The billions of tons of cement made each year have an enormous carbon footprint: 8% of global emissions, or four times more than the airline industry. That’s both because of the energy used to make cement—a process that involves heating up crushed rocks to as much as 2,800 degrees Fahrenheit—and because limestone, the main material, also releases CO2 directly when it’s heated. (Limestone is made mostly from calcium carbonate, and breaks down into lime, used in cement, and carbon dioxide.)
A growing number of startups are racing to make alternatives, including “biocement” made with microbes, concrete that can capture CO2 to help offset the emissions from making cement, and cement that replaces limestone with other rocks that don’t create the same emissions. A startup called Terra CO2 is in the latter group, and argues that it can scale up more quickly than its competitors because it uses accessible, cheap materials. The company announced today that it raised $46 million in a Series A round of funding led by Breakthrough Energy Ventures, the climate-focused VC firm launched by Bill Gates, and LENX, the investment arm of Lennar, one of the largest construction companies in the U.S.
The startup’s process partly replaces Portland cement, the limestone-based “glue” in concrete, with silicate rocks that are dug up in aggregate mines, which are already in operation all over the country. “Concrete is so massive, if you don’t have a scalable, raw material that you could pretty much get anywhere, you’re not gonna move the needle a lot,” says Bill Yearsley, Terra’s CO2, who spent 40 years in the construction materials industry before cofounding the startup. “And we are working with silicate rock types, which is the most abundant rock on the crust of the earth.”It plays the same role as fly ash, a waste product from coal manufacturing that is also used in concrete to partially replace cement. But as coal plants have closed, less fly ash is available—and, of course, burning coal isn’t compatible with climate goals. If Terra’s material is made with clean energy, it can have zero emissions. “We are technically able to produce a carbon neutral manufactured SCM today, however, our constraint is economics,” Yearsley says. Right now, the company can’t use renewable hydrogen or electricity and compete on costs, but it expects to eliminate emissions over the next five years.
Because the concrete companies also have mines producing the rocks that Terra needs, the startup will also be a customer, increasing the incentive for concrete companies to make the switch. “In most cases, we can use the lowest value of material coming out of their mines, the cheapest stuff, which makes their life easier,” says Yearsley. “And then we produce this [product] and we can sell that to them and they can turn around and use it in their own ready mix concrete plant.”
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