Experimental Investigation of Hybrid Beams Utilizing Ultra-High Performance Concrete (UHPC) as Tension Reinforcement.

Ultra-high performance concrete (UHPC) is a new generation concrete with extremely high tensile and compressive strength, high durability, and ductility. UHPC offers tremendous opportunities for use in new thin and slender structural concrete elements and repair of existing concrete structures and has an excellent potential to replace conventional steel reinforcement in normal concrete (NC) members. This paper investigated the potential application of a hybrid NC-UHPC beam using a thin UHPC layer on the tension face to cater to tensile stresses, eliminating the need for passive steel reinforcement. Four-point flexural load tests were performed on 24 composite beams with a thin UHPC layer overlaid with NC. The parameters considered include the thickness of the UHPC layer, depth, and span of the beam. A linear behavior categorizes the flexural behavior of the hybrid NC-UHPC beam up to the ultimate load, after which the hybrid beam shows a non-brittle failure, and softening ensues associated with cracking, increased deflection, and loss of load resisting capacity. The unfinished top surface of the UHPC layer and the overlying NC developed a full composite action without any slip. It was found that a two-day self-curing of the UHPC layer was found to be essential for the development of a strong bond between the layers. The random dispersion and orientation of steel fibers in the UHPC can lead to a decreased tensile response for larger hybrid NC-UHPC beams. The experimental results validate the potential of hybrid NC-UHPC beams as an attractive, structurally feasible, and alternative sound form of construction in terms of their high flexural strength and corrosion-free service life. The proposed unreinforced hybrid system could be used in the construction of precast beams and slabs for residential as well as industrial buildings. Further research, including full-scale load testing of the hybrid beam, is needed prior to practical applications.