Bending and Pull-Out Tests on a Novel Screw Type Reinforcement for Extrusion-Based 3D Printed Concrete

The lack of available reinforcement methods suitable for extrusion-based 3D concrete printing is well known. Because conventional methods using pre-placed steel bars are incompatible with this manufacturing method, several alternatives are under development. This paper introduces a novel reinforcement application method, based on screwing. Contrary to placement methods based on pushing, i.e. only a translational movement, the combination of translation and rotation inherent in the screwing motion, allows a practically void-free mechanical interlock with which a high level of bond can be attained. The concept makes use of the fact that the print mortar is still highly pliant for some time after deposition, allowing screws to be inserted without fracturing the concrete. The translational-rotational movement needs to be externally controlled, as the material at the early age does not provide sufficient resistance to pull in the screw on application of the rotation. Pull-out tests from printed and cast samples and 3-point bending tests on printed specimens showed a high bond strength and thus underline the feasibility of this concept