Concrete is responsible for 8% of our global carbon footprint. Now more than ever, it is imperative to use concrete more efficiently. With optimisation algorithms, we can design complex buildings that use less than half the amount of concrete. Still, we are limited by the available fabrication technologies: the conventional formwork solutions only allow us to build predefined geometries with limited customisability.

To tackle this problem, we propose an automated solution that combines the fabrication speed of concrete 3D printing and the geometric precision of reusable 3D printed formwork. We demonstrated this method with a highly optimised post-tensioned structural slab prototype.

To make this possible, we developed an innovative process that allows us to dynamically control the setting rate of the 3D printed concrete. This digital control over material properties means we can extrude a fluid concrete that emulates the complex surface of the formwork perfectly, and a fast setting concrete that does not need any additional formwork for the upper structure.

The proposed method allows the implementation of radically new aesthetics in slabs with functional features on both sides. Moreover, the method involves less digital fabrication processes, requires less manual labour, and is more resource-efficient in comparison to the state of the art fabrication alternatives for bespoke slabs. Based on these considerations, the method aims to facilitate a more diverse repertoire of contextualised design solutions in real buildings.