Cambridge Electric Cement: Zero-emissions cement from old concrete paste replacing flux in electric-arc furnaces

As the world moves towards zero emissions, decarbonising cement is often described as the most difficult challenge. Portland Cement, which is used to make concrete and mortar, is made in tremendous volumes (more than 500 kg per person per year for everyone on the planet), is cheap (~£60/tonne) and has excellent properties for construction. However, it causes a quarter of all the world's industrial emissions, both due to fuel combustion in high-temperature cement kilns, and because the chemistry of converting limestone into clinker, the key ingredient of cement, inevitably causes the release of carbon dioxide. Many alternative compositions of cement are under development, but although some may lead to reduced emissions, none have zero emissions. Two possible approaches to capturing and storing emissions are under development - one capturing all the emissions of a plant and storing them underground, and the other embedding emissions within pre-cast blocks - but neither is yet operating at scale, and both face many challenges.

Without cement, we will have no concrete, and construction will have to change radically largely shifting from new-build to retrofit and adaption. Countries responsible for around 70% of the world's GDP have now committed to zero emissions targets by 2050 or 2060, so the problem of cement emissions is both large and urgent.

This proposal explores the world's first process that could produce Portland cement with no emissions. The investigators noticed that the lime-flux used in today's electric steel-recycling furnaces has almost the same chemical composition as that of old cement paste - the material that is left when old concrete is crushed, and sand and aggregate is removed. In preliminary trials, using the small electric arc furnace of the Material Processing Institute, we replaced the conventional flux with used cement. We separated the hot liquid slag that floats on the surface of molten steel during recycling and cooled it to form a powder which we then mixed with gypsum and cast into small cement samples. Analysis of our tiny pilot study cement samples showed that they were very similar to conventional Portland cement. This points to the exciting possibility that we could make cement as a by-product of steel recycling, which could be powered by non-emitting electricity - therefore giving us both zero emissions steel and zero emissions cement.

This proposal aims to explore the science around this discovery. We need to find out how the composition of old cement varies, and how this variation affects our new product. We need to explore what effect our new process has on conventional steel recycling - does it change the composition of the steel, does it damage the furnace lining, and how does the type of steel being recycled affect our new cement? And we need to find out more about the properties of our new cement: how durable is it, how quickly does it reach full strength, and so on.

If this new process is as good as we hope, we will want to develop it rapidly to commercial scale, and the technique for making it could become a major UK export. The final component of our proposal is therefore to develop a "roadmap" for taking the idea from lab-scale trials to full deployment. We will explore this question with a consortium of partners, a science advisory panel, and with outward facing partners who could help us champion the new approach.