The World’s Most-Used Material Has a Massive Carbon Problem. A Bolt of Plasma May Fix It

Cement, the key binding ingredient in concrete, is the most consumed manufactured material on Earth. It’s unmatched in its affordability, durability, versatility, and-unfortunately-its carbon footprint. Cement production releases more than a billion tons of carbon dioxide per year, accounting for about 8% of global emissions. Now, a team of researchers may have figured out how to slash those emissions significantly. The vast majority of the cement industry’s carbon emissions stem from the heating process that turns a mix of limestone, clay, and other ingredients into “clinkers,” rocky solids that are then ground into cement powder. The raw materials are heated inside fossil fuel-powered kilns that reach temperatures as high as 2,552 degrees Fahrenheit (1,400 degrees Celsius), making the process very carbon intensive. For every ton of clinkers produced, about one ton of CO2 is emitted. The new approach was presented by Qi Zheng, a postdoctoral researcher at Stanford University, at the fall meeting of the American Chemical Society on August 25. It eliminates the need for fossil fuel-powered kilns through plasma heating, which involves directing electricity through ionized gas. If that electricity comes from clean power sources, the researchers say the entire plasma heating process could be emission-free. “We are motivated by solving real-world problems, and decarbonizing cement production is one of the most difficult challenges facing heavy industry,” Zheng told Gizmodo in an email. “Cement is essential to modern infrastructure, so our goal is not simply to replace it but to find a practical way to manufacture it with substantially lower carbon emissions while maintaining the performance and scalability that the industry requires.” A concrete solution In proof-of-concept tests, plasma heating generated temperatures above 4,352 degrees F (2,400 C), allowing the raw materials to fuse into clinkers nearly 100 times faster than with traditional heating, according to the researchers. By shortening the amount of time required for heating, the new method also reduced waste heat, boosting thermal efficiency from roughly 30% to 80%. “Instead of relying on a conventional rotary kiln and transferring heat from combustion gases through multiple intermediate steps, our approach delivers extremely intense heat directly to the material,” Zheng said. “This direct heating is also what enables the very rapid processing demonstrated in our study.” When he and his colleagues looked at their “low-carbon” cement under an electron microscope, they saw that plasma heating had created some nanoscale defects. That may sound like a bad thing, but these imperfections dissolved quickly in water and actually improved the cement’s ability to set, making it stronger than traditional cement. The researchers also found that their plasma heating method worked when using cement waste obtained from recycling facilities as the raw material. However, cement waste can vary depending on where and when it is collected, so Zheng and his colleagues will need to test “whether the new technology is robust enough to deal with all kinds of waste, or if we need to screen a little bit before we feed the material into the machinery,” he said in a statement. It would also take an enormous amount of scaling to implement this plasma heating methodology across the cement industry and meet global demand, so it’s not likely fossil fuel kilns anytime soon. “We recognize that laboratory success is only the first step,” Zheng said. “Further validation at much larger scale-from tons to ultimately kilotons of production-will be essential before the technology can be considered ready for widespread industrial adoption.” The next step is to collaborate with cement industry stakeholders to test and scale their method for mass production. The race to net-zero Despite the long road ahead, this breakthrough marks an important step toward decarbonizing cement production, and there is an urgent need to do so. The industry has set a goal of reaching net-zero emissions by 2050, and to stay on track, it needs to achieve a 40% reduction from 2020 levels by 2030. Previous studies have shown that concrete passively absorbs carbon dioxide and therefore offsets some of the emissions from cement production, but a recent study published in Nature’s Communications Sustainability suggests the offset is negligible. “Ambient carbonation cannot be relied upon as a meaningful tool for reducing atmospheric carbon dioxide accumulations,” lead author Gaurav Sant, a professor of civil and environmental engineering at the University of California, Los Angeles, said in a statement. “The effect is real and substantial when viewed in isolation, but it’s trivial at the gigatonne scale that matters-and it is far too slow to help the cement industry meet its 2030 goal of cutting carbon emissions by 40%.” Switching to low-carbon production methods could actually make a difference. The world will never stop needing more cement, but advancements like this plasma heating technology show that it may not have to come at such high cost to the climate.