Concrete made from algae? Chicago firm offers a closer look at ‘bio-blocks,’ a zero-carbon alternative

As pedestrians head down Halsted Street in the Fulton Market district, a spiral structure in the middle of the Mews Pedway invites them to walk toward its center.

At a glance, the coil seems to have been assembled with traditional construction materials. But looks are deceiving — these building blocks were made of microalgae.

Dubbed “bio-blocks,” they offer a zero-carbon substitute to their concrete alternatives and were engineered by Prometheus Materials and the Chicago-based architecture firm Skidmore, Owings & Merrill, or SOM. They are being displayed as part of the fifth Chicago Architecture Biennial through the end of February.

“The installation itself that’s built there saves over a metric ton of carbon compared to an identical structure made with conventional concrete blocks,” said Ryan Culligan, design principal at SOM.

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

Engineers grow algae in photobioreactors, tanks surrounded by LEDs that mimic sunlight. Once the algae reaches a certain density, it is harvested and put in another tank, where it is stimulated until it mineralizes into calcium carbonate — the main component of shells and corals.

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

The calcium carbonate is then combined with natural binding agents to create a zero-carbon bio-cement, Burnett said. This cement gets mixed with sand and aggregate, much like the process to create concrete, and the mixture is then placed into a standard molding machine to create the blocks. After drying for a few days, the bio-block is ready to be used.

“Using bio-blocks in this installation was a no-brainer,” Culligan said. “In part because the amount of concrete blocks and cement that is used in the construction industry is so significant. Much of it is unseen and has an enormous carbon impact on the world.

At least 8% of global carbon dioxide emissions from human activities annually comes from cement and concrete manufacturing, accounting for over three times the CO2 emitted by the aviation industry. If the concrete industry was a country, it’d be the fourth-largest emitter in the world, according to Chris Magwood, manager on the carbon-free buildings team at the Rocky Mountain Institute, a Colorado nonprofit dedicated to research and consulting in sustainability and profitable energy innovations.

Many expect this footprint will only grow as the world keeps on building.

“From this month, today, until 2060, the amount of construction around the world that we should expect is as if a new New York City, completely built and completely formed, were to drop out of the sky onto Earth once per month for the next however many years,” Culligan said.

Since most of the emissions from concrete come from the making of one of its main components — cement — some approaches are focused on substituting other minerals for that cement.

But while these are good ideas that could work in reducing the amount of carbon released during the manufacturing process, Magwood said, there’s either not a large supply of those minerals or it’s expensive to get them.

“What’s super exciting about what Prometheus is doing is the way they’re making the cement part by growing algae,” he said. “That algae is actually taking CO2 out of the atmosphere. So if it all works, they’re actually creating a carbon sink in their cement, instead of emissions, which just changes the game.”

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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 really good if it is also carbon-negative, so from an evil material to a solution,” said Admir Masic, associate professor of civil and environmental engineering at the Massachusetts Institute of Technology.

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

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

Culligan pointed out that the use of bio-blocks is scalable because its production requires ubiquitous materials and common labor practices. According to SOM, the installation at 167 N. Green St. was assembled using conventional masonry techniques. Prometheus and SOM are hoping to license their technology to cement and concrete producers all over the world.

But this development faces its own set of challenges.

Magwood said concrete is already used at such a huge scale that its cost is really low, so there might be some resistance from the construction sector to switch to more sustainable materials.

“It’s been a commodity for 100 years, and it’s as low as the price can possibly be,” he said. “Anything new coming into the market is, by definition, going to be more expensive. So you’ve got that big hurdle to overcome.”

The new product would only really be able to supply the demand for blocks, which are a small fraction of the concrete used in construction since most of its volume is in ready-mix.

Prometheus — and the industry at large — still faces the issue of coming up with a zero-carbon alternative for ready-mix concrete, the quality of which will be harder to prove because of the variety of available mixes with distinct characteristics and purposes.

“We don’t know how these new materials will perform over 50 years,” Masic said. “We could guess through accelerated aging tests. But it’s very, very difficult to change the standards of industry.”

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

Masic said that while there are scalability challenges, possible solutions like the bio-blocks “push the imagination.” And those challenges are necessary to eventually achieve something that is inexpensive, durable and democratic.

“Prometheus is kind of the first to not just do a lab-scale experiment that shows it’s possible,” Magwood said, “but they’re in small-scale production now. And it’s exciting that they figured out that not only can we do this, but here’s how we would do it. That’s a pretty big, important step toward being able to address that huge pool of emissions.”

adperez@chicagotribune.com