Behaviors of hybrid beams composed of seawater sea-sand concrete (SWSSC) and a prefabricated UHPC shell reinforced with FRP bars

The primary objective of this study was to develop a new type of hybrid beam with excellent durability. This new type of beam was designed to be suitable for rapid in-situ construction in an offshore environment. It composed of seawater sea-sand concrete (SWSSC) and a prefabricated ultrahigh performance concrete (UHPC) shell, and was reinforced with basalt FRP (BFRP) bars or steel-FRP composite bars (SFCBs). Two types of production methods for the UHPC shell were designed and compared. The main objective was to test the mechanical properties of the proposed hybrid beams and to verify the feasibility of the proposed preparation processes. Traditional monotonic four-point bending test methods and 3D digital image correlation (DIC) measurements were performed simultaneously. The test results showed that the shear cracks reduced significantly due to the existence of UHPC shell. Because the depths of the UHPC sidewalls were ¾ of the beam depth, the bending strength of the test beam was not substantially improved, but the cracking load and energy absorption improved by approximately 70% and 24%, respectively. The integrity of the hybrid beam prepared by the rotation method was better than that of the hybrid beam prepared with a prefabricated U-shaped UHPC shell.