Testing 3D printed reinforced concrete beams

3D printing of concrete (3DPC) is developing at a rapid pace in the construction industry. At this moment, most of the 3DPC structural elements are made of plain unreinforced concrete. Pursuing the idea to improve its structural performance, the reinforcing possibilities for 3DPC are under thorough investigation. Simultaneous reinforcement of 3DPC structural elements during printing process includes several main directions: additive-based, allowing incorporation of thin steel and polymer fibres to the concrete mixture; integration of fibre reinforced polymer threads along the extruded layers enhancing the ultimate strength solely in the direction of the threads; manual and time-consuming installation of staples and clamps. Together with that, due to the layered extrusion process, implying fast concrete curing and excluding compacting, the material has another behaviour than ordinary concrete. At present, the authors are developing an innovative technological concept for digital integration of reinforcement during concrete printing. The idea is to use conventional steel rebars in structural members allowing the continuity of reinforcement across interlayer interfaces. In order to prove the feasibility of this approach, the structural performance of concrete beams produced from the mortar used for 3DPC, and reinforced with steel rebars was investigated empirically. The parameters influencing the beam behaviour and failure modes were described. These include the interface bond between steel and mortar, material strength, which is a time-dependant variable when considering fast curing layer-by-layer production and hardening; the interface quality between the concrete layer and steel rebars; the anchorage features. Based on an experimental study on medium size beams (700 mm long), the bending and interface shear failure in 3D printed RC beams, including the anchorage effects are described in detail in this paper. Several beam dimensions and reinforcement configurations have been tested in a repetitive way and their deformation measured using Digital Image Correlation technique.