This story aired on the July 9, 2024 episode of Crosscurrents.
We know that cars and planes and even landfills contribute to climate change, but there’s another big source of planet-warming gasses. It’s all around us, it might even be around you right now as you listen. We are talking about concrete and the cement used to make it.
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San Francisco’s Laurel Village neighborhood is usually pretty sleepy, but on this summer morning, a small army of hard-hatted construction workers is pounding nails and welding metal inside a three-story steel frame – they’re working on the expansion campus for University High School.
I'm here to learn about something foundational to this building, like literally the foundation. The concrete. And that’s the domain of Michael Smith, director of construction with Truebeck, who tells me more.
“So the concrete is provided by Central. Central is a Northern California ready mix supplier. They have a batch plant that's supplying this job that's down in the Dogpatch area of San Francisco,” he says.
Concrete has three main ingredients: Cement, water, and aggregate, which is a mix of gravel and sand. It’s possible to source all of those ingredients in California, but it’s not as easy as it used to be. The last Bay Area cement plant, Lehigh, closed in 2023.
“The cement comes from China, the aggregate comes from some quarries in British Columbia and that's brought via barge,” Mike tells me.
Those ingredients then make their way to Central or one of a handful of other Bay Area concrete suppliers. Then they’re mixed up and funneled into trucks that stream in and out of job sites like this one. And at similar sites all over the world, every day. Concrete is the most widely consumed man made material on earth. It’s also a huge driver of climate change, as Cody Finke, CEO and co-founder of Brimstone, tells me.
“If you talk about greenhouse gas emissions – which is more than just CO2 – then cement and concrete are about 5.5% of global greenhouse gas emissions. If you just talk about CO2, it's like 7 or 8% of CO2 emissions,” he says.
And to put that 7-8% of global carbon emissions in context, it’s roughly equal to CO2 emissions from all cars.
And you might think what drives concrete’s emissions is all that shipping of ingredients from far-away places. But actually, just one of those ingredients is the big culprit. The cement.
“Without cement, concrete is just a pile of wet, sandy gravel,” Cody explains. “But cement is actually what gives the concrete structure. It's also responsible for about 90% of the greenhouse gas emissions associated with producing concrete.”
So I’m here at his company’s lab to learn how Brimstone is trying to fix that problem, by making cement without the CO2.
Inside the lab
Brimstone’s R&D space looks like a chemistry lab crossed with a commercial kitchen and a very clean automotive garage. In the back, baseball-sized rocks are crushed in one machine, filtered in another, and further pulverized in a third. A chemical agent is added. And to me, it just looks like a slurry. You can’t see how it’s different or special, but it is. And that’s where the important science comes in.
“Cement is a calcium-based material,” Cody says. “And where we get calcium today is a rock called limestone.”
But in addition to calcium, limestone contains a lot of carbon dioxide. And when you heat the limestone to make cement, that CO2 is released. That’s the first source. The second source of CO2 is from the energy that goes into heating the rock. You could use renewable energy to generate that heat. But that would only erase 40% of the total CO2 emissions.
“So even if you were to use 100 percent clean energy to make cement via the conventional way, the majority of the emissions would still persist,” Cody says.
So Brimstone’s answer to that problem is to make cement out of a different material that doesn’t contain CO2. The company uses another rock that is globally abundant – far more abundant than limestone, in fact. Calcium silicate.
This is not exotic stuff, but importantly, it does not contain carbon dioxide, which Brimstone wants to avoid. While it does, as the name implies, contain calcium, which Brimstone wants. Granite and basalt are examples of calcium silicates.
Back in the lab, the silicate slurry is mixed with a few other ingredients and heated to form a cement that works just like limestone cement – in fact, last year, a third party certified that Brimstone's cement meets the ASTM standards needed to prove it. And that's really important to ensure industry acceptance.
The last step is to test the strength of small cubes made with the Brimstone cement, to measure its strength. As you can imagine for a key ingredient in concrete, its strength is a key attribute.
These cubes are small… roughly the size of children’s building blocks. Looking at these, and then trying to imagine how much concrete goes into something like the Bay Bridge… It made me realize: Brimstone still has a long way to go. It has resources on its side. The startup raised over $60 million in venture capital. And that was before landing a huge grant from the Department of Energy this spring. That award – $189 million – is part of a big push to support efforts to decarbonize a bunch of industries, including steel, chemicals, and food production.
Brimstone’s next step is to build a pilot plant in Reno, Nevada, in order to scale up production.
Still, Brimstone is trying to break into a very old established industry. If they can successfully scale up production, then comes the question: will anyone use their cement? That's largely up to another player that we haven't talked about yet: designers and architects.
Designing for better concrete
To learn more about this part of the effort to combat concrete’s carbon problem, I meet with Frances Yang. She’s a structures and sustainability specialist in the San Francisco office of the design and engineering firm ARUP.
ARUP has worked on lots of concrete-heavy Bay Area projects including the San Francisco International Airport and the city’s Museum of Modern Art. And Frances has been pushing for new standards and laws aimed at climate innovations in building materials. She says companies like Brimstone face a classic chicken and egg problem.
New entrants “need the demand to secure the financing to scale,” she tells me. But when you’re only making small samples of your product, it’s hard to create enough of that demand from customers, because those builders “want to see examples of it in use and successful at scale that they're building.”
And even if Brimstone can secure customers, building up their manufacturing capability will take time.
Fortunately, less carbon-intensive concrete already exists. It’s not as clean as Brimstone’s. It’s more the middle ground, and it’s actually been available for a while. To make it, suppliers put less cement into their concrete mix and compensate for that, with other materials that can do the same job, without all of the emissions.
There are some examples of this type of concrete in the Bay Area. It’s in the eastern span of the Bay Bridge, and in the foundations of the Cal Academy of Sciences and the San Francisco Federal Building.
And it’s what's getting poured over at the University High School campus in Laurel Village.
When I go back there for a second visit, a truck is pumping the wet concrete through a wide hose up to the second floor, where about 15 men are moving fast to cover and smooth it out over a grid of rebar. It’s like a choreographed dance.
Truebeck’s Mike Smith, who leads the concrete team, tells me what’s happening.
“So, we are pouring a cement replacement and low carbon concrete for all the foundations, walls and slabs.”
This concrete has up to 50% lower global warming potential compared to conventional concrete. Of course, this lower carbon option is still reliant on an exceptionally high-carbon industry, coal-fired power plants.
“The fly ash is a byproduct of the coal power plant industry. And it is brought via rail from, uh, New Mexico, Arizona, Utah…” he explains.
And those sources are drying up, as coal plants close.
But that’s going to become less of an issue over time. Eventually, this type of lower-carbon concrete won’t make the cut. California legislators passed a bill in 2021 that could mandate zero-carbon concrete by 2045. That will give a leg up to manufacturers like Brimstone – so long as they keep grinding rocks into cement that’s easy on the climate.
