Every year, the world uses an estimated 10 trillion kilograms of concrete. Nearly every major construction project makes use of the stuff. It’s in everything from office buildings, dams, bridges and sewers to sidewalks, home foundations, patios and birdbaths. And our use of it is only projected to climb. According to the United Nations, the world is on track to build more than 230 billion m2 of new buildings by 2060—equivalent to the city of Paris again every week—and those new buildings will largely be made of concrete.
People say concrete is the world’s most-used material, after water. But lately headlines have also declared it to be “the most destructive material on earth.”
We produce around four trillion kilograms of concrete’s most important ingredient—cement—annually, enough for roughly 450 kilograms per person. That global production has been estimated by the International Energy Agency to contribute as much as 7 per cent of global carbon dioxide emissions. This is roughly three times more than the entire global aviation industry.
This outsize contribution to climate change has prompted something of a mad dash in recent years to turn concrete from grey to green. Companies are making bold claims in response to questions about the industry: that they can reduce the carbon footprint of one of the world’s worst emitters. That the literal building block of cities can be composed, at least in part, from carbon dioxide emissions. That concrete could even become carbon negative—that is, your cinder block wall or poured foundation could ultimately contain more CO2 than was emitted in its production. These bold claims are increasingly being tested in Alberta.
Most Albertans—and countless visitors to our province—are familiar with the seemingly anachronistic industrial complex and strip mine on the north side of Lac des Arcs, some 15 minutes east of the entrance to Banff National Park. But you might not know that this collection of drab grey towers near the foot of Grotto Mountain is Lafarge’s Exshaw facility, which happens to be Canada’s largest cement plant.
Imagine concrete as a kind of hard cake made by mixing water and sand with a flour made primarily from powdered limestone (calcium carbonate), a type of sedimentary rock obtained by mining. This—limestone—is what Lafarge is quarrying at Exshaw. The plant then uses a giant rotary kiln to heat the limestone, along with a few other ingredients such as slate, to very high temperatures—typically 1,450°C. The result is clinker: rough grey lumps 2–3 cm in diameter, the main ingredient of cement.
“Cement production turns out to be the issue,” says Gaurav Sant, a professor of engineering at UCLA who has extensively researched the carbon intensity of concrete. This first stage in making concrete is a major component of the material’s giant emissions footprint. Indeed, “cement production is one of the most energy-, materials- and emissions-intensive industries on earth,” Benjamin Israel, senior policy analyst with the Pembina Institute, tells me. “If the cement industry were a country, it would have the third-largest emissions, just after China and the US.”
“There are only so many levers we have in a cement-manufacturing process to reduce [our] carbon footprint,” says Jonathan Moser, Lafarge’s head of environment and public affairs. Firing a cement-plant kiln requires burning vast amounts of fossil fuels, so switching to lower-carbon energy sources is a must. Moser says the Exshaw plant—where cement has been produced for over a century—has already started such a shift, using $10-million from Emissions Reductions Alberta (ERA), a provincial agency that accelerates the development and demonstration of emissions-reducing technologies. (The money was part of roughly $70-million distributed to 10 projects in 2019, funded in part by the now-defunct provincial carbon tax.)
Lafarge is now using a variety of alternative fuel sources at Exshaw, including construction demolition waste (treated wood and shingles), used carpet, non-recyclable plastic, and old tires, sourced from a waste processing facility in Calgary. The company estimates that every 20 per cent reduction in its natural-gas use and replacement with lower-carbon fuels translates to nearly 75,000 fewer tonnes of CO2 per year, or the equivalent of 16,000 cars’ annual fuel use. It says that by later this year it will have replaced 30–50 per cent of its fossil fuel use, and by 2030 will be producing up to 40 per cent less net CO2 per tonne of cement. Ongoing research from Lafarge partners—the University of Calgary, Queen’s University and the Pembina Institute—will measure the environmental footprint of sourcing and using alternative fuels, as well as the benefits of diverting material from landfills, which emit methane (a particularly potent greenhouse gas). The company will also monitor air quality in the Bow Valley, but predicts “minimal changes.”
