Toolpath-Driven Surface Articulation for Wax Formwork Technology in the Production of Thin-Shell, Robotic, CO2-Reduced Shotcrete Elements

This study introduces a digital fabrication process for producing recyclable, closed-loop wax formwork for architectural concrete applications with visually rich surface articulation while drastically reducing formwork milling time. As such, this paper presents (a) a circular large-scale production method for wax blocks via a single casting process; (b) four machine-time-optimized surface articulation strategies through CNC toolpath-driven design; (c) the investigation of different coating systems to improve architectural concrete surface quality and to ease demolding; and (d) the integration of robotic concrete shotcreting using a low-CO₂ fine-grain concrete. For the first time, wax formwork technology, characterized by its waste-free approach, has been combined with robotic shotcreting in a digital and automated workflow to fabricate fiber-reinforced, geometrically complex thin-shell concrete elements with distinct surface articulations. To evaluate the process, a series of four thin-shell concrete elements was produced, employing four distinct parametric toolpath-driven designs: linear surface articulation, crossed surface articulation, topology-adapted curve flow surface articulation, and robotic drill topology-adapted surface articulation. Results revealed a possible reduction in milling time of between 77% and 94% compared to traditional milling methods. The optimized toolpaths and design-driven milling strategies achieved a high degree of visual richness, showcasing the potential of this integrated approach for the production of high-quality architectural concrete elements.