Cement Is A Climate Nightmare. Here’s How One Boston Startup Is Eliminating Emissions
Source: Fast Company, Adele Peters
Photo: Getty Images
Sublime’s carbon-free cement was poured for a Boston building—the first time the product was commercially used.
Cement is a climate nightmare. Here’s how one Boston startup is eliminating emissions
Last month, on a bitterly cold day, a truck pulled up to a construction site in Boston and poured concrete. It looked and performed like ordinary concrete—but it was the first commercial use of a new cement designed to solve the industry’s climate problem.
Sublime, the MIT spinoff that designed the technology to make the new cement, could be the first company to fully decarbonize the manufacturing process. Right now, most cement is made in massive kilns heated with fossil fuels. The traditional process heats up limestone, which releases even more CO2 as it breaks down. The massive cement industry—which produces around 4 billion metric tons of the material each year—is responsible for around 8% of global emissions.
“I like to call Sublime the electric vehicle of cement making,” says Leah Ellis, cofounder and CEO at the startup. “We’re replacing the high-temperature combustion and fossil fuel process with an ambient temperature, electrochemical process that avoids the CO2 emissions entirely.”
Instead of using heat to break down rocks for cement, the startup uses chemistry to dissolve them, and then blends the components back together into what it calls “Sublime Cement.” The process can replace limestone with other minerals, including rocks found at high volumes in industrial waste, so it’s also possible to eliminate the emissions from limestone.
The technology moved quickly from the lab to reality. As a PhD student in Canada, Ellis had researched battery technology for companies like Tesla. As a postdoc, she came to MIT and started working with Yet-Ming Chiang, a professor who has helped launch a series of climate tech startups, and saw an opportunity to rethink how cement was made. After early experiments, Chiang and Ellis cofounded Sublime. Over the past four years, Ellis says, they’ve gone from producing a single gram of cement as a proof of concept to a pilot plant making 250 tons per year. The next plant, in development at the site of a former paper factory in Holyoke, Massachusetts, aims to open in 2026 and will have a capacity of 30,000 tons a year.
The new cement was designed to perform like ordinary Portland cement, and meets an international standard for that performance; when it’s mixed with water, the resulting concrete flows at the same rate as ordinary concrete, hardens in the same way, and is as strong and durable. When it’s finished with a trowel, the team worked to make sure that it had the same stickiness as concrete made with Portland cement, so a contractor working with it wouldn’t notice the difference.
Several other startups are working on different approaches to cutting emissions in cement production, including Brimstone, which makes a version of Portland cement that also avoids using limestone. When it runs on renewable energy, Brimstone’s process is also zero emissions; it creates magnesium as a byproduct, which can absorb extra CO2 from the air. But it, along with Sublime and others in the space, still faces the challenge of scaling up.
“It’s a race to scale,” says Ellis. Cement companies “don’t believe in Powerpoints,” she says. “They don’t want to see your models. They want to use your cement, they want to see your plant operating. It’s a very tangible industry.”
Sublime’s work on the Boston building, which used the new cement in a non-structural part of the ground floor, was an important step in validating that its tech worked as expected, Ellis says, from how it mixed in the concrete truck to how it was poured.
When it’s made a large scale, the cement should be able to compete in cost with traditionally-made cement. That’s in contrast to some other ways that cement companies are working to cut emissions, like carbon capture equipment that can double capital expenses.
By 2028, the startup aims to have a full-size commercial plant that can produce a million tons of cement a year. Of course, that’s still a tiny fraction of the industry’s production, and demand for concrete is growing quickly along with global construction. But Ellis believes that it’s possible to decarbonize the industry—not just rely on offsets—by the middle of the century.