Climate Insider Brief:

• Researchers at the University of Cambridge have developed a method to produce low-emission concrete by using electric arc furnaces (EAFs) in steel recycling to recycle cement, reducing the carbon footprint of both steel and concrete production.
• Concrete production is a major source of CO₂ emissions, responsible for 7.5% of global emissions. The new method substitutes used cement for lime flux in steel recycling, producing recycled cement and reducing emissions without significantly increasing production costs.
• The Cambridge Electric Cement process is projected to scale up to produce one billion tonnes of recycled cement per year by 2050. 

Researchers from the University of Cambridge have developed a method to produce very low emission concrete at scale, marking a significant step towards achieving net zero emissions. This method leverages electrically-powered arc furnaces used in steel recycling to simultaneously recycle cement, the carbon-intensive component of concrete.

Concrete is the second-most-used material globally, after water, and is responsible for approximately 7.5% of total anthropogenic CO₂ emissions. Finding a scalable, cost-effective way to reduce concrete emissions while meeting global demand is a major challenge in decarbonization efforts.

The Cambridge team discovered that used cement can substitute for lime flux in steel recycling. Lime flux, used to remove impurities, typically ends up as waste (slag). By replacing lime with used cement, the process yields recycled cement for new concrete production.

The method, detailed in the journal Nature, does not significantly add to the costs of concrete or steel production. It reduces emissions from both sectors due to the decreased need for lime flux. Tests conducted by the Materials Processing Institute, a project partner, confirmed that recycled cement could be produced at scale in an electric arc furnace (EAF). This achievement paves the way for potentially zero-emission cement if the EAF is powered by renewable energy.

Professor Julian Allwood from Cambridge’s Department of Engineering, who led the research, noted the necessity of cement in construction, stating, “One thing they couldn’t or wouldn’t consider was a world without cement.”

Concrete is composed of sand, gravel, water, and cement. Although cement is a small proportion of concrete, it accounts for almost 90% of concrete emissions. Cement production involves clinkering, a process where limestone and other raw materials are heated to about 1,450°C in large kilns, releasing significant CO₂ as limestone decarbonates into lime.

While scientists have explored substitutes for cement over the past decade, they found that roughly half of the cement in concrete can be replaced with alternatives like fly ash. However, these alternatives require chemical activation by the remaining cement to harden, and their supply is insufficient to meet the global demand of roughly four billion tonnes per year.

Dr. Cyrille Dunant, the study’s first author, explained the concept: “If it were possible to crush old concrete, taking out the sand and stones, heating the cement would remove the water, and then it would form clinker again.” The researchers used a bath of liquid metal in an electric arc furnace to facilitate this chemical reaction.

The team tested various slags made from demolition waste, adding lime, alumina, and silica, and processed them in the Materials Processing Institute’s EAF. They found that the combination of cement clinker and iron oxide forms an excellent steelmaking slag, which, when cooled quickly, reactivates the cement without adding cost to the steelmaking process.

The resulting recycled cement contains higher levels of iron oxide than conventional cement but performs similarly. The Cambridge Electric Cement process is scaling rapidly, with projections to produce one billion tonnes per year by 2050, representing about a quarter of current annual cement production.

Professor Allwood emphasised the dual necessity of producing zero emissions cement and reducing cement and concrete usage overall. “Concrete is cheap, strong and can be made almost anywhere, but we just use far too much of it,” he said, advocating for political will to reduce consumption without compromising safety.

The researchers have filed a patent to commercialise the process, supported by Innovate UK and the Engineering and Physical Sciences Research Council (EPSRC), part of UK Research and Innovation (UKRI). This innovation highlights the broader opportunities for decarbonization beyond the energy sector, potentially transforming the construction industry.

SOURCE: EurekAlert

Featured Image: Credit: Materials Processing Institute, UK.