Research from the Pembina Institute has found that cement plants in western Canada have traditionally used less “alternative fuel” than cement plants in other countries, largely because conventional (fossil) fuels were so cheap here and local landfill costs so low. Alberta’s carbon price on large industrial emitters and rising landfill costs have helped changed the equation. Pembina identified 29 potential alternative fuels all told, including livestock waste (e.g., bone meal), drilling waste (e.g., contaminated mud) and wood waste, all in aid of reducing cement’s GHG emissions.
But even if all cement were produced using completely renewable energy, the industry still releases an inordinate amount of carbon. That’s because anywhere from 50 to 70 per cent of the carbon footprint of cement currently comes not from the fuels used to facilitate the process but from the release of carbon dioxide from limestone. The heating of calcium carbonate results in a calcination reaction, which means large quantities of carbon dioxide that have been trapped for millennia escape. To meaningfully reduce industry’s impact, then, the composition of concrete itself must change.
The technology is innocuous in appearance, much like the everyday product it’s trying to improve. In Calgary, a large green canister sits on a trailer at a new provincially owned facility called the Alberta Carbon Conversion Technology Centre (ACCTC), right next to the Shepard Energy Centre, a city-owned power plant. Calgary-based Carbon Upcycling Technologies installed the technology. The company’s business development coordinator, Madison Savilow, describes the canister as a “one tonne per day reactor,” and says it will be used to create greener concrete.
In an effort to significantly reduce its CO2 emissions, the industry is trying to offset the amount of cement needed in concrete production. In other words, the less “flour” used in the recipe, the less limestone that must be broken up and heated to very high temperatures, and the smaller the emissions footprint of the eventual concrete “cake.”
And that’s where things get interesting. Many companies and researchers are now showing that the amount of cement needed can be reduced by adding a form of CO2—that is, the end product we’re trying to avoid can actually become an ingredient of concrete, literally “cementing” GHG emissions into the hard slabs we use to build infrastructure. “For a long time the cement sector has been considered extremely difficult to decarbonize,” the Pembina Institute’s Israel says. The latest innovations, he says, are exciting. “They’re actually moving the needle.”
Such technology reflects new thinking. “We view carbon dioxide as something we can use as a resource, rather than as a liability,” Savilow explains. Indeed, that’s the raison d’être of the ACCTC as well, says Brent Scorfield, senior business partner with InnoTech, the provincial research centre that opened the $20-million facility in 2018 and now runs it. Their goal, he says, is to “convert CO2 as a waste material into a value-added product”—to make it into a “feedstock” for companies such as Carbon Upcycling.
In its essence, what’s happening at the ACCTC isn’t all that complicated. “We take CO2 in a gas form and sequester it into inorganic solids in a powdered state,” explains Savilow. That powder then reduces the cement needed in Carbon Upcycling’s concrete recipe. The source of that CO2 is the adjacent Shepard plant itself, which pipes over flue gas—the emissions from burning natural gas for electricity, containing 5–7 per cent carbon dioxide—that would otherwise go up the stack and into the atmosphere. Some 25 tonnes of CO2 are now being sent to the ACCTC every day, where it’s “captured” and concentrated.
These days Carbon Upcycling is enhancing fly ash—a grey, powdery by-product of coal-burning often used in concrete production—by mixing it with solid CO2. This “super-ingredient” reduces the carbon intensity of the finished product. Savilow says Carbon Upcycling’s research suggests a 70 per cent market uptake of their enhanced fly ash would amount to a 1 gigatonne reduction in carbon dioxide emissions each year. But she says the company’s new concrete is proving stronger (with 30 per cent more “compressive strength”) and cheaper too.
