Concrete, the ubiquitous building material, is the second-most-used substance on Earth after water. It is also a major contributor to carbon emissions, responsible for about 7.5% of total anthropogenic CO₂ emissions. Researchers from the University of Cambridge have developed a groundbreaking method to produce low-emission concrete at scale, potentially transforming the construction industry’s journey toward net-zero emissions.
The Breakthrough: Recycling Cement in Electric Arc Furnaces
The innovative process, described as "an absolute miracle" by the research team, utilises electric arc furnaces (EAFs) commonly used in steel recycling. This method not only recycles steel but also repurposes used cement, the carbon-intensive component of concrete. Cement is typically produced through a process called clinkering, which involves heating limestone and other materials to high temperatures, releasing significant amounts of CO₂.
In a novel approach, the Cambridge researchers discovered that used cement can effectively replace lime flux in the steel recycling process. Lime flux is traditionally used to remove impurities during steelmaking, resulting in a byproduct known as slag. By substituting lime with used cement, the researchers produced recycled cement that can be used to create new concrete, significantly reducing the need for virgin materials and associated emissions.
Cost-Effective and Scalable Solution
One of the remarkable aspects of this method is that it does not add significant costs to the production of concrete or steel. The Materials Processing Institute, a partner in this project, confirmed that recycled cement could be produced at scale in an EAF, a first in the industry. Moreover, if the EAFs are powered by renewable energy, the process could eventually lead to the production of zero-emission cement.
Professor Julian Allwood from Cambridge’s Department of Engineering, who led the research, highlighted the industry’s initial skepticism towards a world without traditional cement. "We held a series of workshops with the construction industry on how to reduce emissions," Allwood said. "Great ideas emerged, but one thing that was hard to envision was eliminating cement entirely."
The Science Behind the Innovation
Concrete is composed of sand, gravel, water, and cement, which acts as a binder. While cement makes up a small proportion of concrete, it accounts for nearly 90% of the material’s CO₂ emissions. This is because producing cement involves heating limestone to about 1,450°C, a process that releases CO₂ as the limestone decarbonates into lime.
Dr. Cyrille Dunant, the study’s first author, explained how the idea for recycling cement emerged from previous research. The team hypothesised that crushing old concrete to extract sand and stones, then heating the remaining cement could remove water and re-form clinker, the primary component of cement. They tested various slags made from demolition waste in the Materials Processing Institute’s EAF, achieving promising results.
The recycled cement produced contains higher levels of iron oxide compared to conventional cement, but this does not significantly impact performance. The researchers have named this new product "Cambridge Electric Cement."
A Vision for the Future
The Cambridge team envisions scaling up the production of Cambridge Electric Cement, potentially reaching one billion tonnes per year by 2050, about a quarter of current annual cement production. This innovation could play a critical role in reducing the construction industry’s carbon footprint.
However, Allwood emphasises that simply producing lower-emission cement is not enough. "We need to reduce the amount of concrete we use," he said. "Concrete is cheap, strong, and versatile, but we use far too much of it. Reducing usage, without compromising safety, requires political will and regulatory support."
The researchers have filed a patent for their process to aid in commercialising this technology. The project has received support from Innovate UK and the Engineering and Physical Sciences Research Council (EPSRC), part of UK Research and Innovation (UKRI). As this technology progresses, it not only represents a breakthrough for the construction sector but also underscores the vast potential for innovation in achieving a zero-emission future.