The climate solution beneath your feet

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I’ve come across some pretty wild technologies aimed at fighting climate change. Hydrogen-powered planes, underwater mining robots, and nuclear fusion reactors—each could play a role in cutting down on greenhouse-gas emissions. 

But there are also less glamorous pieces of solving climate change. Take building materials, for example. The world’s most used material, by mass, is cement. And it’s sort of a climate nightmare, responsible for about 8% of global greenhouse-gas emissions. 

The good news is a handful of companies are working to turn around cement’s climate impact. They might not have the pizzazz of a robot, but I’ve been noticing some really fascinating innovations in this field, including some big announcements over the last few weeks. So let’s dive into cement, explore why it matters for climate, and look at the deep technology that might be required to fix this common material. 


Before we get into details, let’s get some definitions straight. Cement is basically glue for buildings. Its job is to bind materials together so we can build things. Cement is mixed with water and sand or gravel to make concrete, which hardens and can be used for buildings or driveways. 

There are two major reasons why cement is such a climate nightmare. The first one is that the process of making it usually involves ridiculously high temperatures, around 1,400 °C. Getting to those temperatures typically requires burning something, usually fossil fuels like coal. Other heavy industries like steel production run into this same problem.

But another major challenge with cutting climate impact of cement comes down to the fundamental chemistry of lime, one of its key ingredients. (Stick with me, I promise this will be worth it!) 

When making cement, usually people start out with limestone, which contains calcium, oxygen, and carbon. To make a material that will react with water and other materials and harden, you need to turn limestone into lime, which is just calcium and oxygen. 

The carbon in the limestone doesn’t end up in the lime—combined with some of the oxygen, it gets released from this process as carbon dioxide, that notorious greenhouse gas. 

If you’re more of the chemical formula type, here’s the breakdown: 

CaCO3 (limestone) + heat → CaO (lime) + CO2 (carbon dioxide)

Making cement this way requires releasing CO2—the greenhouse gases are basically baked into the process. 


One major approach to cutting down on cement’s climate impact is to use less lime. You have to be careful doing this, because you don’t want to end up with cement that’s not as strong or durable as what’s needed. But mixing in a small amount of filler can help cut down on the lime you need to use without compromising performance. 

One interesting approach to the mix-in method comes from CarbonCure, which adds some CO2 to concrete as it’s mixing. The CO2 reacts with ingredients in the mixture and hardens, a process called mineralization. 

You’re basically doing the opposite of the cement-making process that I described above—adding the CO2 back in. Doing this in a controlled way can help trap some CO2 while also cutting down on how much lime you end up using in the final product. (For more on CO2 mineralization, check out our story from last year on a facility that’s doing a similar process underground). 

Last week, CarbonCure announced that it had made cement using CO2 that had been pulled directly out of the atmosphere, a process known as direct air capture. For the demo, CarbonCure added CO2 into some wastewater that otherwise would have been too reactive to reuse. 

For the demo, CarbonCure partnered with a California-based startup called Heirloom that captured the CO2, and the companies say it’s the first time CO2 captured from the atmosphere has been used to make cement. 

This process is really small-scale right now, and there are a lot of questions about whether direct air capture can be done cheaply and efficiently. But CarbonCure’s approach could help shave off some of the climate pollution that goes into building while also helping to clean up emissions already in the atmosphere. 


Other groups are trying to reinvent cement from the ground up. 

I recently spoke with Yet-Ming Chiang and Leah Ellis, the duo behind Sublime Systems, a Boston-based cement startup that recently raised $40 million in funding. Both Chiang and Ellis have a background making batteries, and they’ve decided to use their skills to rethink cement. 

Remember those two reasons I said cement is so bad for the climate, the heat and the chemistry? Sublime is trying to go after both of those. 

First, they’re trying to replace the heat in the cement-making process with electricity. In work at MIT, Chiang and Ellis discovered that they could transform limestone to lime without high temperatures or fossil fuels: they were able to do similar reactions using electricity. 

If that electricity comes from renewable sources, Sublime could cut emissions from cement by 70%. 

As for the emissions baked into cement’s chemistry, there are a few possible solutions. First, Ellis explains, the CO2 coming from their process will be easier to capture and either use or store, since it will be concentrated and relatively cold. That means they wouldn’t need all the expensive equipment typically used in carbon capture and storage systems. 

Their process could eventually also use other starting materials, including some that don’t contain carbon, so they wouldn’t produce CO2 at all. 

There’s a long road ahead for Sublime or any company working to reinvent heavy industry. “It’s going to be hard,” Ellis says. “We’re not doing this because it’s easy.”

Today, the company’s facility can make about 100 tons of cement per year. To compete on cost, Sublime will need to make cement at the same scale as commercial plants, which can produce about a million tons of cement each year. Sublime is planning to reach that goal in 2028. 

If you’re interested in digging more into the challenges of heavy industry for climate change, here are some stories from our vault: 

hand holding a cylindrical nuclear cooling tower with steam escaping out the top


Another thing

Bigger isn’t always better when it comes to nuclear power. A new movement to shrink nuclear reactors could simplify the process of getting them built … in theory. The problem is, these so-called small modular reactors (SMRs) have been in the works for nearly two decades. 

Finally, one of the leading SMR companies has cleared one of the final regulatory hurdles to building its reactors in the US. So what will it really take to reinvent nuclear power? Check out my story on the topic to find out.

Keeping Up with Climate

Pet food can come with a high emissions price. Alternatives might reduce our furry friends’ climate impact. (Bloomberg)

Setting a goal of keeping global warming below 1.5 °C was pretty arbitrary. The fact that this goal is slipping out of reach is still significant. (The Atlantic

China has built the world’s largest EV charging network. A couple of keys to the technology’s success have been government subsidies and standardized technology. (Grid

→ Here’s where all the fast chargers in the US are located. (MIT Technology Review)

Europe is following climate legislation in the US with its own “Green Deal Industrial Plan,” which includes $270 billion in spending. (Grist

→ Here’s what’s in the US plan, which passed last year and includes $370 billion in spending. (MIT Technology Review

→ Some of that money is for individuals: here’s a guide for how you can get in on the action. (New York Times

Speeding up approvals for energy projects could help fast-track renewable energy. So what’s with the drama about permitting reform? (Inside Climate News)

Global electricity demand is still rising every year. The good news is that renewable sources are set to cover almost all of that increased demand. (International Energy Agency)

From paying people to use less electricity to harnessing their batteries, these startups are helping homes help the grid. (Canary Media

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