How To Build A Climate-Friendly Skyscraper: Start Petri-Dish Small.

Prometheus Materials has a solution for replacing one of the biggest contributors of greenhouse gasses, financial backing from Microsoft and an aggressive plan to scale up quickly.

_By_{Amy Feldman}_{, Forbes Staff}

We love concrete. We use it everywhere — skyscrapers, data centers, roofs, sidewalks, homes. The problem is, concrete doesn’t love us. Its key ingredient, cement, is the source of 8% of the world’s emissions of carbon dioxide, a gas that’s catastrophically warming the planet. But how do we replace a material that’s so inexpensive, so durable and so popular?

Prometheus Materials has an intriguing answer. The University of Colorado spinout is turning algae into cement using a process that’s similar to how coral and seashells naturally form. “Climate change is potentially an existential problem, and we’re finding that nature may have provided us with the keys to a solution,” says Loren Burnett, the company’s cofounder and CEO.

Prometheus is still in the early stages of commercialization with minimal revenue from a test facility in Longmont, Colorado, near Boulder. But it’s figured out the science and is now raising what Burnett expects will be between $15 million and $35 million in venture funding (plus additional project financing) to build a 35,000-square-foot factory to make at least a half-dozen different varieties of precast, bio-concrete products, including blocks, panels and pavers.

Burnett expects that the combination of the factory’s production and a licensing strategy that will allow it to sell its bio-based material in powdered form to producers worldwide will help it reach $75 million in revenue by 2027. “The key here is that we’ll leverage the large producers of cement and concrete using their production and distribution facilities,” he says.

That’s a big number, but even if Prometheus reaches that goal it’s barely a drop in the bucket for the more than $300 billion global cement industry. That helps explain why Prometheus is one of a number of startups now trying to tackle the hard problem of cement.

Biomason, for example, has developed a similar way to grow cement bricks and tiles with bacteria. Terra CO2, with a different low-carbon alternative to cement, has raised money from Bill Gates’ Breakthrough Energy Ventures. Brimstone Energy is working to commercialize carbon-negative cement and is building a pilot plant near Reno, Nevada with backing from venture firm DCVC. All three have gained more venture funding than Prometheus, with Brimstone raising $60 million, Biomason $87 million and Terra CO2 $99 million, according to venture-capital database PitchBook.

Gates, who wrote a book called How to Avoid a Climate Disaster, has called out the desperate need to come up with a cleaner and affordable alternative to cement to fight climate change. Cement is a major producer of greenhouse gasses both because of the chemical reaction that creates it and the fossil fuels required to heat the kilns where it’s produced. “We don’t have a way of doing it that’s clean, that doesn’t cost dramatically more, more than twice the price,” he told NPR’s Marketplace in 2021. “So if people think it’s just passenger cars and electricity, they’re going to miss what we need to do to get to zero.”

To bring the cement industry in line with the Paris Agreement on climate change, its annual emissions would need to drop by at least 16% by 2030, even as cement production is slated to increase, according to a 2018 report by the London-based think tank Chatham House. “This problem is so huge it’s going to take all of us being wildly successful,” Burnett says of his company and its competitors. “Everywhere you look, you’re going to see concrete. It’s ubiquitous.”

Petri Dish Days

Four University of Colorado Boulder academics, Jeff Cameron, Sherri Cook, Mija Hubler and Wil Sruber — all Prometheus cofounders and advisors — stumbled onto the idea while searching for a solution to a different problem.

They’d received a $2.4 million grant from the Department of Defense’s research arm in 2017 to see if they could use biology to produce protective structures in deserts and other remote environments with difficult terrain. “They knew they couldn’t fly in concrete because it’s too heavy, and they knew they didn’t want to truck it in over large expanses of hostile territory,” Burnett says. “So if they could use local materials to produce hardened structures to protect troops and high-value military assets, that’s what they wanted to do.”

The researchers began testing bacteria in petri dishes to see what they could come up with. At first they worked with ureolytic bacteria, which had been studied for civil engineering applications, but they eventually switched to cyanobacteria, commonly known as blue-green algae, which gets its energy from photosynthesis. As they delved deeper, the Defense Department asked them to make a little two-by-two cube of the material. “We learned quickly that a lot of the challenges we had to address were in the scale-up,” Hubler says.

