The high-stakes race to reduce emissions from cement

“If we’re successful, this could be a way of making cement for millennia to come,” said Leah Ellis, chief executive of Sublime Systems, an MIT spinoff that has raised nearly $50 million and is developing plans at its labs here to produce a million tons a year of emissions-free cement.

The manufacturing of cement, a flour-like substance that becomes concrete when mixed with sand, gravel, and water, was responsible last year for nearly 2.8 billion tons of carbon dioxide — more than triple the amount of carbon pollution from global aviation, according to the CICERO Center for International Climate Research in Norway.

Emissions from cement have more than tripled since the early 1990s, and they’re now responsible for roughly 7 percent of all global carbon emissions.

Without significant changes in how cement is produced, the resulting pollution could increase substantially over the coming years as more countries, such as China and India, develop at a rapid pace. To comply with the Paris climate accord, cement emissions must fall by at least 16 percent by the end of the decade, scientists say.

Those opposing forces, and the urgency to reduce the pollution, has led Sublime and scores of other companies to seek novel ways of creating cement that either doesn’t produce carbon emissions or reduces them. It’s a potentially lucrative race to a solution that can’t come soon enough.

Sublime plans to develop large amounts of cement without using traditional methods, which involve depositing a mix of limestone and clay into giant kilns and using fossil fuels to heat them up to about 2,500 degrees. That process creates something called clinker, a binding agent, by stripping carbon dioxide from the limestone. The clinker is then ground into a fine powder and mixed with other materials, such as gypsum, to make cement.

For every ton of clinker produced, about 1,300 pounds of carbon dioxide is released into the atmosphere. More emissions come from cooling the kilns and transporting the cement.

The company, based here at the climate-tech incubator Greentown Labs, plans to build cement plants in the coming years that don’t use limestone or require high temperatures. They plan to replace the kiln with an electrochemical process that extracts the key ingredients of cement from a range of minerals in igneous rocks at room temperatures, using renewable electricity.

“I think that their approach is very promising,” said Randolph Kirchain, a research scientist who serves as director of MIT’s Concrete Sustainability Hub, which for more than a decade has sought solutions to reduce carbon emissions from cement and other building materials.

Other companies seeking to reduce emissions from concrete — the most widely used human-made material on the planet — have taken different approaches.

Fortera, a California-based company that has raised more than $35 million and is now building its first commercial plant, says its manufacturing process captures large amounts of carbon dioxide from the kilns in traditional cement plants and uses that to create a new kind of cement that releases 60 percent fewer emissions per ton while it’s being made than ordinary cement.

“I am very confident that we can have a meaningful impact on CO2 emissions,” said Ryan Gilliam, who cofounded Fortera four years ago with the goal of enabling the cement industry to effectively eliminate its carbon pollution by 2050.

Another California company, Blue Planet, has similar technology that seeks to mineralize the carbon dioxide produced by cement manufacturers to create synthetic limestone, a kind of rock that can be used in concrete. They say their technology could eventually help trap billions of tons of carbon dioxide.

CarbonCure Technologies, based in Nova Scotia, is taking another route, seeking to inject the emissions from a range of industrial plants into concrete while it’s being mixed, effectively locking it into the cured stone and keeping it from the atmosphere. It has been licensing its carbon-injection equipment to concrete producers around the world, with a goal of preventing nearly 500 million tons of carbon dioxide from entering the atmosphere every year.

“We’re picking up [the] pace and hoping to see our technologies used across the 125,000 concrete plants around the world,” said Robert Niven, the company’s chief executive, noting that more than one-third of the nearly 300,000 tons of carbon they say their technology has prevented from being released into the atmosphere took place in the past year.

But with more than 4 billion tons of cement produced every year, and the world’s building stock expected to double by 2060, some have raised concerns about banking on new technology and ambitious claims about long-term goals — especially for an industry bound by strict building codes and liability concerns about weakened, less-reliable structures.

There have been some changes over the years in how concrete is produced, but those changes have come slowly, requiring strict regulatory scrutiny, and haven’t made a major dent in overall emissions.

“It’s a conservative, risk-averse industry,” said Pritesh Gandhi, who oversees digital transformation at Holcim, a Swiss-based company that’s among the world’s largest producers of cement. “This industry is full of very technically oriented specs and testing methods.”

He and others noted how the industry has incorporated different additives, such as byproducts from burning coal and making steel, that reduce emissions from what’s known as ordinary Portland cement. But that came after years of testing to ensure the concrete would be sufficiently durable to stand up over time and through harsh weather and other stresses.

Any ordinary cement substitute must also be sufficiently competitive economically.

Officials at Boston Sand & Gravel Co., the area’s largest concrete producer with more than 60 trucks pouring thousands of yards of concrete a week, said there’s an increasing demand for concrete blended with additives that can reduce emissions during the manufacturing process by as much as 20 percent below the ordinary mix, even though it can be more expensive. (Costs depend on the size of a project and other factors.)

“Costs are definitely a concern,” said Jim Carreira, technical director of Boston Sand & Gravel, which is based in Charlestown.

Still, more of Boston Sand’s clients have been seeking environmental product declarations, a kind of nutrition label on their concrete, that outlines its “global warming potential.”

Carreira supports efforts to reduce the industry’s emissions with new technology and mixes, but he has concerns about their ultimate viability.

“We deal with some harsh elements,” he said. “We need to be shown, through trials, that we can check all of those boxes. There’s always concern, until it’s proven.”

In Massachusetts, which has a law requiring the state’s overall emissions be reduced 50 percent below 1990 levels by the end of the decade and effectively eliminated by 2050, there are no requirements that developers use lower-emissions concrete.

But state lawmakers have proposed bills that would encourage that.

One bill proposed by Senator Cynthia Creem, modeled after laws passed in New Jersey and Maryland, would require state building projects to use lower-emissions concrete. It would also direct officials to come up with state incentives to encourage the wider use of such blended forms of concrete. The bill has yet to have a hearing, but last legislative session, a similar version was reported favorably out of the Joint Committee on State Administration and Regulatory Oversight.

State environmental officials declined to comment on whether they support Creem’s bill or similar legislation.

But they noted Massachusetts is already taking part in a federal-state agreement that aims to promote the use of lower-carbon concrete and other building materials. Moreover, they said, the Massachusetts Clean Energy Center this month plans to start providing financial and educational support to prod the state’s concrete plant owners to publish environmental product declarations.

On a recent morning at Sublime’s labs in Somerville, where the growing staff in white lab coats and safety glasses was churning out more of their bright white powder, Ellis said she was confident her company could achieve its goals of creating a product that’s competitive in price and as durable as ordinary cement.

The company, she said, can now produce 100 tons a year of its cement and aims to be able to manufacture one million tons annually within five years. It plans to use Dracula’s Coffin — a stainless steel, casket-shaped freezer — to help prove the durability of its product by repeatedly freezing and thawing it.

The company’s cofounder, Yet-Ming Chiang, a professor of materials sciences at MIT, said he is optimistic Sublime could succeed.

“What we’ve found is that we can bring tools from our technical training to these problems, and use them in new and creative ways,” said Chiang, a serial entrepreneur who also founded companies including 24M Technologies, A123 Systems, and American Superconductor Corp. “I believe it’s a very fertile time for this kind of reinvention.”

David Abel can be reached at david.abel@globe.com. Follow him @davabel.