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Cement is responsible for 8% of global emissions, but there is a solution

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The 30 billion tonnes of concrete the world makes each year has a massive carbon footprint. Cement, the main ingredient, is responsible for around 8% of global emissions, meaning if it were a country it would be the third biggest climate polluter on the planet.

A California startup called Brimstone Energy has patented a new process that reduces emissions from Portland cement (the most commonly used type) to zero. Used with renewable energies, the process is actually carbon negative, meaning the cement could go from being a climate problem to being a solution.

Energy is part of the problem in traditional cement making because it runs on fossil fuels and involves heating a furnace to over 2,500 degrees Fahrenheit. But even though the cement factories have powered the whole process with renewable energy, it remains a fundamental challenge due to the chemistry. “You start with a rock called limestone, and limestone is basically solidified CO2,” says Cody Finke, co-founder and CEO of Brimstone, whose backers include Bill Gates’ Breakthrough Energy Ventures. When limestone, or calcium carbonate, is heated to high temperatures, it creates lime, an ingredient in cement. But a huge amount of CO2 is released at the same time.

[Photo: Brimstone Energy]

Sulfur instead uses another type of rock, calcium silicate, which does not produce CO2 when heated to produce lime. It creates silica, a by-product that can be used to replace fly ash, a waste from coal-fired power plants that is another typical cement ingredient. “This process was invented around peak coal, to match the energy system,” says Finke. With the demise of coal-fired power plants, the material is less available and is an additional source of emissions in the standard product (although carbon accounting typically does not include fly ash in its calculation of the total cement footprint. ).

[Photo: Brimstone Energy]

While a handful of other startups are working on making new types of cement that also reduce emissions, Brimstone wanted to make Portland cement, the industry standard, which has a specific chemical makeup. Finke says engineers aren’t inclined to take risks on new materials, for obvious reasons. “You can either build your building with the exact same material as every building on the planet, or you can build your building with a new material that no skyscraper has ever been built with before,” he says. Because the risk is so huge if something were to go wrong – potential deaths and hundreds of millions of dollars in costs for large buildings – engineers want to keep choosing something that has been proven to work.

“Entrepreneurs have struggled for decades to develop cement formulas that sequester more CO2, or provide equal strength with less mass, or blend cement ingredients in less polluting proportions,” says Zachary Bogue, co-founder and partner director of DCVC, which just invested in a seed funding round for Brimstone with Breakthrough Energy Ventures. “None of the alternatives worked very well: sequestration captured only a fraction of the CO2 and playing with the cement recipe worried regulators concerned about structural integrity. “

When Brimstone processes the calcium silicate, the startup will also end up with piles of magnesium, a rock that naturally absorbs CO2 from the air. This means, says Finke, that even if the cement is made with fossil fuels at the moment, it will still be carbon neutral. If it’s made from renewable energy, it “would be very carbon negative,” he says.

The company is currently designing its first pilot plant and will partner with existing cement and concrete manufacturers. When the product hits the market, it is expected to cost the same as traditional Portland cement, if not less. That’s the only way it could get adopted quickly, says Finke, noting, “My theory of change is that things never went from cheaper to more expensive. They always go from the most expensive to the cheapest.


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