With sustainable cement, startup aims to eliminate gigatons of CO₂

While today’s cement is made through extremely high temperatures in a kiln, ancient Romans didn’t have that option. Still, anyone who’s been to Rome recently will tell you that ancient cement seems to have held up just fine.

The startup Sublime Systems thinks the Romans were onto something. The MIT spinout has created a drop-in replacement for today’s most commonly used cement, known as portland cement, that uses electrochemistry to skip the ultrahigh temperatures of conventional production — and the immense carbon dioxide emissions that go with it.

“Romans couldn’t go to those obscene temperatures, but they’ve proven their cement is hard and durable, and we now have 2,000 years of innovation to get that cement to meet the criteria we expect out of modern cement,” explains Sublime co-founder and CEO Leah Ellis, who developed the approach as a postdoc in the lab of Sublime co-founder and MIT Professor Yet-Ming Chiang.

Sublime’s approach has potential to make a major dent in global greenhouse gas emissions. The International Energy Agency estimates that cement is responsible for about 7 percent of human-driven carbon dioxide emissions worldwide. Sublime’s process eliminates emissions by foregoing the high temperatures and the use of limestone, which is nearly 50 percent CO₂ by weight, in favor of a novel electrochemical process.

“Cement enabled civilization as we know it today, but now it needs to be reinvented,” says Chiang, who is MIT’s Kyocera Professor of Ceramics. “Cement creates about 4 gigatons of emissions a year, and by 2050 that’s projected to become 6 gigatons a year. I think of what we’re doing as technically a very feasible way of decreasing those 4 gigatons of cement emissions as soon as possible.”

In May, Sublime reached a major milestone when 3 tons of its cement was poured in Boston’s largest net-zero commercial building in the Seaport district. Now the company is building a commercial-scale manufacturing plant in Holyoke, Massachusetts, that will be able to produce 30,000 tons of cement per year. The new plant is slated to come online as early as 2026.

“The Holyoke plant is designed to be a module that we can repeat to get to a million-ton-per-year plant,” Ellis says. “That will allow us to eliminate scale up risk so we can deploy simultaneously all over the world.”

From batteries to cement

Ellis came to MIT in 2018 as a postdoc after receiving a fellowship from the Canadian government to study anywhere she wanted.

“I chose to work with Yet-Ming Chiang in part because he has a great track record of being really creative and useful with the work he does in science,” Ellis says. “That’s the type of work I wanted: to discover things and push limits and solve problems.”

Although they were both experts in batteries, Ellis embraced Chiang’s suggestion of working on something different, and Chiang suggested exploring ways of using electrochemistry to make cement production more sustainable.

“Cement is the largest CO₂ emitter in the industrial materials world, and concrete is the world’s most abundant material by volume, next to water, but it hadn’t gotten a lot of attention on how its production could be electrified,” Chiang says.

Ellis and a graduate student, Andres Blades, began reviewing the literature on cement chemistry and production, looking for a more sustainable manufacturing process that might benefit from the rise of cheap, renewable electricity. Her research moved from exploring fundamental chemistry and technological approaches to economic and industry analyses.

“My motto is just to try as hard as I can for as long as they’ll let me,” Ellis says. “I strove to make myself indispensable. We started talking to customers and really understanding the industry and what they needed to see from low-carbon cement, what their concerns were, what the regulatory landscape was like, and it just has evolved from there. I really haven’t stopped since.”

Once the founders decided their approach had potential, they published the research in Proceedings of the National Academy of Sciences and launched their company in March of 2020. Working through Covid-19 disruptions, the team licensed their patent filings from MIT’s Technology Licensing Office and participated in the MIT i-Corps program, which helps scientific founders talk to potential customers.

“MIT has so many resources,” Ellis says. “It's a real intellectual playground, and that makes it easy to start something up. There’s no textbook way to start up a company; it’s a game of constant exploration, and there's so much available to explore at MIT.”

At the core of portland cement’s huge carbon footprint is the use of limestone, which is nearly 50 percent CO₂ by weight. Nearly all that CO₂ is released when limestone is heated to high temperatures to create lime. The heating process also creates enormous amounts of CO₂ on its own, as it requires temperatures of 1,450 C, a temperature that is difficult to electrify efficiently.

At MIT, Sublime’s team created an electrochemical process in which it breaks down calcium silicate rocks at ambient temperature using electrochemistry. The reaction works with abundant raw materials and creates reactive calcium and silicates that are dried and blended into Sublime’s cement.

The mixture has the same final strength and hardened phases as portland cement and meets a standard performance specification in the industry that allows it to be used in building construction.

“To our knowledge, we are the only true-zero solution for manufacturing a drop-in replacement for portland cement, because we don’t use fossil fuels and we don’t use limestone, so we can avoid all of the emissions from making portland cement,” Ellis says.

Changing the way we build

At an event hosted by MIT Technology Review a few years ago, WS Development senior vice president Yanni Tsipis ’01 SM ’02 heard about Sublime’s process and reached out to learn more. The conversation led to Sublime’s first commercial pour earlier this year in the biggest net-zero office building in Boston.

“We hope our partnership with Sublime illustrates the power of the possible when new technology flows from incubator to industry,” Tsipis says. “The location in the building’s primary public space will be experienced by thousands of people every day and is an ideal way to share our aspiration and Sublime’s extraordinary technology with the entire innovation ecosystem in Boston’s Seaport and beyond.”

Sublime is one of several companies Chiang has founded since he joined MIT as a professor nearly 40 years ago. Chiang, who also serves on the climate search advisory committee as part of MIT President Sally Kornbluth’s Climate Project at MIT, believes Sublime’s journey exemplifies the power of MIT’s community to advance impactful new technologies.

“Sublime came from recognizing a problem where there’s clearly an unmet need, and getting on it early when others hadn’t yet recognized its importance, then moving quickly to a solution that you can scale with speed to mitigate climate change,” Chiang says. “This is all just very MIT to me. We really want to focus on doing things that matter — not just to other academics, but to society and to the world.”