Concrete made from algae? A Chicago company offers a closer look at “bioblocks,” a carbon-free alternative

By | December 22, 2023

As pedestrians walk along Halsted Street in the Fulton Market district, a spiral structure in the middle of the Mews Pedway invites them to walk downtown.

At a glance, the coil appears to be composed of traditional building materials. But appearances are deceiving: these building blocks are made of microalgae.

Called ‘bioblocks’, they offer a carbon-free replacement for their concrete alternatives. They were designed by Prometheus Materials and Chicago-based architectural firm Skidmore, Owings & Merrill, or SOM. They are on display until the end of February as part of the fifth Chicago Architecture Biennial.

“The plant itself built there saves more than a ton of carbon compared to an identical structure made with conventional concrete blocks,” said Ryan Culligan, design director at SOM.

The shell-like shape of the structure is a nod to the production techniques of the bioblocks themselves, which imitate a natural process called mineralization that creates shells and coral reefs.

Engineers grow algae in photobioreactors, tanks surrounded by LEDs that mimic sunlight. Once the algae have reached a certain density, they are harvested and placed in another tank, where they are stimulated until they mineralize into calcium carbonate, the main component of shells and corals.

“Unlike nature, it can take days, weeks, months or even years to create a coral reef. For example, we can do it in a few hours,” said Loren Burnett, CEO and president of Prometheus Materials. “So we bio-mineralize in commercially viable quantities and on time scales.”

The calcium carbonate is then combined with natural binders to create a carbon-free biocement, Burnett said. This cement is mixed with sand and aggregate, just like when making concrete, and the mixture is then placed in a standard molding machine to make the blocks. After drying for a few days, the bioblock is ready for use.

“Using bioblocks in this installation was a no-brainer,” said Culligan. “Partly because the amount of concrete blocks and cement used in the construction sector is so large. Much of it is invisible and has a huge carbon impact on the world.

At least 8% of global CO2 emissions from human activities annually come from cement and concrete production, which is more than three times the CO2 emissions from the aviation industry. If the concrete industry were a country, it would be the fourth largest emitter in the world, according to Chris Magwood, manager of the carbon-free buildings team at the Rocky Mountain Institute, a Colorado nonprofit dedicated to research and consulting on field of sustainability. and profitable energy innovations.

Many expect this footprint to only grow as the world continues to build.

“From this month, today, until 2060, the amount of construction we can expect around the world is as if a new New York City, fully built and fully formed, were to fall from the sky to Earth once a month for the next , however many years,” Culligan said.

Because most of concrete’s emissions come from the production of one of its key components – cement – ​​some approaches focus on replacing that cement with other minerals.

But while these are good ideas that could help reduce the amount of carbon released during the manufacturing process, Magwood said, there is either not a large supply of those minerals or they are expensive to obtain.

“What’s super exciting about what Prometheus is doing is the way they’re making the cement part by growing algae,” he said. “Those algae actually remove CO2 from the atmosphere. So if it all works, they are actually creating a carbon sink in their cement, rather than emissions, which just changes the situation.”

Carbon sinks absorb and store more carbon dioxide than they release; For example, forests are considered sinks because they remove CO2 from the atmosphere through photosynthesis.

“It would be very good if it was also carbon negative, so from a malicious material to a solution,” says Admir Masic, associate professor of civil and environmental engineering at the Massachusetts Institute of Technology.

Similarly, a researcher at MIT’s Concrete Sustainability Hub, Masic, called the material “democratic” for its reliability and durability, as well as its accessibility and cost-effectiveness.

“Let’s say democratic in the sense that wherever you go in the world you will find someone who knows how to mix concrete and make a house and a building,” he said.

Culligan pointed out that the use of bioblocks is scalable because their production requires ubiquitous materials and common labor practices. According to SOM, the installation at 167 N. Green St. was installed using conventional masonry techniques. Prometheus and SOM hope to license their technology to cement and concrete manufacturers around the world.

But this development has its own challenges.

Magwood said concrete is already in such widespread use that its cost is very low, so there could be some resistance from the construction industry to switching to more sustainable materials.

“It’s been a commodity for a hundred years and the price is as low as it can possibly be,” he said. “Everything new on the market will by definition be more expensive. So you have to overcome a big hurdle.”

The new product could actually only meet the demand for blocks, which make up a small part of the concrete used in construction, as most of the volume is ready-mixed concrete.

Prometheus – and the industry in general – is still faced with the issue of coming up with a carbon-free alternative to ready-mixed concrete, the quality of which will be more difficult to prove due to the variety of mixes available with different characteristics and purposes.

“We don’t know how these new materials will perform in fifty years,” says Masic. “We were able to guess it through accelerated aging tests. But it is very difficult to change the norms of the industry.”

Burnett said his company is hopeful that by the end of next year it will have developed other bioproducts, “all the way up to the ready-to-use mix.” Prometheus Materials, he said, is in the process of raising funds to build a facility where it can begin development and manufacturing on a commercially viable scale.

Masic said that while there are scalability challenges, possible solutions such as the bioblocks “capture the imagination.” And those challenges are necessary to ultimately achieve something that is cheap, sustainable and democratic.

“Prometheus is pretty much the first to not only do a lab-scale experiment that shows it’s possible,” Magwood said, “but they’re now being produced on a small scale. And it’s exciting that they figured out not only can we do this, but how we would do it. That’s a pretty big, important step toward addressing that enormous amount of emissions.”

adperez@chicagotribune.com

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