
With concrete the most utilized construction material on Earth, the drive to find more efficient methods drives engineering and architecture researchers worldwide forward. According to an announcement from ETH Zurich, research from an architecture PhD student shows that a new type of formwork to shape a floor can potentially use up to 60 percent less concrete and 90 percent less steel than conventional reinforced concrete floor slabs - further reducing construction's carbon emissions and material waste.
Led by ETH Professor Philippe Block', one of the Block Research Group's (BRG) innovations involves a vaulted floor element made of concrete. According to the announcement, "Through clever geometry, these floors achieve much thinner sections than their conventional counterparts and do not require any embedded steel reinforcement. The technology is being commercialized through VAULTED AG, a spinoff from ETH.
Non-standard Floors; Non-standard Forms
Four individual parts are joined to create the formwork, which has the capacity to hold up to a tonne of concrete. The concrete is poured directly onto the formwork. Once it has cured, the formwork can be removed from underneath.ETH Zurich
Per the announcement:
Unfold Form consists of thin, flexible plywood strips that are connected by textile hinges and can be unfolded like a fan. Four of these compact units can be rapidly assembled within a wooden frame to create a sturdy, zigzag shaped mould onto which concrete can be poured directly.
After the concrete cures, the formwork can be easily detached from underneath, folded away and stored for its next use. While the system used for the prototype weighs just 24 kilogrammes (52.9 lbs.), it is can support up to a tonne of concrete.
“I was looking for a solution that would allow me to use strength through geometry not only to optimise the final structure but also the formwork itself,” says Lotte Scheder-Bieschin. “This approach reduces material usage and makes the entire process more environmentally friendly.” The formwork’s distinctive geometric structure allows for reductions of up to 60 percent in concrete and 90 percent in reinforcement steel.
Architecture PhD student Lotte Scheder-Bieschin created this vaulted floor in unreinforced concrete using her innovative formwork system.ETH Zurich
“The Unfold Form formwork can be produced and assembled without specialised knowledge or high-tech equipment,” notes Scheder-Bieschin. One of her aims was to create a simple and robust system that could be used worldwide, even with limited resources. Currently, formwork for non-standard concrete shapes typically requires digital fabrication. “This creates barriers for sustainable concrete construction in developing countries, where the need for new buildings is especially high,” she says.
The formwork can be produced cheaply. “The only things needed in addition to the materials are a template for the shape and a stapler,” adds Scheder-Bieschin. The materials for the prototype cost only 650 Swiss francs in total.
The individual components are light and compact enough to transport easily. Scheder-Bieschin demonstrated the system's simplicity by assembling it herself during her pregnancy. “I wanted to ensure my design was simple enough for anyone to build, regardless of their circumstances,” she says.
Zigzag Ridges Like Seashells
How does this innovative formwork achieve both lightness and stability? During development, Scheder-Bieschin applied her expertise in bending-active structures – a topic she had worked on during her studies. This technique involves bending elastic materials like thin and long splines or plates of wood, where the resulting deformation creates stability and allows for curved, lightweight structures.
A key feature of Unfold Form is the zigzag-like arrangement of wooden strips. “This ribbing provides additional stiffness without significantly increasing the overall weight,” explains Scheder-Bieschin. “You can find such articulated structures in nature, like in seashells.”
The zigzag pattern strengthens both the formwork and the concrete poured onto it: “The concrete incorporates this design into a structural rib pattern, which assist in load transfer.”
Strength Through Curvature
The interaction between the individual strips is crucial for the formwork’s stability, Scheder-Bieschin explains: “When you bend a single strip or plate, it becomes very wobbly when loaded, and it's difficult to control which shape the board will bend into.” However, when you connect two strips along a curved edge, you achieve much higher rigidity. “Under load, the strips deform minimally, and you can control the final shape via the design of these connection curves,” she says. This technique, called curved-crease folding (CCF), has been around for some time and draws its inspiration from the art of origami.
Folding in general consistently progresses from larger to smaller sizes, beginning with a flat element that is gradually reduced through the folding process. This makes the folding technique unsuitable for use in construction. “Consider a vaulted concrete floor measuring two by three metres – the starting plate would need to be approximately three by five metres. From a transport perspective, this is of course highly impractical,” Scheder-Bieschin points out.
From Paper Model to Concrete Prototype
Scheder-Bieschin was intrigued by the challenge of adapting this simple but ingenious CCF system for architectural purposes. She experimented with paper models at her desk, eventually devising a system that she calls curved-crease unfolding: “At some point, I started gluing the pieces together differently. And that's how I found a system that starts out as a stacked shape that can be fanned out – just like a hand fan. And at the same time, the curved shape is achieved.”
The next challenge was to move from a thin sheet of paper to a structural material of a certain thickness. The doctoral student solved this tricky problem with the help of textile hinges.
She then developed a computer method for the simulation. “The initial prototypes already validated my concept,” she recalls. “Using simple 2D prefabrication, I could create folded, compact panels that unfold easily and have the required rigidity to support concrete.”
A sustainable final product: Through clever geometry, these vaulted floors achieve much thinner sections than their conventional counterparts and do not require any embedded steel reinforcement.ETH Zurich
Real-life Test in South Africa
In addition to the final 3-by-1.8-metre prototype, which is located in the Robotic Fabrication Laboratory (RFL) on the Hönggerberg campus, a twin concrete structure also exists in South Africa. It was built using the same formwork. Mark Hellrich, a scientific assistant and contributor to the Unfold Form project, transported the folded formwork to Cape Town using two surfboard bags. Working together with nonCrete, a local firm dedicated to sustainable construction and affordable housing solutions, they cast the second prototype.
This demonstrated three things at once: The formwork system can be reused without any loss of quality, it is easy to transport, and it works with different types of concrete. NonCrete used its bio-concrete based on shredded invasive vegetation from the area. “This shows that premium-grade concrete isn't necessary for creating sturdy floors with the new formwork,” Scheder-Bieschin notes.
She says that the South African partner company was impressed by the results: “The goal is to use this innovative formwork system to construct high-quality, dignified and sustainable housing in South African townships.”
After completing her doctorate in a few months, the researcher will continue developing her technique as a postdoc at ETH Zurich, with plans to bring her product to market. Currently, the 33-year-old is working on the design for a market hall in a Cape Town township using her formwork system. The next step, however, is primarily about helping people help themselves: “We are planning training programs for the locals so they can build the formwork and the buildings on their own.”
More information on the research can be found at https://brg.ethz.ch/research/prototypes/838.