These scientists bonded over toilet tech. Now they're working on carbon-free cement

Cars and electricity get a lot of attention in conversations about decarbonization, and they should. But building materials like cement and steel also need to be scrutinized.

The production of cement is responsible for about 8% of global carbon dioxide emissions and 5.5% of total global greenhouse gas emissions.

On Thursday, Breakthrough Energy Ventures, Bill Gates' climate finance firm, and DCVC, a Silicon Valley venture capital firm, announced they led a $55 million funding round in Brimstone Energy, a start-up aiming to commercialize carbon-negative cement.

"We need to recognize that cement is a massive problem for climate and that nobody has figured out how to address it at scale without dramatically increasing costs or moving away from the regulated materials that the construction industry knows and loves," Breakthrough partner Carmichael Roberts told CNBC.

Brimstone was founded by two scientists who grew up halfway around the world from each other, bonded in Beijing where they traveled to talk toilets and are now aiming to solve that massive cement problem.

Co-founders Cody Finke and Hugo Leandri overlapped while doing graduate work at the California Institute of Technology in 2017, where they were both working on wastewater treatment. But the pair really bonded when they both attended the Reinvented Toilet Expo in Beijing in 2018.

"We had a lot of fun eating cockroaches in the tourist market and going on runs around Beijing and talking about environmental problems like sanitation and greenhouse gas emissions," Finke told CNBC. They also tried eating snakes, as this photo shows:

Finke, who hails from Seattle, had already worked to develop a solar-powered toilet that was also able to generate hydrogen and electricity, and his CalTech team won $100,000 from the Bill & Melinda Gates Foundation for winning first place in the philanthropic organization's Reinvent the Toilet Challenge in 2012.

He was excited about the idea, but it was expensive to scale.

"I felt like the wastewater technology did a great job at treating wastewater, but to actually save lives, it would need to be deployed. Even with optimistic assumptions, I did not understand how this technology could be deployed as it was just too expensive," Finke told CNBC. "So therefore, the chances of impact were low."

Coming out of the toilet research, Finke started looking at other places to devote his energies. Around that time, David Danielson at Breakthrough Energy Ventures gave a talk at CalTech about heavy carbon emitting sectors that weren't getting much attention from innovators yet. Finke remembers Danielson mentioned steel, cement and fertilizer, to name a few.

Finke used his chemistry knowledge to develop ideas to co-generate clean hydrogen and other commodities, such as sulfuric acid or cement. In 2019, the two decided to be co-founders to develop and commercialize their lab science.

Leandri, who grew up on the French territory of Reunion Island near Madagascar, was somewhat familiar with the cement world because he interned at his father's concrete business.

In 2020, they got $500,000 in funding from the Department of Energy as part of the federal government's ARPA-E, or Advanced Research Projects Agency–Energy, program to continue developing their chemistry ideas.

While neither of them are working on solar-powered toilets now, a core belief of Brimstone comes from their toilet days: Any solution they create cannot just be good for the world; it has to make financial sense for customers in order to make a big impact.

"One of our key criteria at Brimstone is that we believe that in order to be adopted globally, the technology that we're developing has to save people money fundamentally," Finke said.

"We don't know of an example in history where worldwide adoption has gone from lower cost to higher costs. It always goes higher cost to lower cost."

Normally, creating cement involves heating up limestone, which releases carbon dioxide. Even if the energy used to heat up the limestone is 100% clean, 60% of the carbon emissions would remain because of what is inherently in the limestone rock, Finke said.

Some companies are working to make climate-friendly cement by capturing the carbon dioxide and storing it underground or using it. Other companies innovating in the space make an alternate product that serves the same functions as cement but is not cement.

Brimstone's process creates what's known as ordinary Portland cement (OPC), but instead of using limestone, it involves grinding up calcium silicate rock and using a leaching agent to pull out the calcium. Calcium silicate makes up about 50% of the Earth's crust, according to Finke, and is so common that it's often crushed up and used to make gravel. The process is subject to four patents.

Incidentally, the company's name comes from an archaic term for sulfur, which was used in a previous version of its process. "We no longer use sulfur, but we still use stones, and we have a fiery passion for decarbonization," says Finke.

Investors like the company's focus on creating industry-standard cement at a similar or cheaper price point, instead of an alternative that might be more expensive and have to clear new regulatory hurdles.

"Brimstone is the first company we've seen that can make the same exact material that we use today to build our buildings and bridges — ordinary Portland cement – but without carbon emissions and with the potential to cost the same as, or less than, traditional cement," Roberts told CNBC.

That's the key for DCVC, too.

"Brimstone's ability to make actual OPC is essential because over 95% of all cement produced is OPC," Rachel Slaybaugh, principal at DCVC, told CNBC in a statement. "Ergo, no new regulations, material specifications or standards are required. This is a key differentiator from other companies working in the space, all of which are producing a new type of material that is not well-known or understood by the construction industry."

Once cement is produced, it is mixed with other ingredients — known in the industry as "supplementary cementitious material"— in order to make concrete. The chemical process Brimstone has developed to make cement also produces these materials, which "are increasingly in short supply globally and correspondingly increasing in monetary value," Slaybaugh told CNBC.

In legacy cement production techniques, these materials are usually either fly ash, a byproduct of burning coal, or slag, a byproduct of steel production. Burning coal is falling out of favor because of its contribution to climate change, and it's become cheaper and more common to recycle steel, which means there is less slag.

As a byproduct, Brimstone's chemical process also produces a couple forms of magnesium that will react with carbon dioxide and make it into a solid form, pulling it out of the atmosphere.

"Sitting on the ground doing nothing, they will react with carbon dioxide and turn that carbon dioxide into a rock," Finke told CNBC.

Altogether, Brimstone's cement can be carbon negative even if the industrial processes are powered by heat produced from fossil fuels, the company claims.

Brimstone would prefer to avoid fossil fuels for production and use clean heat from companies like Antora Energy, but only when that technology is available at scale and at low cost.

"My view is that, unfortunately, only cheaper things get built and more expensive things do not, so today a clean energy plant would not be financed or built," Finke told CNBC.

Brimstone has its main lab facilities in Oakland, California, and a secondary lab space in Ketchum, Idaho. The 14-person start-up has not yet generated any revenue, and the $55 million funding round will go toward building a pilot plant, which it aims to have operational in 2023.

There's a long road ahead for Finke and Leandri.

But they're driven. Growing up in Seattle, Finke remembers watching Al Gore's "An Inconvenient Truth," and being "devastated" by the idea that Mount Rainier might melt.

"Climate change is something I certainly care very deeply about," Finke said, and working on one spoke of the network of solutions necessary to decarbonize gives him a sense of purpose.