Climate technology companies say they have taken CO2 out of the air and trapped it in concrete for the first time

A trio of companies say they have taken carbon dioxide from the atmosphere and used it to make concrete for construction projects in California’s Bay Area.

According to the announcement Friday, this is the first time this has been done anywhere in the world. And if the effort gets off the ground, it could become a useful strategy to reduce the huge amount of greenhouse gas emissions that come from concrete.

Cleaning up the mess from concrete has become one of the toughest climate challenges and a magnet for Big Tech funding. Concrete is responsible for about three times as much carbon dioxide pollution as aviation. And it’s no wonder the stuff has a huge impact on climate change, since it’s the most consumed material on Earth next to water.

The announcement marks the success of a very small demonstration project, so it’s not something likely to have much of an impact yet. The hope is that eventually taking carbon dioxide out of the air and turning it into concrete will help slow climate change in two ways. First, it reduces the CO2 emissions humans have already emitted and traps the greenhouse gas where it can no longer warm the planet. The second goal is to make concrete in a way that doesn’t cause much more CO2 pollution.

California-based startup Heirloom was responsible for the first step in that process. The technology uses calcium oxide from limestone, which acts like a sponge to remove carbon dioxide from the ambient air. So far, Heirloom can only do this on a small scale with a demonstration plant in Brisbane, California. But it already counts Microsoft, Stripe, and Shopify as its customers — companies that were early excited about this future climate solution dubbed “direct air capture.” Bill Gates’ investment fund, Breakthrough Energy Ventures, has also funded Heirloom and its partner in this project, CarbonCure Technologies.

Founded in 2012, CarbonCure already uses CO2 residues from industrial processes to make concrete. Some of the concrete has even been used to build Amazon’s second headquarters in Arlington, Virginia. Most of the carbon dioxide the company uses comes from ethanol and ammonia production; this is the first time that CarbonCure has been able to use CO2 from the air. This has the added benefit of removing some of the pollution caused by human activities in the past. And once the carbon dioxide is trapped in the concrete, CarbonCure expects it to potentially stay there for thousands of years — even if a building it goes into is one day torn down.

The process can also reduce future emissions. For the Heirloom demonstration project, CarbonCure injected the CO2 into wastewater so that it could be reused to make new concrete. Normally, the waste water would be thrown away as it is too reactive to be reused. But that wastewater contains some cement residue – the main ingredient in concrete. Cement is particularly polluting because it is usually heated at very high temperatures, which consumes a lot of energy. In addition, a chemical reaction in the cement production process causes extra CO2 emissions.

So the key to making concrete in a way that is less damaging to the climate is to use less cement in the mix. Injecting CO2 into the wastewater makes it less reactive and saves the remaining cement in it. If you then reuse that water, you also reuse that cement. That way you don’t have to invest that much fresh cement in the concrete mix. That is exactly what the third company in this demonstration project, Central Concrete Supply Company, did. It used the treated wastewater to make concrete at its plant in San Jose, California.

However, it is probably still too early to declare a climate victory with this project. It was a very small test drive that used just under 38 kilograms of captured CO2, roughly equivalent to the emissions of driving a car for about 150 kilometers. And there are still no exact measurements of how much additional emissions could have been avoided by reusing the wastewater treated with CO2.

“There should be more analysis [to better assess the sustainability claims] – and for that we need data that is publicly available,” said Dwarak Ravikumar, assistant professor of civil and environmental engineering at the University of Waterloo. That is important to ensure that there are no steps in the process that negate some of the potential climate benefits. For example, capturing carbon dioxide can be energy intensive, even though Heirloom says its technology runs on renewable energy.

The companies say they hope for economies of scale. And new climate policies have boosted these kinds of technologies with tax credits and federal funding. The Inflation Reduction Act is pumping billions of federal dollars into developing direct air shelters. And all that captured carbon has to be stored somewhere. Underground wells are an option, but that route can take a lengthy permitting process.

“Concrete is ready today,” said Shashank Samala, CEO of Heirloom. “It’s everywhere. It’s the world’s most abundant resource and it’s a fundamental blockage to our lives.”