Over the next 10 minutes, construction workers around the world will pour around 76,000 metric tons of concrete—three times the weight of the Statue of Liberty—for roads, buildings, bridges, and other infrastructure. In a year, the building industry will produce more than 4 billion metric tons of the material. It’s so ubiquitous that it tends to go unnoticed, but it’s also one of the world’s biggest sources of CO2 emissions.
Producing cement, the glue that holds concrete together, uses high temperatures that require huge amounts of energy. And limestone, a key ingredient in cement, emits CO2 as it’s processed. The industry pumps out around 4 billion metric tons of emissions a year, roughly four times as much as the airline industry. But new technology from a company called Solidia shrinks the carbon footprint of production. By injecting captured CO2 into the process, it can eventually make concrete carbon negative.
“We’re sinking a significant quantity of carbon into the end concrete product,” says William Tynan, CEO of Solidia, the company making the technology and the winner of the spaces, places, and cities category of Fast Company’s 2021 World Changing Ideas Awards. The company, which uses a chemical process licensed from Rutgers University, reduces emissions in a few different ways. Its recipe uses less limestone. It also requires less heat, so it’s possible to save energy. And instead of using water to cure the concrete, the process has been tweaked to use CO2.
The company is now working with commercial customers to use the process to make concrete pavers and blocks. The new material is stronger and brighter than typical concrete, and cures faster, around 24 hours instead of nearly a month.
“It’s critical that it has these other advantages,” Tynan says. “There’s an increasing demand for greener products. But ultimately, this is a large commodity industry where there has to be economic value created in order for adoption to occur. . . . This is an industry that hasn’t changed in hundreds of years, and has been around for thousands of years. People know how to do things a certain way. And so a lot of our work is helping bring them along and proving to them that they can make more money.” (Concrete manufacturers have some up-front costs to set up the new system, but the speed of production can reduce costs over time, and they can choose to charge a premium because of the aesthetics and sustainability of the product. Cement manufacturers can also save money on energy and production time, and if carbon pricing is later introduced, will save money because of the lower carbon footprint.)
The current process reduces emissions by nearly a third. Shifting parts of the process to be powered by renewable energy, something that could also soon be feasible, could reduce emissions more. But the company is also working on a new process that goes even farther. Using CO2 in a liquid form rather than a gas makes it possible to put four times as much CO2 in the final product, making it carbon negative. “That is more than enough to potentially cover all of the emissions of the production of the cement and the production of the concrete,” he says. The company is tweaking the process now, but says it will be achievable.
Other startups are also working on the problem, such as CarbonCure, which also embeds CO2 in concrete, or CarbiCrete, which uses a waste product from the steel industry in place of cement. The world needs alternatives now because of the scale of the industry and the fact that it’s growing even larger, Tynan says. “These are products that aren’t going away. We’re not going to be using less concrete and less cement as the populations continue to grow and cities continue to expand. We’re talking about multiple gigatons of CO2 emissions that can be addressed if technologies like Solidia’s are adopted in the industry.”