A preliminary study on the development of the normal concrete-UHPC composite beam via wet casting

Abstract

Ultra-high-performance concrete (UHPC) is an innovative cementitious composite containing steel fiberreinforcement that can improve the behavior of structural elements thanks to its high strength and improvedductility properties. The mix design that provides these superior properties of UHPC also makes it a highcostmaterial. For this reason, the use of UHPC in parts where it contributes more significantly to theperformance of the structural elements will lower down the costs and reduce the negative environmentaleffects caused by high cement content. In this preliminary study, the production of normal concrete (NC)-UHPC reinforced concrete (RC) composite beams by wet-on-wet casting was investigated by producingmini-RC beams. In the production of mini-RC beams, normal mortar (NM) and self-compacting mortar(SCM) mixtures were used to represent an NC. The results showed that in the production of NC-UHPCcomposite beams, the mixtures should have different rheological properties depending on the order of thelayers. Increasing the total thickness of the UHPC layer enhanced the initial and yield stiffnesses as well asthe peak loads. UHPC layer with thicknesses of 15 mm in tension zone, 30 mm in tension zone, and 15+15mm in tension+compression zone led to the load-carrying capacity increment ratios of 20%, 34.6%, and24.3%, respectively. However, increasing the thickness of the UHPC layer in the composite beams,especially more than 15 mm, reduced the ductility ratio and energy absorption capacity. Optimizing thetensile reinforcement ratio in UHPC layers can overcome the drawbacks in the ductility.