Additive Manufacturing of Topology-Optimized Lightweight Slabs Using Foam Concrete (2025-10)¶

In order to address the major global challenges ofclimate change, material scarcity and the continuously rising demand for living space, there is a need to develop sustainable building components with optimized material use that can be mass produced. Concrete structures, with their high volume and weight, offer great potential for optimization towards lightweight structures. The additivemanufacturing of structures with advanced robotics enables free-form material placement, though its current application is predominantly limited to the deposition of load-bearing material ("positive 3D printing"). Recent research has focused on improving the bond strength between individual layers and between the printed material and the embedded reinforcement. This paper presents an alternative approach that utilizes pumpable foam concrete as robotically manufactured displacement bodies for the production of topology optimized slabs ("negative 3D printing"). For the production of these displacement bodies, the form is placed as shaping frame using a 3D-printable foam concrete 3DPFC and is then filled with an ultra-lightweight foam concrete ULFC. The developed 3DPFC exhibits high stability in the fresh state and has approximately 69 % (≈ 1650 kg/m³) of the density of concrete (2400 kg/m³). In addition to its potential for topology optimization, the utilization of foam concrete offers sustainability advantages over conventional plastic displacement bodies, as this new slab is made exclusively ofmineral materials and is therefore fully recyclable. The top and bottom of the slab, as well as the topology optimized ribs in between, are cast and reinforced with nonmetallic reinforcement. The paper focuses on the structural capacity of this lightweight slab and the manufacturing process.