Using Concrete in a Smarter, More Sustainable Way

This is the question Associate Professor Pablo Moyano Fernández is testing with his project Avis Spiralis, a bird blind at the Audubon Center at Riverlands that opens to the public this fall. His new method of casting concrete, called Opus Versatilium, argues that concrete can be affordable, accessible, durable, sustainable, and beautiful.

Concrete has long been a research interest for Moyano Fernández, who grew up watching his older brothers work in construction and engineering. “Concrete is the number one construction material used across the world, by far. We use concrete for foundations, infrastructure, roads, buildings, structures, envelopes, and so on,” he says. “Today, it’s unrealistic to use less concrete or replace it with another material. So the question is, can we use it in a smarter way, in a more sustainable way?”

Typically, concrete building envelopes are cast in full-height forms which are over-dimensioned to withstand the pressure of wet concrete. “In any concrete job, the formwork can be 30-70% of the cost,” Moyano Fernández says. The forms are sometimes single-use and are immediately sent to the landfill after use. And, any customization in geometry or texture of concrete forms is limited and comes at a cost.

Knowing that formwork was such a limiting factor, Moyano Fernández started exploring alternative methods to shape concrete. He 3D-printed six-inch molds, a drastic reduction from the full floor-to-floor height plywood forms typically used in construction. “You can clamp these plastic molds with cheap clamps from the hardware store, cast a row, and while it’s curing, move molds from an earlier section and start casting the next,” Moyano Fernández says. This section-by-section approach significantly minimizes the pressure of the concrete and allows the molds to be used over and over again. “If you have a 3D printer, simple tools, and concrete,” Moyano Fernández says, “I’m arguing that, in some places, you could build a whole house with minimal guidance, minimal planning, and minimal investment.”

The trade-off for the method’s affordability and customization is that it can take longer to build than a traditional concrete building envelope. But at the same time, it’s possible to build with a very small crew and completely off-grid — Moyano Fernández built Avis Spiralis almost entirely on his own, with some help from his students during site visits, along with help from one assistant — his son. “My teenage son, Benicio, wanted to get stronger, so he helped me during school breaks,” he smiles.

The bird blind’s design includes an element of beauty — shapes of native birds placed throughout the spiral. The silhouettes were inspired by the halftone printing technique and made possible by the ability to easily make custom molds. “Because the molds are small, you can create different patterns, textures, and shapes” Moyano Fernadez says. “You can do very, very complex geometries with really minimal formwork.”

Moyano Fernández sees concrete as a durable, sustainable material. “Concrete can withstand not just flooding, but also fire, strong winds, tornadoes, hurricanes, and high temperatures,” he says. He added that concrete requires very little maintenance, has high thermal mass, and is soundproof — all good things for sustainable buildings that require less energy to operate. Moyano Fernández points out that the Pantheon in Rome is made of concrete, and is still standing more than 2,000 years later.

Today, concrete has to overcome its reputation as a material that requires too much production energy to be considered sustainable. “The cement in concrete takes a lot of energy to produce. Heating the limestone to form cement releases a lot of carbon dioxide — but, cement is only 8-15% of concrete,” Moyano Fernández says. “When you compare concrete to brick, glass, aluminum, steel, even plywood, concrete is actually much, much lower in terms of embodied energy.” And, he says that researchers and the construction industry are investigating how to diminish the carbon footprint, from optimizing production methods to changing the composition of concrete, in some cases replacing some of the cement with byproducts from other industries.

In Avis Spiralis, Moyano Fernández estimates he sourced 85% of the components locally. The sand and gravel come from a quarry just four miles away. “The only thing that is not local is the cement, which is applicable to most building sites around the world,” he says. His hope is that the wide availability of ingredients means the system can be implemented in almost any context.

Moyano Fernández made a proposal to the Audubon Center at Riverlands to build the bird blind and secured funding for materials from WashU, the Audobon Center at Riverlands, and industrial partners, notably Ram Jack St. Louis. “This was the perfect opportunity for me to put into practice all of this theory that I’ve been researching and really test it as a proof-of-concept, applying this system to a real structure,” he says.

During construction, Moyano Fernández brought his students on a field trip to see the concrete casting process in action. “I try to integrate my teaching and research as much as I can, and always with a very hands-on approach,” Moyano Fernández says. He regularly teaches a studio on concrete, where students have a lot of freedom to dream up new designs. “They really push the envelope and challenge industry standards or the system I’m proposing — I see it as mutual feedback.” he says.

The site is just a few steps away from the Mississippi River and sees hundreds of species of birds each year, both native and migratory. Visitors can climb the interior ramp of Avis Spiralis for 360-degree views of the area, watching Bald Eagles, Trumpeter Swans, Great Blue Herons, and more.

“My hope is that people can enjoy this project for literally hundreds of years,” Moyano Fernández says. “I’m convinced that the concrete I’m using can withstand centuries without any kind of deterioration and requiring no maintenance. But most importantly, it’s for the people who go to the site to enjoy nature, watch birds, and learn about local ecologies.”

“If the system proves to work, that will be an encouragement to further my research and apply this to other projects and produce affordable, highly customized building enclosures,” he says.

Moyano Fernández documents his process in an upcoming book, “Concrete Load-Bearing Walls: Digital and Material Technologies for Sustainable Building Envelopes.” His article, “Opus Versatilium: A Meta Vernacular Approach for Contemporary Load-Bearing Walls,” was published in the Plan Journal in 2024.