There are already cements marketed as “net zero emissions” but this only because someone somewhere plants some trees or in other ways offsets the embedded carbon. But these are reduced carbon cements marketed as zero carbon.  

Cyrille Dunant, Pippa Horton and Julian Allwood say that their Cambridge Electric Cement is something different altogether.

There are many options to make cement with reduced emissions, mainly based on mixing new reactive cement (clinker) with other supplementary materials. However, it had not previously been possible to make the reactive component of cement without emissions. The new invention achieves this for the first time within the parameters of established industrial processes, they say.

The inspiration for Cambridge Electric Cement struck Dr Cyrille Dunant when he noticed that the chemistry of used cement is virtually identical to that of the lime-flux used in conventional steel recycling processes. The new cement is therefore made in a recycling loop that eliminates the emissions of cement production and saves raw materials. It also reduces the emissions required in making lime-flux.

Their process begins with crushing and processing concrete demolition waste to sift out the old cement powder, which is then used instead of lime-flux in steel recycling. As the steel melts, the flux forms a slag that floats on the liquid steel, to protect it from oxygen in the air. After the recycled steel is tapped off, the liquid slag is cooled rapidly in air, and ground up into a powder that is virtually identical to the clinker that is the basis of new Portland cement. Cambridge trials have demonstrated this combined recycling process, and the results show that it has the chemical composition of a clinker made with today’s process.

The new cement was invented as part of the large multi-university UK FIRES programme led by Professor Julian Allwood, which aims to enable a transition to zero emissions based on using today’s technologies differently rather than waiting for the new energy technologies of hydrogen and carbon storage.

Invention of the cement has been rewarded with a research grant of £1.7m from the Engineering & Physical Sciences Research Council, to allow the inventors to collaborate with Zushu Li at Warwick University and Rupert Myers at Imperial College London, to reveal the underlying science behind the new process. The grant will fund an additional team of researchers, to probe the range of concrete wastes that can be processed into Cambridge Electric Cement, evaluate how the process interacts with steel making, and confirm the performance of the resulting material.

Prof Allwood said: “‘If Cambridge Electric Cement lives up to the promise it has shown in early laboratory trials, it could be a turning point in the journey to a safe future climate. Combining steel and cement recycling in a single process powered by renewable electricity, this could secure the supply of the basic materials of construction to support the infrastructure of a zero emissions world and to enable economic development where it is most needed.”

The Cambridge breakthrough has generated a degree of excitement on the LinkedIn social media platform. However, several commentators question the veracity of the net zero claim, given that the product requires an existing (carbon-intensive) building to be knocked down and crushed by heavy machinery, and for steel to be melted.

“The only net zero building remains the one that is not built,” said Olivier Elamine, chief executive of German property firm Alstria.

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