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 fiber reinforcement that can improve the behavior of structural elements thanks to its high strength and improved ductility properties. The mix design that provides these superior properties of UHPC also makes it a high-cost material. For this reason, the use of UHPC in parts where it contributes more significantly to the performance of the structural elements will lower down the costs and reduce the negative environmental effects 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 producing mini-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-UHPC composite beams, the mixtures should have different rheological properties depending on the order of the layers. Increasing the total thickness of the UHPC layer enhanced the initial and yield stiffnesses as well as the peak loads. UHPC layer with thicknesses of 15 mm in tension zone, 30 mm in tension zone, and 15+15 mm in tension+compression zone led to the load-carrying capacity increment ratios of 20%, 34.6%, and 24.3%, 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 the tensile reinforcement ratio in UHPC layers can overcome the drawbacks in the ductility.

Hybrid Interfacial Transition Zone between Wet—On—Wet Casted Concrete—Microstructure and Mechanical Properties

“…since increasing the loading carrying capacity of the hybrid beam. Yalcinkaya [ 24 ] concluded that increasing the thickness of the UHPC layer from 15 mm to 30 mm in the tension zone led to the load–carrying capacity increment ratio of 20% and 34.6% respectively for the hybrid concrete (UHPC-NC) layered horizontally.…”

“…The arrangement of the layers and the thickness of the bottom layer affected the flexural strength of the hybrid concrete. Yalçınkaya [ 24 ] investigated the combination of the UHPC with a steel reinforcement with normal mortar (NM) and self–compacting mortar (SCM)which resulted in higher load carrying capacity. The interface of these hybrid concretes did not sustain any damage.…”

Theoretical and Experimental Investigation on the Flexural Behaviour of Prestressed NC-UHPC Composite Beams

“…The tensile properties at the edge of the tensile zone of prestressed members are generally composed of two parts: the compressive stress caused by prestressing and the tensile strength of the concrete material [ 15 ]. The ultimate tensile strength of the UHPC structure at the edge of the tensile zone is calculated according to Equation (13).…”

“…In recent years, a considerable amount of experimental research has been undertaken on the flexural behavior of NC-UHPC composite beams, including that reported in [ 14 , 15 , 16 , 17 , 18 ]. In [ 14 ], the bond strength between UHPC and NC was found to be very high.…”

“…Failure occurred when the concrete was crushed at the NC layer [ 14 ]. The initial and yield stiffnesses, as well as the peak and ultimate loads, were found to be enhanced by increasing the thickness of the UHPC layer, enabling expression of its high strength and ductility characteristics [ 15 ]. Compared with an NC beam, the numbers of cracks in a UHPC-NC composite beam was found to be significantly reduced [ 16 ].…”