When you manufacture cement, you heat up limestone and other clay-like materials to an astounding 2,552 degrees Fahrenheit (1,400 Celsius). Creating temperatures that high requires an awful lot of energy and (usually) a large amount of fossil fuels. Not only that, but when you heat up limestone — a carbonate — it breaks down into calcium oxide and carbon dioxide (CO2). This double whammy of incredibly high energy needs, plus the use of a feedstock that directly releases CO2, means cement manufacturing is one of the most carbon-intensive industries on the planet.
In fact, according to a 2018 report by Chatham House, this one industry contributes around 8% of all global carbon dioxide emissions. For comparison, that's roughly half of the entire transportation sector's CO2 output. Or, as Bloomberg News recently put it, cement is responsible for more CO2 emissions than all the trucks in the world.
An overlooked contributor to the problem
By now, most of us who follow the issue of global climate change know we should probably drive our cars less, eat less meat and reduce our energy consumption. But for some reason there's less recognition of the fact that one of the basic building blocks (hah!) of the modern built environment is directly contributing to our planetary crisis on an almost unimaginable scale. That may be changing, however.
As Barbara Grady at Business Green reported in 2016, many cement makers are planning for a day when carbon pollution no longer gets a free pass, and they're exploring both incremental improvements to their manufacturing methods as well as more radical reconsiderations of how cement is made and what it's made from.
In 2018, the London-based Global Cement and Concrete Association (GCCA), which represents about 30% of worldwide cement-production capacity, announced the industry's first sustainability guidelines, according to Yale Environment 360. The guidelines provide a framework for GCCA members to monitor and report on things like emission levels or water management, and the GCCA will also verify and report the data from its members. And in April 2019, the GCCA formally joined forces with the Concrete Sustainability Council, which certifies the sustainability of concrete plants and their supply chain around the world.
Some companies are tweaking their recipes in search of climate-friendlier cement, Bloomberg explains, while others are exploring substitute materials. These include fly ash from coal plants, slag from steel mills or pozzolan, reportedly a popular option in Brazil. Some companies are going even further, trying to turn the entire process of cement production not just carbon-neutral but carbon-negative.
Turning cement emissions into liquid fuel
One of the initiatives Grady profiled is HeidelbergCement's partnership with a company called Joule Technologies. Together, the two firms are working on a process that captures CO2 emissions from cement manufacturing smokestacks and, using engineered bacteria as a catalyst, transforms those emissions into a feedstock for liquid fuel. Because that liquid fuel can be used to replace fossil fuel-based transportation fuels, the end result is significantly more "bang" for your CO2 buck. If all goes to plan, Heidelberg and Joule have projected commercial applications of their technology within five years.
Cement as carbon sequestration
Another company profiled by Grady is Solidia, a U.S.-based firm that has developed a method for injecting CO2 captured from industrial operations into cement during the manufacturing process. That CO2 then acts as a binding agent, becoming permanently stored within the cement itself. This creates what the company claims could be the world's first carbon-negative cement, meaning it sequesters more carbon than was produced during manufacturing.
A long way to go
But let's not get too carried away about the potential for carbon negativity. Leading environmental thinker and author Tim Flannery, in his 2015 book "Atmosphere of Hope," covered the idea of carbon-negative cement as part of his exploration of "third way" technologies — approaches that could help us draw down some of the carbon that has already accumulated in the atmosphere. For cement to sequester even one gigaton of carbon per year, says Flannery, 80% of the world's cement manufacturing would have to switch over to technologies like Solidia's. Meanwhile, the combined academies of the United States have estimated we'd need to sequester or otherwise draw down a whopping 18 gigatons of CO2 to start reducing atmospheric concentrations by even one part per million.
According to the Chatham House report, the cement industry's annual CO2 emissions would need to fall by at least 16% to bring it in line with the Paris Agreement. On a "business as usual" trajectory, the report added, global cement production is set to increase to over 5 billion metric tons per year over the next 30 years.
Editor's note: This article has been updated with new information since it was originally published in January 2016.