How good old mud can lower building costs

Buildings cost a lot these days. But when concrete buildings are being constructed, there’s another material that can make them less expensive: mud.

MIT researchers have developed a method to use lightly treated mud, including soil from a building site, as the “formwork” molds into which concrete is poured. The technique deploys 3D printing and can replace the more costly method of building elaborate wood formworks for concrete construction.

“What we’ve demonstrated is that we can essentially take the ground we’re standing on, or waste soil from a construction site, and transform it into accurate, highly complex, and flexible formwork for customized concrete structures,” says Sandy Curth, a PhD candidate in MIT’s Department of Architecture who has helped spearhead the project.

The approach could help concrete-based construction take place more quickly and efficiently. It could also reduce costs and carbon emissions.

“It has the potential for immediate impact and doesn’t require changing the nature of the construction industry,” says Curth, who doubles as director of the Programmable Mud Initiative.

Curth has co-authored multiple papers about the method, most recently, “EarthWorks: Zero waste 3D printed earthen formwork for shape-optimized, reinforced concrete construction,” published in the journal Construction and Building Materials. Curth wrote that paper with nine co-authors, including Natalie Pearl, Emily Wissemann, Tim Cousin, Latifa Alkhayat, Vincent Jackow, Keith Lee, and Oliver Moldow, all MIT students; and Mohamed Ismail of the University of Virginia.

The paper’s final two co-authors are Lawrence Sass, professor and chair of the Computation Group in MIT’s Department of Architecture, and Caitlin Mueller, an associate professor at MIT in the Department of Architecture and the Department of Civil and Environmental Engineering. Sass is Curth’s graduate advisor.

Building a structure once, not twice

Constructing wooden formwork for a building is costly and time-consuming. There is saying in the industry that concrete structures have to be built twice — once through the wooden formwork, then again in the concrete poured into the forms.

Using soil for the formwork could change that process. While it might seem like an unusual material compared to the solidity of wooden formwork, soil is firm enough to handle poured concrete. The EarthWorks method, as its known, introduces some additive materials, such as straw, and a wax-like coating for the soil material to prevent any water from draining out of the concrete. Using large-scale 3D printing, the researchers can take soil from a construction site and print it into a custom-designed formwork shape.

“What we’ve done is make a system where we are using what is largely straightforward, large-scale 3D printing technology, and making it highly functional for the material,” Curth says. “We found a way to make formwork that is infinitely recyclable. It’s just dirt.”

Beyond cost and ease of acquiring the materials, the method offers at least two other interrelated advantages. One is environmental: Concrete construction accounts for as much as 8 percent of global carbon emissions, and this approach supports substantial emissions reductions, both through the formwork material itself and the ease of shaping the resulting concrete to only use what is structurally required. Using a method called shape optimization, developed for reinforced concrete in previous research by Ismail and Mueller, it is possible to reduce the carbon emissions of concrete structural frames by more than 50 percent.  

“The EarthWorks technique brings these complex, optimized structures much closer to built reality by offering a low-cost, low-carbon fabrication technique for formwork that can be deployed anywhere in the world,” Mueller says.

“It’s an enabling technology to make reinforced concrete buildings much, much more materially efficient, which has a direct impact on global carbon emissions,” Curth adds.

More generally, the EarthWorks method allows architects and engineers to create customized concrete shapes more easily, due to the flexibility of the formwork material. It is easier to cast concrete in an unusual shape when molding it with soil, not wood.

“What’s cool here is we’re able to make shape-optimized building elements for the same amount of time and energy it would take to make rectilinear building elements,” Curth says.

Group project

As Curth notes, the projects developed by the Programmable Mud group are highly collaborative. He emphasizes the roles played by both Sass, a leader in using computation to help develop low-cost housing, and Mueller, whose work also deploys new computational methods to assess innovative structural ideas in architecture.

“Concrete is a wonderful material when it is used thoughtfully and efficiently, which is inherently connected to how it is shaped,” Mueller says. “However, the minimal forms that emerge from optimization are at odds with conventional construction logics. It is very exciting to advance a technique that subverts this supposed tradeoff, showing that performance-driven complexity can be achieved with low carbon emissions and low cost.”

While finishing his doctorate at MIT, Curth has also founded a firm, FORMA Systems, through which he hopes to take the EarthWorks method into the construction industry. Using this approach does mean builders would need to have a large 3D printer on-site. However, they would also save significantly on materials costs, he says.

Further in the future, Curth envisions a time when the method could be used not just for formworks, but to construct templates for, say, two-story residential building made entirely out of earth. Of course, some parts of the world, including the U.S., extensively use adobe architecture already, but the idea here would be to systematize the production of such homes and make them inexpensive in the process.

In either case, Curth says, as formwork for concrete or by itself, we now have new ways to apply soil to construction.

“People have built with earth for as long as we’ve had buildings, but given contemporary demands for urban concrete buildings, this approach basically decouples cost from complexity,” Curth says. “I guarantee you we can start to make higher-performance buildings for less money.”

The project  was supported by the Sidara Urban Research Seed Fund administered by MIT’s Leventhal Center for Advanced Urbanism.