This is a critical point. Sant from UCLA emphasizes that if “greener” concrete is not equivalent or better than conventional concrete—and at least as cheap—it won’t be used much, and thus its environmental testimonials will ultimately amount to very little.
But Carbon Upcycling isn’t alone in thinking that “greener” concrete can prove economic. The ACCTC was created to serve as a host to a global competition, the acronym-ridden NRG COSIA Carbon XPRIZE, which “challenges the world to reimagine what we can do with CO2 emissions by incentivizing and accelerating the development of technologies that convert CO2 into valuable products.” Five of the 10 finalists for the US$20-million-dollar prize will test and demonstrate their technologies at the Centre in 2020.
CarbonCure is one of the other Calgary-based XPRIZE finalists. The company was created by engineer Rob Niven in 2007. Niven says he began to grasp the severity of the climate crisis during the years he spent fighting forest fires in BC. That’s where he became intimately aware that the “climate was changing and you don’t need to look very far” to see its effects.
Today, CarbonCure takes liquid carbon dioxide—captured from plants such as the Dow petrochemical complex in Fort Saskatchewan—and converts it into a mineralized, solid form that can be incorporated into concrete. The company has already installed its system, consisting of a silver stainless steel tank full of liquid carbon dioxide and two boxes, at seven concrete plants in Alberta, including Lafarge Winterburn in Edmonton. When that facility shut down for the day, CarbonCure fired up its system. “They were up and running” the next day, Niven says.
So far, CarbonCure’s technology reduces the amount of cement needed in concrete by 5–10 per cent, Niven says, which means, for the average concrete plant, a “CO2 benefit in the order of about 1,000 tonnes a year.” The company’s new “cake mix” was recently used for Canada’s largest carbonated-concrete pour, at Calgary’s airport. “Alberta has more activity happening in [carbon] utilization than probably anywhere else in the world,” he says.
Niven hopes Alberta’s carbon experiments resonate widely. “Concrete has such an important role globally, because it’s one of the very few products that you can [sink mineralized CO2 into] permanently,” he says. “But it’s emissions are so high,” Niven adds, and it’s so widely used that even small improvements “actually make a really big difference.”
Lafarge’s Moser envisions a future where technologies such as Carbon Upcycling’s and CarbonCure’s helps his company achieve what he calls “the perfect circular-economy story”—low-carbon fuels making a low-carbon cement that uses CO2 captured from flue gas and sequesters it in building materials. “That’s the ultimate,” he says.
But Niven sees an even more ambitious future, where concrete could itself be a man-made carbon sink. “I believe concrete can be a main solution for climate change,” he tells me. “It can incorporate a number of carbon-reduction technologies that allow it to even go negative.”
The promise of a concrete product that actually contains more CO2 than was emitted in its production may be bold, but it has attracted a lot of attention lately—and public money. Locally, much of that comes from ERA. The not-for-profit agency, which began operations in 2009 under Ed Stelmach’s PC government, has been funded through various emissions-levy schemes that have changed with governments: most recently, Jason Kenney’s Technology Innovation and Emissions Reduction program. ERA received $158-million from the government of Alberta over the last four years, and used it to co-fund all manner of emissions-reduction technologies, including those targeting concrete.
Mark Summers, ERA’s executive director for technology and innovation, says his agency’s goal is “to both reduce greenhouse gas emissions and grow Alberta’s economy.” Shrinking the construction industry’s eco-footprint, Summers says, is a “critical strategic area for Alberta.” ERA is funding research into technology that could conceivably be used to justify the ongoing growth of fossil-fuel-sector emissions—because some of that industry’s carbon could be captured and used by other sectors. This may explain why even Kenney’s UCP government supports ERA’s work. Last November, Environment Minister Jason Nixon announced a $5-million ERA prize would be given to CarbonCure for, in ERA’s words, “innovative technologies that turn carbon dioxide emissions from a waste stream into valuable products right here in Alberta.” The same month, Nixon gave $1.4-million to Lehigh Cement, whose goal is to produce “CO2-neutral” concrete by 2050.
