One of the world’s biggest industries—and a leading producer of greenhouse gas emissions—may finally be making moves to combat climate change.
The World Cement Association recently held its first-ever global climate change forum, where industry leaders and scientists discussed strategies to reduce the industry’s carbon footprint. It will help inform the development of a climate action plan, which the WCA intends to release in September, aimed at outlining pathways for low-carbon cement production.
“The Global Climate Change Forum made clear the importance of stimulating innovation if we are to have any hope of achieving the Paris climate goals,” Bernard Mathieu, director of the WCA’s climate change program, said in a statement.
While industries of all kinds are exploring ways to reduce their carbon footprints, the cement industry—unglamorous as it may sound—is among the most significant to join the discussion.
Cement is the most widely used man-made material in existence—it forms concrete when mixed with water, and is used in the construction of everything from buildings and bridges to roads and sidewalks and all kinds of other infrastructure.
But while cement has largely shaped the modern built environment, it’s also a massive source of carbon dioxide to the atmosphere. It single-handedly accounts for about 7 percent of all global carbon emissions, according to estimates from the International Energy Agency. That makes it the second-largest single industrial emitter in the world, second only to the iron and steel industry.
It’s a problem that often receives little attention among the public. But concern among scientists is rising. As global population grows, some estimates suggest cement production could increase by as much as 23 percent by 2050. And some experts suggest that unless the industry substantially reduces its emissions, it could put the Paris Agreement’s global climate targets in jeopardy.
An April report from IEA and the industry-led Cement Sustainability Initiative notes that the industry, in its current form, is inconsistent with trajectories that would allow the world to meet a 2-degree Celsius temperature target. Reaching this goal, the report suggests, “implies significantly greater efforts to reduce emissions from cement makers.”
THE RACE FOR SOLUTIONS
Portland cement—the most widely used type of cement around the world, and the product specified in many modern construction codes—was patented nearly 200 years ago and has become an essential component of the built environment. In the years since, little has changed about the production process, according to Gaurav Sant, a professor of civil and environmental engineering at UCLA.
“There have been improvements in process efficiencies, but broadly speaking it’s not that different,” he told E&E News.
That’s a big problem for the climate, because the process releases large amounts of carbon dioxide. The industry’s huge carbon footprint partly stems from its high fuel requirements, which are mostly satisfied by fossil fuels. But more than half of its emissions—and perhaps as much as two-thirds, by some estimates—actually come from the chemical production process itself, which releases large amounts of carbon dioxide as a byproduct.
Portland cement is produced in large part with limestone, a type of rock that’s composed mainly of a chemical compound called calcium carbonate. To produce the sticky, binding cement, the limestone must be heated at high temperatures—around 1,500 C, according to civil and environmental engineering expert Claire White of Princeton University.
The intense heating process in and of itself, she noted, requires a massive amount of fuel. But it also causes the limestone to chemically decompose, leaving behind a compound called calcium oxide, which is used in the final cement product, releasing carbon dioxide gas into the atmosphere.
The specific formula used for cement, and the fact that it’s remained unchanged for so long, makes the industry an unusually challenging one when it comes to climate action. A commentary published last month in Science evaluated a variety of “difficult-to-decarbonize” services and processes. Tackling cement, it noted, doesn’t have a single solution—it will require a variety of approaches, including major changes in both the materials used and the manufacturing process itself.
The problem has drawn the attention of major international organizations in recent years, some of which are now advising the industry on ways to cut carbon. IEA’s April report contained a low-carbon technology road map, aimed at reducing cement industry emissions 24 percent by 2050. The report outlines a variety of strategies that could help achieve that goal—everything from alternative fuels to carbon capture technology to new chemical recipes for the cement product itself.
Research groups around the world are already tackling many of these issues. Some groups are working on chemical formulas that would reduce the amount of “clinker”—the substance that requires the heating of limestone—that goes into the cement.
White, the Princeton engineer, leads the university’s Sustainable Cements Group, which is working on ways to eliminate the need for clinker altogether. It’s possible to make cement-like products using other substances instead, she noted, including recycled byproducts from other industries, such as steel slag, fly ash from coal-fired facilities or certain types of clays. Treating these substances with special chemical compounds known as alkalis “can make the powders reactive,” White said, “and we can form similar building blocks at the molecular level compared to what’s in portland cement concrete.”
That said, there’s some debate about exactly how much carbon output is associated with alkali-activated cements, she added, which can sometimes make it difficult to compare with portland cement. It partly depends on exactly what type of alkali sources, and how much, are used in the process, and how far the materials must be shipped. Some estimates suggest the practice has the potential to lower emissions by as much as 40 to 80 percent compared with portland cement, White said.
Other researchers are focusing on different tactics. Sant, the UCLA engineer, is involved with a research team developing a product they’ve dubbed “CO2NCRETE.” The process relies on “carbon upcycling”—using CO2 emissions captured from industrial activities to produce a cement-like, and potentially carbon-neutral, building material. The CO2NCRETE process is unique, Sant says, because it can utilize the captured carbon emissions as is, without the need for extra processing.
Other experts have pointed out that concrete naturally absorbs carbon dioxide. It’s a slow process, but over the course of decades, it may be able to soak up a substantial amount of the emissions it put into the atmosphere in the first place via the limestone heating process.
A 2016 paper in Nature Geoscience suggested that the world’s concrete has been absorbing about 43 percent of those original emissions. There may be some ways to speed up or strengthen this absorption process, Sant noted—it’s an area his own research group is focusing on.
Steven Davis, an earth system scientist at the University of California, Irvine—one of the authors of the Nature Geoscience paper, as well as last week’s Science commentary—noted that concrete’s absorption potential implies that there may be ways to make cement production carbon negative.
If cement production facilities were all outfitted with carbon capture and storage technology, for instance, then a substantial amount of the emissions produced on-site could be stopped from entering the atmosphere. Later, the concrete produced would soak up even more carbon dioxide, which could eventually amount to a “net drawdown from the atmosphere,” he told E&E News.
While different research groups are focusing on different approaches, IEA’s technology road map suggests that reducing emissions quickly enough to help meet global climate goals will require a variety of strategies all working together. This is likely to be the most successful approach, according to White.
“There might be front-runners in terms of what can help or what we can use in the near future, but that doesn’t mean we shouldn’t be looking at more innovative materials down the line,” she said. “It’s not just one technology that we need to look at to combat the sustainability issues associated with the concrete industry.”