ETH Zurich Uses 3D Printed Forms to Build Yummy Waffle Slabs

In a Nervi move, an expensive and labor-intensive system is brought into the 21st century.

portion of slab

Patrick Bedarf/DBT

Every March 25th, on Våffeldagen or Swedish Waffle Day, we wax eloquent about the wonders of waffle slabs, which allow much longer spans with much less concrete and look beautiful and yummy all on their own without covering them up with drywall.

The world's yummiest waffles were cooked up by Italian engineer Pier Luigi Nervi, who built the Gatti Wool Factory in 1951 using an isostatic line tool that he patented, doing all the calculations and drawings by hand, with craftspeople then building all those boxes. It's no wonder this isn't done much anymore; it was really labor-intensive to build that formwork and it's much cheaper today to just pour a flat slab and use more concrete.

But now, in a Nervi move, architect Patrick Bedarf and his team at ETH Zurich Digital Building Technology (DBT) bring yummy waffle slabs into the 21st century by trading in the formwork for "FoamWork." According to DBT:

completed slab

Patrick Bedarf/DBT

"Building geometrically complex formwork for concrete elements that are optimized for resource-efficiency is often wasteful and labor intensive. FoamWork explores how foam 3D printing (F3DP) can be used to produce unique shapes for functional stay-in-place or temporary and recyclable formwork in concrete casting. The resulting mineral composite elements can save up to 70% concrete, are lighter, and feature improved insulation properties. The printable mineral foams based on recycled waste are developed at ETH Zürich in collaboration with FenX AG."

In a study, "The Ribbed Floor Slab Systems of Pier Luigi Nervi," the authors explain how Nervi used theoretical calculations to design his ribs: "The method includes theoretically calculating the principal bending moment directions at a selection of nodes, hand drawing lines at set lengths in the respective directions, recalculating the directions at the next nodes, repeating the process until reaching a boundary." Then they have to bang up all the forms, carefully place reinforcing in the bottom between them, and then pour the concrete.

placing foamwork
Placing FoamWork.

Patrick Bedarf/DBT

The marvel of the DBT is that they can design it all on the computer, send it off to the robot, and then about the only thing humans have to do is place the light foam form components and fill it with ultra-high-performance fiber-reinforced concrete (UHPFRC). They can leave the foam in place for insulation or remove it so that we can all admire the slab. They note at DBT:

Robot that makes the foam

ETH Zurich

"This novel fabrication approach is envisioned to significantly impact the responsible and sustainable consumption of resources and energy in the building industry. It enables the manufacturing of geometrically complex foam elements that were previously unfeasible and wasteful to produce with conventional methods. The foam shapes produced with F3DP can be used as stay-in-place applications or removed and recycled for printing the next formwork."

Nervi designed some of the most beautiful concrete structures ever built, but they were also incredibly efficient, covering huge spans using very little material. We have also noted many times that one of the radical rules of design today is to use as little material as possible, whatever it is, and this technology does exactly that.

slab on edge

Patrick Bedarf/DBT

If you going to build with concrete, why not bring back the waffle slab, use 70% less of the stuff, make it beautiful, almost biophilic in the way it looks tree-like, and leave it exposed instead of adding more stuff like drywall to cover it? This is such remarkable technology that makes it all possible—it makes me want to celebrate Waffle Day a few months early.