experimental findings indicated that the observed failure mode aligned with the intended design failure mode. The data obtained for cracking, yielding, and ultimate capacity showed a good agreement with proposed models and codes equations. The deflection and crack width of hybrid-reinforced concrete (RC) beams were less than GFRP-RC beams. The proposed U-shaped ECC form work had a significant effect in increasing the distribution of vertical cracks, minimizing the mean distance between adjacent cracks, and reducing the measured crack width by 40%. In addition, increasing the thickness of ECC layer in tension area or adding side ECC concrete led to an increase in the distribution of vertical cracks, decreasing in the measured crack width, and had a slightly effect on deflection and load capacity. Finally, increasing the ratio of GFRP bars to steel bars (A f /A s ) increased the deflection, while the measured crack width almost has the same value due to the existing of ECC concrete layer.