Concrete has a great impact on the environment due to its carbon footprint. Concrete floor slabs generally contribute to more than half of the structural mass of a multi-story building. These slabs are commonly constructed as solid structures, not due to the structural efficiency, but rather the inexpensive planar formwork that is used to cast them. In order to reduce the concrete volume of these floor slabs, the members of the RIBB3D project sought out unconventional design- and production methods for floor slabs, while complying with building code regulations.
The E25 robot extruder solution
“Using computational design tools, we came up with a ribbed topology for the design of the floor slab.” says Joris Burger, PhD Researcher, Gramazio Kohler Research at ETH Zurich.. “The slab formwork was created with 3D printing using the E25 thermoplastic pellet extruder on an industrial robot.” he continues. .. “3D printing formwork allows the production of complex designs that would not be feasible to produce using other formworking methods”.
Stiffeners can be incorporated into the formwork design, which help to withstand the pressure of the fresh cast concrete. Steel reinforcement cages are placed at the ribs after which the formwork is closed by using robotic non-planar printing. The ribs can then be cast with standard self-compacting concrete. “Because we printed the formwork for the ribs up-side down, we could easily cast the flat part of the slab after demoulding, using conventional formwork” adds Burger.
3D Printing of formwork has the potential to enable material-efficient concrete structures, due to the increased geometrical freedom it can bring.
The result showed an optimised ribbed floor slab design that reduces the use of concrete by around 40%. Measurements showed that compared to a reference solid slab, the optimised design with ribsslabs reached an 80% higher ultimate load using conventional concrete. When low-carbon concrete would be used, the carbon footprint can be reduced by roughly two thirds. The ribbed slabs fulfilled all requirements in terms of structural integrity, comfort and robustness. “This collaborative project highlights the potential of using 3D printing in the creation of optimised concrete ribbed slabs, paving the way towards sustainable concrete construction.”