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

Lead Research Organisation: University of Cambridge
Department Name: Engineering

Abstract

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.

Publications

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Description Presentation at the Concrete Centre event 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Industry/Business
Results and Impact A presentation given by Dr Cyrille Dunant as part of this event:
Reduce and reuse are priorities good Circular Economy practice and there are a growing number of examples of new developments benefiting from the reuse of an existing concrete frame. But what is best practice when concrete is eventually demolished?
Recent data indicates that in the UK 97.5% of all concrete construction and demolition waste is recycled, used primarily as unbound sub-base for roads and buildings. But is this the best use of this secondary resource? What other opportunities exist or are in development? Research undertaken at the university of Cambridge, has established that cement paste recovered from construction demolition waste can be used in the manufacture of a new cementitious material Cambridge Electric Cement. Other potential uses include carbon capture use and storage, the manufacture of new concrete as recycled aggregate or recycled concrete paste as a cement replacement.
This joint event between Cambridge University and MPA The Concrete Centre, brings together a broad community of representatives from industry to explore the opportunities, challenges, and potential for alternative uses of concrete demolition waste. It will include an explanation of some of the new uses that are being developed and their potential production and separation processes, as well as examples of live projects in progress.
Year(s) Of Engagement Activity 2023
URL https://www.concretecentre.com/CPD-Events/Events/Making-better-use-of-recycled-concrete-S1.aspx
 
Description Steel & Cement Circularity | EAF Transformation a UK research collaboration by Patricio Burdiles 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Industry/Business
Results and Impact Patricio Burdiles (senior project manager) gave a presentation to the audience at the ESTEP Barcelona conference.
Year(s) Of Engagement Activity 2023
URL https://www.estep.eu/assets/Uploads/4-Burdiles-Eoin-Cambridge-Celsa-cement2zero-ESTEP.pdf