Scientists have discovered a method to recycle cement from demolished concrete buildings, which could significantly reduce carbon emissions associated with cement production.

Cement, the world’s most common construction material, contributes substantially to greenhouse gas emissions due to the chemical reactions involved in its production.

Typically, cement is made by heating limestone to extremely high temperatures, a process that requires burning fossil fuels and releases large amounts of carbon dioxide (CO2).

Recycling cement could drastically lower its carbon footprint. Researchers suggest that using electric-powered furnaces with renewable energy sources like wind and solar could potentially eliminate CO2 emissions altogether.

This innovation is crucial since cement is foundational to modern infrastructure. It binds sand and aggregate in concrete, the second most widely used material on Earth after water.

However, cement production is a major climate change driver. If considered a country, cement would rank as the third-largest emitter of CO2, following China and the United States, accounting for 7.5% of human-made emissions.

The polluting nature of cement lies in its production process, where limestone is heated to about 1600°C in kilns powered by fossil fuels. This not only generates CO2 from burning the fuels but also releases CO2 from the limestone itself. Combined, these processes emit approximately one tonne of CO2 per tonne of cement produced.

A research team from Cambridge University has developed a way to mitigate these emissions by reactivating used cement through exposure to high temperatures. This process is well-understood and has been performed at scale in cement kilns. The breakthrough came when the team realised they could use the heat generated from another industry—steel recycling.

In steel recycling, chemicals known as slag float on the molten metal to prevent impurities. The Cambridge team discovered that used cement has a similar composition to slag used in electric arc furnaces. They tested the process at a small-scale electric arc furnace at the Materials Processing Institute in Middlesbrough and successfully produced high-grade “Portland” cement, calling it “electric cement.”

Lead scientist Cyrille Dunant claimed that this method could enable zero-carbon cement production.

“We have shown the high temperatures in the furnace reactivate the old cement and because electric arc furnaces use electricity they can be powered by renewable power, so the entire cement making process is decarbonised.,” he said.

Additionally, it could make steel recycling less polluting by reducing the carbon cost of making slag chemicals.

Mark Miodownik, Professor of Materials and Society at University College London, praised the innovation as “genius” and believes it could lead to significant emissions reductions if scaled profitably.

“Can it compete against the existing infrastructure that is very unsustainably going to keep pumping cement into our lives”, he asks.

“Cement is already a billion-dollar industry. It’s David and Goliath we are talking about here.”

Electric cement could also be cheaper to produce, leveraging waste heat from the steel recycling process.

The Spanish company Celsa plans to replicate this process in its full-scale electric arc furnace in Cardiff.

The Cambridge team estimates that their low-carbon cement could meet up to a quarter of the UK’s demand, given current steel recycling rates. As the use of electric arc furnaces increases, the production of electric cement could rise accordingly, offering a scalable solution to reduce global cement emissions dramatically.

 

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