Dynamic 3D print head for spatial strand extrusion of fiber-reinforced concrete: requirements, development and application

Abstract

Abstract Additive manufacturing is gaining more significance in architecture and construction due to a shortage of skilled workers, resource scarcity and increasing design requirements. Over the past years, approaches for layer-wise and spatial extrusion of concrete were developed for automated, formwork free and complex concrete processing. The spatial concrete extrusion is possible due to an inert support suspension that stabilizes the strands during hydration. The process is capable for unlimited overhangs, increasing printing speed and ultra-lightweight concrete structures. Even though, for filigree and spatial framework structure, its application is highly impaired by the anisotropic strength and brittle concrete behavior requiring reinforcements. In following research, the use of fiber-reinforced concrete is investigated for spatial concrete extrusion. Compared to unreinforced concrete, fibers improve the tensile strength and ductility and can be obtained from recyclable sources. Since its structural effect is dependent on their orientation in the matrix, its processing requires a controlled extrusion and high flexibility of nozzle rotation. Therefore, a print head was developed that increases the rotation freedom of a nozzle without harming its robot reachability to improve additive manufacturing of fiber-reinforced concrete strands. This paper concludes investigations of fiber orientation in extruded strands depending on nozzle alignment, a concept and prototype of a dynamic 3D print head, which is capable of 3D rotations, and applications for filigree 3D structures, which demonstrate new possibilities for fiber-reinforced materials.