Concrete Is Awful for the Planet. Clever Chemistry Can Help

Without it, our civilization would be nowhere. With it, the Earth is suffering. But what if concrete could be used to store climate-warming carbon?
Illustration of Earth shattering from a concrete layer
8%: The portion of global carbon emissions produced by the cement industry.Illustration: Jan Siemen

If you find yourself at this moment in a city of any size, take a look out the window. Most of what you see is made with a single material, one that dominates our world: concrete. It makes up the bulk of virtually every office tower, shopping mall, highway, and airport on Earth. We produce tens of billions of tons of the stuff every year—enough to build a 100-foot wall right around the equator. And that tonnage is certain to grow in coming years, as cities continue to mushroom in China, Nigeria, and other fast-developing nations. Concrete is wonderfully useful, but it comes at a steep cost: The industry that makes it eructs about 8 percent of all annual carbon emissions.

To be precise, it's the production of cement—the glue that binds together sand and gravel to form concrete—that is the problem. Or, rather, two problems. To make cement, you put limestone and other minerals in a kiln and bake them at up to 2,700 degrees Fahrenheit. Problem one: The heat for those kilns is typically generated by burning coal or other fossil fuels. Problem two: The heat-generated chemical process that eventually results in the fine gray powder we call cement also generates gaseous carbon dioxide as a byproduct, which gets whisked up into the atmosphere.


Illustration: Alvaro Dominguez

Those emissions add up. If the cement business were a country, it would be the world's number three producer of greenhouse gases, trailing only China and the United States. No surprise, then, that researchers and entrepreneurs around the world are working on projects to make cleaner concrete. The most promising are a handful of companies that focus on making the process of manufacturing concrete not only less of a problem but part of the solution.

The current head of the pack is a company named CarbonCure Technologies. It aims to change the chemistry of that sea of concrete slightly but significantly. Headquartered in an aluminum-sided, two-story building in a modest industrial park outside of Halifax, a tiny city dangling off Canada's Atlantic coast in a time zone an hour east of Eastern, CarbonCure's entire staff could fit in a school bus. At the helm is a lean, amiable, 42-year-old engineer named Robert Niven.

Niven grew up on Vancouver Island, with regal forests and rocky beaches for playgrounds. During summers home from college, he worked as a firefighter in British Columbia's remote northern forests and spent as much time as possible rock climbing and whitewater kayaking. As a civil engineering student at Montreal's McGill University in the mid-aughts, he fell into a research program aimed at figuring out how carbon could be used to help make concrete, replacing some of the cement used in the process. The concept wasn't new, but no one had figured out how to do it effectively at scale. Niven looked at the problem through a chemist's lens, researching exactly how it might work at the atomic level.

A year before he graduated, Niven went to a UN conference on climate change in Montreal. He was dazzled by the energy of the 10,000 attendees who swept into the city. But what really hit home was a speech by a representative from Tuvalu, a tiny Pacific island nation. “He gave the most emotional plea for help, saying, ‘We're losing our history, our homes, our livelihoods, and our ancestry because of sea level rise,’ ” Niven says. Suddenly his work felt like something more than just a math problem.

Two years later, Niven moved to Halifax to be with his then-girlfriend, now wife. Her father happened to be a successful entrepreneur with a penchant for niche green projects, like solar-powered marine lights, and he helped Niven see how his ideas could be turned into a business. With that advice—and a little cash—from his future father-in-law, plus $10,000 in leftover student loans, Niven launched CarbonCure in 2007. The concept: develop a system to replace some of the cement used in making concrete with carbon dioxide, thereby both reducing emissions and sequestering carbon. Not to mention saving money.

A Better Build

by Liz Stinson

Concrete dominates construction, but some eco-friendly materials are trying to chip away at the edges.

Cross-Laminated Timber

Made from lumber boards that are glued and layered on top of each other crosswise, CLT comes in giant panels that can replace concrete and steel as the backbone of a building. When produced with sustainable forestry practices, CLT is a green alternative. The material was used to construct what is currently the world's tallest timber building: Norway's 18-story Mjøstårnet tower.


Combining the cannabis strain's woody interior pulp with lime and water produces “hempcrete,” a drywall-like material that's light and robust and has a low carbon output. Hempcrete isn't load-bearing, so it won't replace concrete and steel, but it's already been used in residential projects for walls and insulation.


