The magic of recycling cement
In an exciting breakthrough, researchers from the University of Cambridge have unveiled a method to produce very low-emission concrete on a large scale. This innovation has the potential to revolutionise the transition to net zero emissions.
Described as "an absolute miracle" by the researchers, the method leverages electrically-powered arc furnaces, traditionally used in steel recycling, to recycle cement, the most carbon-intensive component of concrete.
Given that concrete is the second most-used material on Earth, after water, and is responsible for around 7.5% of global CO₂ emissions, this development could be a game-changer in reducing our carbon footprint.
How it works
The key to this method lies in repurposing used cement as a substitute for lime flux, which is used in steel recycling to eliminate impurities and typically becomes waste. By replacing lime with used cement, the by-product is recycled cement that can be used to create new concrete.
Published in the journal Nature, the research indicates that this recycling method does not significantly increase costs for concrete or steel production. Moreover, it substantially lowers emissions from both industries by reducing the need for lime flux.
Scalable and sustainable
The Materials Processing Institute, a partner in this project, conducted recent tests that demonstrated recycled cement could be produced at scale in an electric arc furnace (EAF). This marks the first time such a feat has been achieved. Looking forward, if the EAF is powered by renewable energy, this method could eventually yield zero-emission cement.
A future without cement?
Professor Julian Allwood from Cambridge’s Department of Engineering who led the research, explained, “We held a series of workshops with members of the construction industry on how we could reduce emissions from the sector. Lots of great ideas came out of those discussions, but one thing they couldn’t or wouldn’t consider was a world without cement.”
Concrete, composed of sand, gravel, water, and cement, relies heavily on the latter as a binder. Despite being a small component, cement accounts for nearly 90% of concrete emissions. Cement production involves heating limestone and other materials to about 1,450°C, releasing large amounts of CO₂ as the limestone decarbonates into lime.
Innovative solutions
While substitutes for cement, such as fly ash, have been explored over the past decade, these alternatives must be chemically activated by remaining cement to harden. Moreover, the global demand for cement, which is roughly four billion tonnes per year, far exceeds the availability of these substitutes.
Professor Allwood remarked, “It’s also a question of volume – we don’t physically have enough of these alternatives to keep up with global cement demand. We’ve already identified the low-hanging fruit that helps us use less cement by careful mixing and blending, but to get all the way to zero emissions, we need to start thinking outside the box.”
Taking a visionary approach
Dr. Cyrille Dunant, the first author of the study, had a visionary idea: by crushing old concrete, extracting the sand and stones, and heating the cement, it could form clinker again. An electric arc furnace, used for steel recycling, seemed a promising tool for this chemical reaction.
The research team tested various slags made from demolition waste, adding lime, alumina, and silica, and processed them in the Materials Processing Institute’s EAF with molten steel. Rapid cooling resulted in reactivated cement without adding extra costs to the steelmaking process.
Looking ahead
The Cambridge Electric Cement process has been scaling rapidly, with projections to produce one billion tonnes per year by 2050 – roughly a quarter of current annual cement production. While producing zero emissions cement is an extraordinary achievement, Professor Allwood emphasised the need to reduce overall cement and concrete usage.
“Concrete is cheap, strong, and can be made almost anywhere, but we just use far too much of it,” he said. “We could dramatically reduce the amount of concrete we use without any reduction in safety, but there needs to be political will to make that happen."
Beyond the construction industry, the researchers hope that Cambridge Electric Cement will serve as a beacon, highlighting that innovation opportunities on the path to zero emissions extend far beyond the energy sector.
Carl Dodd, Property Revolutions Ltd.
