Builders of a better world … cement creates 8% of global carbon emissions … Brimstone’s carbon-negative cement is set to revolutionise the construction industry

May 14, 2023

Cement production is responsible for about 8% of global carbon dioxide emissions and 5.5% of total global greenhouse gas emissions.

Although several companies are exploring solutions, many only partially reduce emissions or end up with a product that can’t be used as a one-to-one replacement in existing processes. Brimstone, a startup that raised a $55 million funding in 2022, makes Portland cement, the most common type, and cuts emissions by replacing one ingredient—limestone—with silicate rock, which, unlike limestone, doesn’t produce CO2 when it’s heated as part of the cement-making process. The process also creates silica, a by-product that can be used to replace another ingredient in typical cement, called fly ash, which usually is sourced from coal-fired power plants.

In addition, the silicate processing also creates magnesium rock, which naturally absorbs CO2 from the air. This means that if Brimstone’s cement is made with renewable energy, the process is actually carbon negative, meaning it stores more carbon than it emits. It’s also lower cost than conventional cement. Brimstone has proven that its technique works and is using its recent funding to erect its first plant, which will be operational in 2024.

A new process to make ordinary cement

Brimstone was founded by two scientists who grew up halfway around the world from each other, bonded in Beijing where they traveled to talk toilets and are now aiming to solve that massive cement problem.

Co-founders Cody Finke and Hugo Leandri overlapped while doing graduate work at the California Institute of Technology in 2017, where they were both working on wastewater treatment. But the pair really bonded when they both attended the Reinvented Toilet Expo in Beijing in 2018.

In 2022 Bill Gates’ climate finance firm, Breakthrough Energy Ventures, and DCVC, a Silicon Valley venture capital firm, announced a $55 million funding round in Brimstone, saying “We need to recognise that cement is a massive problem for climate and that nobody has figured out how to address it at scale without dramatically increasing costs or moving away from the regulated materials that the construction industry knows and loves.”

A new process to make ordinary cement

Normally, creating cement involves heating up limestone, which releases carbon dioxide. Even if the energy used to heat up the limestone is 100% clean, 60% of the carbon emissions would remain because of what is inherently in the limestone rock, Finke said.

Some companies are working to make climate-friendly cement by capturing the carbon dioxide and storing it underground or using it. Other companies innovating in the space make an alternate product that serves the same functions as cement but is not cement.

Brimstone’s process creates what’s known as ordinary Portland cement (OPC), but instead of using limestone, it involves grinding up calcium silicate rock and using a leaching agent to pull out the calcium. Calcium silicate makes up about 50% of the Earth’s crust, according to Finke, and is so common that it’s often crushed up and used to make gravel. The process is subject to four patents.

Incidentally, the company’s name comes from an archaic term for sulfur, which was used in a previous version of its process. “We no longer use sulfur, but we still use stones, and we have a fiery passion for decarbonization,” says Finke.

Investors like the company’s focus on creating industry-standard cement at a similar or cheaper price point, instead of an alternative that might be more expensive and have to clear new regulatory hurdles.

“Brimstone is the first company we’ve seen that can make the same exact material that we use today to build our buildings and bridges — ordinary Portland cement – but without carbon emissions and with the potential to cost the same as, or less than, traditional cement,” says Roberts.

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