CRUX

CRUX is a UHPC structure with a minimal-surface geometry. On this project, BAT, Hyundai Engineering and Sampyo Cement R&D Center applied robotic fabrication techniques to test a new construction method for free-form concrete structures.

To cast a free-form concrete structure measuring approximately 2 × 5 × 3 m, we built low-cost formwork from EPS instead of the metal typically used for free-form formwork. The complete formwork system was planned as 10–12 segments suited to the assembly process, and these segments were in turn divided into 170 pieces sized to standard EPS blocks (1.8 × 0.9 × 0.6 m). The EPS pieces were machined by robotic milling, and every face was machined — including the curved surfaces and the flat faces where pieces meet — to reduce errors during bonding. After 3D scanning verified the accuracy of the pre-assembled segments, the curved surfaces were given a final paint coating.

Instead of bending rebar to follow the curved surfaces of the structure and tying the bars together, we applied a metal 3D printing technique known as wire-arc additive manufacturing (WAAM). This made it possible to fabricate a precisely shaped rebar mesh and embed it at the center of a relatively thin, 50 mm curved concrete shell.