Concrete and steel production are major contributors to CO2 emissions, but researchers from Cambridge University have developed a revolutionary solution that could recycle both materials simultaneously. By introducing old concrete into steel-processing furnaces, the process not only purifies iron but also produces “reactivated cement” as a byproduct. When powered by renewable energy, this method could potentially yield carbon-zero cement.

Scientists have long sought to make concrete more environmentally friendly. Efforts include altering the concrete mix to replace the most polluting ingredients, such as limestone, or designing concrete to absorb more CO2 from the atmosphere after being laid. In their new study, Cambridge researchers explored how waste concrete could be transformed back into clinker—the dry component of cement—ready for reuse.

“I had a vague idea from previous work that 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,” explained Dr. Cyrille Dunant, the study’s lead author. “A bath of liquid metal would help this chemical reaction along, and an electric arc furnace, used to recycle steel, felt like a strong possibility. We had to try.”

An electric arc furnace requires a “flux” material, typically lime, to purify steel. This molten substance captures impurities, rises to the surface, and forms a protective layer that prevents the new pure steel from oxidizing. Normally, the used flux is discarded as waste.

In the Cambridge method, the lime flux is replaced with recycled cement paste. Remarkably, this substitution not only purifies the steel effectively but also results in new Portland cement when the leftover slag is rapidly cooled in air. The resulting concrete performs similarly to the original material.

Crucially, this technique does not significantly increase the costs of concrete or steel production and significantly reduces CO2 emissions compared to traditional methods. If powered by renewable energy, the process could potentially produce zero-emission cement. The technique has already been trialed in furnaces producing a few dozen kilograms of cement, and industrial-scale trials are underway this month, aiming to produce about 66 tons of cement in two hours. Researchers estimate that this process could scale up to produce one billion tonnes of “electric cement” by 2050.

“Producing zero emissions cement is an absolute miracle, but we’ve also got to reduce the amount of cement and concrete we use,” said Professor Julian Allwood, who led the research. “Concrete is cheap, strong, and can be made almost anywhere, but we just use far too much of it. 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.

“As well as being a breakthrough for the construction industry, we hope that Cambridge Electric Cement will also be a flag to help the government recognize that the opportunities for innovation on our journey to zero emissions extend far beyond the energy sector.”

A patent has been filed for the process, marking the first step towards commercialization. The research was published in the journal Nature, and the team describes their work in an accompanying video.

This innovative approach not only addresses significant environmental concerns but also paves the way for a more sustainable construction industry, contributing to the global efforts to reduce carbon emissions.

By Impact Lab