Sustainable Production of Complex Precast Concrete Elements Without Demolding Drafts Using Concrete Extrusion and Processing

The paper presents the sustainable production of flexible and recyclable formwork elements. The models are produced by means of extrusion and processing concrete in a fresh and hardened state. The model milled to target dimensions enables resource-efficient molding with various casting resins. The combination with conventional formwork elements enables the production and simple demolding of complex concrete elements without demolding drafts or with local undercuts. A clinker-reduced concrete mixture with a lower CO₂ footprint than conventional concrete mixtures for 3D printing has been developed as part of the research. The extrusion and machining programs are created using Grasshopper, a visual programming environment used as an extension to Rhinoceros CAD software to create parametric geometries. This enables programming for planning the paths and controlling the 6-axis industrial KUKA robots. The extruded and processed formwork elements can be recycled. The material can be fed back into the printing process without negatively affecting the rheological and mechanical parameters of the concrete. The resulting material cycle is the key to the efficient and sustainable production of precast concrete products.