Sublime Systems’ low-carbon cement goes commercial

The startup’s cement is made using electricity instead of fossil fuels. Now the company is working to get contractors and construction crews to use it.
By Jeff St. John

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Workers smooth out concrete made from startup Sublime Systems' low-carbon cement at a construction site in Boston
Sublime Systems CEO Leah Ellis looks on as construction workers apply concrete made from Sublime’s electrolytically produced cement at the One Boston Wharf Road construction site in Boston. (David Degner / In Short Media)

In early May, Leah Ellis, CEO of startup Sublime Systems, stood watch as crews poured and raked concrete at a construction site in Boston. Her company’s fossil-fuel-free cement had been used to make that concrete, and the moment marked an important milestone.

That’s because the three tons of cement in the concrete being formed into the floor of the indoor public space of One Boston Wharf Road, the city’s largest net-zero commercial office park project, was the first commercial application of Sublime’s product.

Trying to get the construction industry, which is known for being resistant to change, to embrace a novel form of cement is no small thing.

Building owners don’t buy cement — they buy buildings,” Ellis told Canary Media. Developers don’t buy cement — they buy concrete. And they buy it from the concrete subcontractor, who buys it from the ready-mix supplier. And there are a lot of providers in the value chain there that don’t get credit for using low-carbon cement.”

What those companies do get credit for is providing high-quality cement and concrete at reasonable cost, she said.

Sublime’s cement is made by electrically charging a bath of chemicals and calcium silicate rocks at its pilot plant in Somerville, Massachusetts. Last September, a key standards body determined that it met the same specifications as ordinary Portland cement, a material that’s produced by the hundreds of millions of tons each year in fossil-fueled kilns at temperatures as hot as molten lava.

Now Sublime is concentrating on getting the customers it needs to justify the next phase of its growth. In March, the MIT spinout won an $87 million grant from the U.S. Department of Energy to build its first commercial-scale plant in Holyoke, Massachusetts, capable of producing tens of thousands of tons of cement per year.

To finance the remainder of the Holyoke project, it is critical for us to have advance market commitments,” Ellis said, to prove there are people who want to use this material and will pay for it.”

That’s why Yanni is so important,” she said, referring to Yanni Tsipis, the senior vice president at WS Development, the company developing the One Boston Wharf project. Tsipis, an MIT graduate and lecturer at the MIT Center for Real Estate, contacted Sublime after reading about the company in the MIT Technology Review.

This partnership with Sublime is to demonstrate the power of the possible when innovation flows from incubation into industry,” Tsipis told Canary Media. The location of this particular [concrete] pour will be experienced by thousands of people every day, and it’s a good way to share our aspirations.”

The plan for One Boston Wharf Road is to build and operate a 700,000-square-foot mixed-use office building with a greenhouse gas emissions impact that’s 90 percent below code requirements. To hit that target, WS Development is installing heat pumps designed to replace fossil-gas-fired boilers for heating large buildings, using the latest low-global-warming-potential refrigerants for its chillers, and contracting for renewable electricity to power the complex, he said.

While those choices reduce carbon emissions associated with building operations, low-carbon cement helps reduce the embodied carbon” footprint of buildings. Cement production is responsible for roughly 8 percent of global carbon dioxide emissions.

Today, the primary way of reducing the carbon footprint of the concrete that’s made from cement is to blend in lower-carbon substitutes — supplementary cementing materials in industry jargon. But to tackle the emissions of cement making itself, the world’s largest producers have set their greatest hopes on carbon capture — an expensive and complex industrial-scale solution with unclear prospects over the next few decades.

We’ve seen a number of what I’ll call carbon-capture products pitching themselves as low-carbon concrete,” Tsipis told Canary Media. All of these products, without casting aspersions on them — they’re doing great things for the planet — but they still rely on the fossil-fuel-fired kilns.”

About 40 percent of the emissions associated with making Portland cement result from burning fossil fuels to create the heat needed to break down limestone, gypsum, and other additives. But the remaining 60 percent or so comes from carbon that’s chemically released from limestone as it breaks down — a process emission that can’t be tackled with alternative fuels alone.

Sublime’s process, by contrast, is one of a number of novel methods, largely coming out of universities, that replace high-temperature cement making completely. We understood that distinction quite quickly, and that’s why we were so eager to test it out,” Tsipis said.

Joe Hicken, Sublime’s vice president of business development and policy, highlighted how the company and WS Development spent months working up to this month’s concrete pour with the companies involved, including primary construction contractor Turner Construction, concrete providers S&F Concrete Contractors, and ready-mix contractor Boston Sand and Gravel.

One of the secrets in the concrete and cement space is that there’s tremendous variability between the products on the market today,” he said. This industry understands that one batch of cement from one supplier may be very different from another batch from another supplier.”

The actual cost of cement production makes up only a fraction of the total cost of deploying concrete in construction projects, Ellis added. Labor is one of the biggest expenses, and anything that disrupts the work of pouring the concrete can dramatically increase those labor costs. Having to tear out and redo a flawed pour is a worst-case scenario.

These are some of the reasons that even the seemingly simplest lower-carbon substitutions to tried-and-true cement and concrete chemistries and processes can take decades to be accepted, Tsipis said. Building is risky enough without trying new building materials.”

On the other hand, once new technologies are proven, they get adopted very quickly,” he said. It’s the industry’s aversion to taking that first step that tends to be a barrier.”

Once those barriers begin to fall, establishing the value of lower-carbon cement and concrete options against the carbon-intensive status quo will become the next significant hurdle, Ellis said. That’s where commitments from the companies that buy or rent buildings and from the government agencies that pay for public works projects will become a major factor, she said.

Private- and public-sector consortiums like the First Movers Coalition need to follow through on commitments to source and purchase low-carbon cement and concrete to create the demand and price signals for scaling up the industry, Ellis said.

Yanni did cover our costs, which was wonderful — that’s what you get from these early adopters,” she said. This was our first commercial project. I’d say we have some time to get down the cost curve.”

When scaled up, Sublime’s electrochemical process can certainly compete on cost with traditional Portland cement production that’s subjected to the same low-carbon demands, she said. Whatever we do will be less than the cost of Portland cement plus post-combustion carbon.”

In that sense, the competitiveness of Sublime’s cement — and the broader push to decarbonize the world’s most abundantly produced material — relies on buyers demanding it. There’s cost — and then there’s price,” she said. And the market will set that price.”

Jeff St. John is director of news and special projects at Canary Media. He covers innovative grid technologies, rooftop solar and batteries, clean hydrogen, EV charging and more.