Startup Minus Materials uses microalgae to make carbon-neutral cement

On a trip to Thailand for his honeymoon, while swimming above a coral reef, Wil Srubar thought of the beauty of nature, but he also thought of cement. In the reef, microalgae were growing calcium carbonate, a key material used to make cement, the glue that holds concrete together. Srubar, a materials scientist who teaches at the University of Colorado at Boulder, realized that this type of algae could help reduce the massive carbon footprint of the concrete industry.

Wil SrubarCEO of Minus Materials, holds a concrete cube sample containing biogenic limestone produced by the calcification of macro- and microalgae. [Photo: Glenn Asakawa/CU Boulder]

“I had worked a lot with alternative cements,” he says. “But it wasn’t really until I was snorkeling on my honeymoon that I started to really think about how these organisms, these macro and microscopic algae, develop these structures. Everything what they need is sunlight, seawater and CO2. Grown on a large scale in ponds, microalgae, called coccolithophores, could begin to provide the cement industry with another source of calcium carbonate.

Currently, cement production is responsible for approximately 8% of global emissions, more than double the emissions of the airline industry. Some of these emissions come from energy consumption. But the basic chemistry of the process is also an environmental problem, since the manufacture of cement consists of heating limestone (composed of calcium carbonate), which triggers a chemical reaction, releasing enormous quantities of CO2. If limestone could be made with algae and capture CO2 as it grows, Srubar knew part of the process could become carbon neutral.

A scanning electron micrograph of a single coccolithophore cell, Emiliania huxleyi. [Image: Alison R. Taylor/University of North Carolina Wilmington Microscopy Facility/Wiki Commons]

If this type of “biogenic” limestone is used along with other changes in cement production, including a shift to clean energy and carbon capture, cement manufacturing could actually be carbon negative, which which means it could capture more CO2 than it produces.

Several startups are working to reduce emissions in cement and concrete in different ways. Brimstone Energy replaces limestone with a different rock that does not emit CO2. Another company, Biomason, uses bacteria and other materials to form calcium carbonate. Others partially replace the cement with different materials or integrate the captured CO2 into the concrete.

Srubar, who extended his microalgae research to the startup Less materials, argues that using microalgae to make limestone has unique benefits. First, unlike some cement alternatives, the end product is Portland cement, the industry standard, which has a specific chemical composition. “We don’t have to change anything in the production of Portland cement,” he said. No new equipment is needed and the product already meets existing standards. It can reduce emissions by 60% or, if combined with other changes, by more than 100%. And it can compete on cost. “We have a path to cost parity with traditional limestone,” Srubar says.

Carbon negative concrete containing biogenic limestone from Minus Materials poured, placed and finished in a pilot demonstration in conjunction with Microsoft, the University of Colorado at Boulder and Boulder Ready-Mix Concrete. [Photo: Minus Materials]

Like other microorganisms, algae grow rapidly, doubling within hours. The startup estimates it can grow between 25 and 50 tons of limestone per acre per year. The cost has the potential to be low as the algae can also create other products; the algae itself can be transformed into food or cosmetic ingredients or biofuel. “They are very high in fatty acids, lipids, proteins and sugars which are precursors to some high value chemicals,” he says.

[Photo: Minus Materials]

Minus Materials, which received an undisclosed seed investment from the global venture capital firm SOSV, plans to launch more fundraisers this fall and hopes to begin pilot-scale production within 12 to 24 months. It is already starting to provide small samples to partners in the cement industry and companies, such as Microsoft, that are looking for new ways to decarbonize. Srubar envisions eventually forming a network of global production sites that can supply the biogenic limestone locally, around the world. “What we want to demonstrate with our large-scale pilot culture is that this is a replicable model anywhere in the world,” he says.

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