When the threadlike fibers of mushroom root extensions are mixed with byproducts like corn husks, sawdust, and rice straw, it creates a foamlike material that can be cast into panels, bricks, and tiles. Often used to replace Styrofoam packaging, mycelium materials have also been used to make acoustic panels and insulation. One architecture firm in Cleveland is experimenting with combining mycelium with wood, insulation, and other construction waste to create biodegradable bricks.

Niven and his team eventually figured out a process that takes liquefied CO2 (captured from places like ammonia and ethanol plants) and injects it into wet concrete as it's being mixed. The CO2 chemically reacts with the cement and other ingredients in the mix, remineralizing it into solid calcium carbonate, which helps bind the other ingredients, increases the concrete's compressive strength, and takes the place of some of the cement that would otherwise be required. And even if the concrete eventually gets pulverized, that carbon remains an earthbound solid.

The company has developed a surprisingly simple system to bring the whole process out into the field. A tank of carbon dioxide feeds into a pair of dorm-fridge-sized metal boxes stuffed with valves, circuitry, and telemetry gear, which regulate the carbon dioxide's flow into a hose, which sprays it into the mixing drum. (The boxes are all made by a few guys in jeans and T-shirts at the Halifax HQ.) The tricky part is figuring out the optimal dose of CO2 for different mixtures; the strength, weight, and appearance of concrete for an airport runway in northern Canada are not necessarily what you want for an office building wall in Southern California. At the Halifax headquarters, CarbonCure technicians keep an eye on a wall of monitors tracking the operations of every one of their machines out in the real world. The monitors let them know if, say, a valve gets blocked at a job site in Georgia or a tank starts running low in Singapore.

The simplicity of its system is one of CarbonCure's best selling points. The concrete makers who are its customers don't have to change much for mixing and pouring at a construction site—they just add a little extra hardware. “The whole system fits in a crate,” Niven says. “It takes a single day to set up and it's universally applicable to any concrete plant in the world.” CarbonCure also connects clients to suppliers of captured carbon from other dirty manufacturing processes. (The company's goal is to someday capture carbon from cement plants themselves.)


CarbonCure's tech has improved steadily over the years, and so has its profile. In 2018 the company was named one of 10 finalists for a $20 million XPrize for turning carbon into commercial products. (The contest's winner will be announced this fall.) That same year, the company got a sizable (Niven won't say how sizable) investment from Breakthrough Energy Ventures, the billion-dollar fund focused on carbon-reducing investments backed by Bill Gates and other tech titans. The money helps, Niven says, but the stamp of approval is perhaps even more valuable. “It really meant something for the broader investment community that that group would say, ‘This one's a vetted winner,’ ” Niven says.

Today CarbonCure says that more than 200 concrete makers across North America and in Singapore are using its system. A new building on LinkedIn's Silicon Valley campus, a stretch of road in Hawaii, and an aquarium exhibit in Atlanta all include CarbonCure-treated concrete. Its technology has been used in the making of more than 4 million cubic yards of captured-CO2 concrete, saving some 64,000 tons of emissions, according to the company.

But in the big picture, CarbonCure's impact is still pretty small. In a few cases, customers have been able to reduce their cement use by 20 percent—but the average is closer to 5 percent.

The best news, then, may be that CarbonCure has a growing crowd of competitors, including three of the other finalists for that XPrize. One rival, New Jersey-based Solidia, uses a similar concept and seems to get even better results, but as of February, it makes only prefabricated concrete blocks. (The construction industry mostly uses concrete mixed at job sites.) Another, Alberta's Carbon Upcycling Technologies, combines gaseous CO2 with fly ash—a waste product from coal-fired power plants—to create nanoparticles that can replace about 20 percent of the cement in a concrete mixture. Cofounder and CEO Apoorv Sinha says he hopes to eventually double that percentage, and to start selling to his first customers this year. Meanwhile, researchers at Rice University claim to have developed a concrete mix that primarily uses fly ash as the concrete binding agent—no cement required. Other outfits are attacking the problem from different angles. A group of MIT scientists and an Australian company are developing new, lower-emission ways to make cement powder.

Most of these projects haven't made it to market. Securing funding is difficult, and the customer can be too. The construction industry is notoriously chary about adopting new ways. With good reason: You can't afford to “fail fast” or “iterate on your product” when your product is a skyscraper or a dam. To truly decarbonize all that concrete will probably take some kind of government help to make these methods more commercially attractive. But CarbonCure's success offers a proof of concept: There's a concrete business case for better cement.


VINCE BEISER (@VinceBeiser) is the author of The World in a Grain: The Story of Sand and How It Transformed Civilization. His last story for WIRED, in issue 28.01, was about catfishing from prison.

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