The promise of “green” cement is attracting attention from some of the world’s biggest companies too. BP recently invested US$20-million in Solidia, a US company that says it can reduce the carbon footprint of cement by up to 70 per cent. ERA also gave $3-million to Solidia, which is another partner with Lafarge.
Researchers and engineers across the field are optimistic that achieving carbon-negative concrete is only a matter of time. Another one-time Calgary-based XPRIZE finalist, however, says it’s already there. “We are making cement-free concrete—which means the concrete we produce is actually carbon negative,” Mehrdad Mahoutian, the lead researcher at Carbicrete, told Wired in 2018. “Making a block of concrete typically releases two kilograms of CO2 into the atmosphere …We don’t use cement, saving those two kilos, then inject another kilo of CO2 into the concrete.” Carbicrete, which uses steel slag in lieu of cement, pulled out of the XPRIZE in 2018 after receiving $2.1-million from Sustainable Development Technology Canada to develop a pilot facility in Quebec.
Niven at CarbonCure insists that their concrete ultimately won’t need a public boost. “We don’t want to rely upon regulations or artificial market distortions to drive our growth,” he says. “We want to do it through basic capitalism, meaning we want to make it worthwhile for our producers.” In other words, to make their concrete attractive to construction companies that may not even be seeking to reduce GHG emissions. In this vision, lower emissions will be a bonus of companies having bought stronger, cheaper concrete.
Niven says better government policy would help, though. He points to Hawaii as a forward-thinker: state legislation there requires that reduced-carbon concrete be used by the Department of Transportation if it is equivalent in strength, durability and economics. “That same policy has… been accepted in 1,400 cities across the country through the US Conference of Mayors,” Niven says.
Indeed, the public can play a large role. “Government is a large procurer, if not the largest procurer, of our building materials,” Lafarge’s Moser says. But he says governments can be “hesitant” about new technologies. “There is no technical reason why it can’t be accepted now. It should be written into the procurement protocols that [low-carbon] cement is equivalent to [conventional] cement.”
But even if the new cement were equivalent, Sant, the UCLA professor, says carbon utilization on its own cannot solve our climate problem. “Even if we choose to utilize all of the carbon dioxide in the world,” he says—a logistically complicated endeavour, to say the least—“we’d only be able to use 5 per cent to create… useful materials. We simply emit far too much CO2.” Even the “greenest” concrete could only absorb so much carbon.
The International Panel on Climate Change likewise urges caution in relying too heavily on carbon-negative technology, and writes that carbon mitigation is paramount. Individual experts agree. “You can rule out a silver bullet,” John Shepherd, an author of a European Academies Science Advisory Council report on negative emissions technologies, told The Guardian last year. “Negative-emissions technologies are very interesting but they are not an alternative to deep and rapid emissions reductions.”
The technologies being trialled in Alberta do reduce GHG emissions; they reduce our reliance on emissions-intensive cement; they eliminate other carbon emissions by storing them in concrete. Proponents say they’re essential. “I don’t think we can [continue our rate of growth] without new technologies,” Savilow of Carbon Upcycling says. “It’s not sustainable. We need to change the way we’re viewing and using material.”
Reducing the environmental impact of the world’s favourite building material, Sant agrees, is “overwhelmingly important.” It’s about a revolution in thinking about construction. “Materials have defined our advancement and evolution as a civilization,” Sant says, saying we need to think about less-carbon-intensive concrete as “a new paradigm of materials.”
“The way we do cement today is a process that was invented two centuries ago,” Israel says. “It’s time to reinvent that process… and make this industry compatible with a low-carbon world.”
Sharon J. Riley covers Alberta for The Narwhal. Her work has also been published by Harper’s, The Walrus and Maisonneuve.