Today, the company grows its algae in narrow 1,350-liter tanks with artificial seawater that’s full of nutrients, bubbled air to provide carbon dioxide and LED lights to mimic sunlight. Prometheus harvests the algae and puts it in a separate tank and, using a proprietary process, stimulates what’s called biomineralization — the formation of minerals into biological structures. “That’s our secret sauce,” Burnett says. The result is a slurry that it dries into a powder and combines with proprietary natural binders to create a zero-carbon bio-cement. The material can be mixed with the granular material known as aggregate to form bio-based concrete. The final bio-concrete blocks look pretty much like those made with the industry standard, Portland cement.

Decarbonization Bug

Burnett, 66, a serial entrepreneur, previously founded five companies, four of which were based on tech transfer from a university or a lab. In 2011, he created the now-dormant e-Chromic Technologies based on technology licensed from the Department of Energy’s renewable energy lab for a window technology that reflected infrared radiation back into the atmosphere to reduce the need for air conditioners and cooling. “That’s where I got bitten by the decarbonization bug,” he says.

In February 2021, the University of Colorado’s tech-transfer office connected Burnett with the four professors, and the next month they founded the company together.

The early stages of a university spinout are tough because academic researchers can’t use their school labs for commercial work, but raising money takes more than just theoretical proof that the technology works. Cameron set up a basement lab in his house with fish tanks and bubbling apparatus purchased from pet stores. “We were sending samples to some of our investors that me and my kids actually made,” Cameron says.

A year later, the startup raised $8 million in venture funding led by European life sciences firm Sofinnova Partners that included strategic investors Microsoft, architectural firm Skidmore Owings & Merrill and roofing giant GAF. That enabled Prometheus to start pilot projects.

In a video, Microsoft president Brad Smith calls out the need for new innovations in concrete to bring down greenhouse gas emissions, singling out Prometheus and another company in which it’s invested, CarbonCure. “At Microsoft, we think about this a lot because a lot of concrete goes into our campuses and data centers,” he says in the video. Prometheus has since done a prototype project with Microsoft, which is building hundreds of data centers worldwide each year. “When we invest in emerging technologies, we look at if this is feasibly mainstream by 2030,” says Brandon Middaugh, senior director of the Microsoft Climate Innovation Fund, noting that the 2030 deadline of the Paris Agreement no longer seems so far away. “We see the potential is there, and there’s a pathway to scale for them.”

‘The Bleeding Edge’

Skidmore, Owings & Merrill, the global architectural firm known for skyscrapers that include the Burj Khalifa in Dubai, the tallest building in the world, and New York’s One World Trade Center, had also been looking for ways to reduce its carbon footprint with new materials. Four years ago, it began setting up partnerships with companies that could help, says Brant Coletta, managing partner and head of the firm’s global research and innovation team. In its partnership with Prometheus, it tested bio-materials to see if they could meet specs for things like strength and fire resistance. Working with masons, it built mockups and left them outdoors to see what might happen when exposed to the elements, then sprayed them with cleaners for additional testing. “We’re pushing them, and they’re pushing themselves, to get past all these tests so we can get to pouring concrete in skyscrapers,” Coletta says. “They’re at the bleeding edge of this.”

In February, Prometheus received industry certifications for both load-bearing and non-load-bearing blocks, an important step as it moves to commercialization. Skidmore, Owings & Merrill keeps pieces of the bio-concrete in its offices around the world for clients to see, and plans to exhibit a spiral-shaped sculpture at the Chicago Architecture Biennial this fall. While that may sound fancy, Coletta expects that the first major customer will be a data center.

There’s a lot that still has to happen to get Prometheus’ bio-cement into real projects, and the risks remain high. First it needs to raise the funds to build the factory, which it expects to get up and running in 2024, and then it needs to show it can successfully produce materials at a price customers will pay. It will also need to get its bio-cement past additional testing, and convince major concrete producers to take a chance. Burnett, who figures that the company will be producing at capacity and setting up licensing agreements by 2025, is determined.

“We have to decarbonize both cement and steel if we are going to be at net zero by 2050,” he says. “The math just doesn’t work without those two things happening.”