This startup wants to decarbonize concrete production by using CO2 as an input

By some measures, the world really is a concrete jungle.

Concrete is the most abundant man-made material on earth—water is the only resource humans consume more of—because it’s durable, versatile, and relatively cheap. It’s also the single largest industrial emitter of carbon dioxide.

Producing the main ingredient in concrete, cement, accounts for ~8% of global CO2 emissions each year.

Demand for concrete has tripled over the last 40 years and experts expect it will only continue to rise in the coming decades. That means production of concrete will likely increase even as the cement sector needs to cut its emissions by at least 16% by 2030 to be on track for Paris Agreement goals.

Shrinking the carbon footprint of concrete requires either using less cement or reducing the carbon impact of cement production, Christie Gamble, senior director of sustainability at CarbonCure Technologies, told Emerging Tech Brew.

CarbonCure is one company that aims to lower the carbon intensity of concrete by engineering a scalable way to use CO2 as an ingredient in concrete itself. The Canadian startup has raised $12.4 million since it was founded in 2007, with investments from Amazon and Breakthrough Energy Ventures.

From flour to bread

While concrete and cement are sometimes used interchangeably in less technical conversations, they are two different products.

“Cement is kind of like the flour, whereas concrete is the bread,” Gamble said.

Of course, making cement is a bit more complex than making flour—and it definitely requires a lot more energy. The typical process starts with limestone, which is primarily made of calcium carbonate (CaCO3). Heating the limestone at extremely high temperatures separates the calcium oxide (CaO) from CO2.

This step, called calcination, is where cement’s high carbon intensity comes from: the energy needed to generate the heat, plus the CO2 waste byproduct, results in significant emissions.

Cement is then mixed with water and aggregates like sand and gravel to make concrete.

What to do about the CO2?

Efforts to develop lower-carbon alternatives to this cement production process by using different raw materials have run into challenges because of higher costs, supply shortages, and resistance from customers.

More efficient kilns can help with incremental improvements in the carbon intensity of cement production and technologies that use electricity rather than heat to split apart limestone are in early development stages, but most plans for cutting emissions in the industry rely heavily on carbon capture.

CarbonCure’s tech doesn’t capture CO2 from the cement production, but instead recycles CO2 captured by nearby industrial emitters such as ethanol and fertilizer plants, Gamble said. Its contribution is technology that injects CO2 directly into concrete, sequestering those emissions.

“We are working with cement and concrete providers all across the globe to reconsider CO2 as a beneficial ingredient in concrete itself in order to reduce its carbon footprint,” Gamble said.

Adding CO2 into the mix of cement, water, sand, and other materials that make concrete creates a chemical reaction that is essentially reverse calcination—the CO2 becomes a mineral, meaning it won’t be released back into the atmosphere even if the concrete is demolished.

CarbonCure sells carbon removal credits based on this permanent CO2 storage, which help the company further develop and scale its tech, but Gamble said the mineralization also makes this solution more cost-competitive with typical concrete.

“The mineral itself will improve the concrete strength. So if you did nothing else but just add CO2, you would get stronger concrete,” Gamble said. “What that allows for is for concrete producers to use less cement.”

Less cement means fewer CO2 emissions and lower costs for concrete producers.

Right now, the company’s technology is used by more than 500 concrete plants around the world, Gamble said. Projects including Amazon’s HQ2 and General Motor’s Tennessee EV plant are being built with CarbonCure concrete products.

Zoom out: CarbonCure has a goal of removing 500 million tonnes of CO2 annually from the concrete industry by 2030—in the last year, the technology has avoided more than 75,000 tonnes of CO2, according to the company—but it’s just one of many solutions that will be needed. For context, global cement production currently accounts for about 2.7 billion tonnes of CO2 emissions each year.

Government policies, such as the Low-Embodied Carbon Concrete Leadership Act signed into law in New York at the end of last year, can help by setting emissions standards for concrete used in public projects.

But there are many stakeholders involved in construction who can work to change the status quo, Gamble said.

“We need architects, engineers, building owners, [and] contractors to be asking for low-carbon concrete as part of their design. They need to include it in the design decisions,” she said.