ARCS: Automated Robotic Concrete Spraying for the Fabrication of Variable Thickness Doubly Curved Shells

The fabrication of doubly curved concrete shells traditionally poses challenges in terms of material deposition and formwork manufacturing. Recent advances in digital fabrication techniques including robotics in construction have created tools to better tackle these challenges. We present a digital fabrication system to accurately deposit cementitious materials onto doubly curved surfaces using robotic concrete spraying in a process for prefabrication of structural shell components we call ARCS (Automated Robotic Concrete Spraying). Using inputs of a generic variable thickness shell volume, a robotic path is generated to deposit material onto the formwork surface where required. Paths are generated on the surface using geodesic lines as guides in order to create iso-curves for evenly spaced spray paths. Additionally, layers are incrementally deposited to allow for variable thicknesses across the surface. This approach is flexible enough such that additional features can be embedded onto the shell such as ribs. We demonstrate this automated fabrication process on a 1.8 m by 1.8 m scale shell specimen.