Concrete, the most used material in the world after water, is responsible for 8% of global CO2 emissions. Most of such emissions come from the cement needed to give concrete its strength. At the same time, the UK's concrete industry extracts 180Mt/year of natural aggregates (sand/gravel) from our quarries and riverbeds, with huge negative environmental impact. The UK also produces 45Mt/year of 'waste' concrete from old, demolished buildings. Concrete absorbs CO2 through a chemical process called 'carbonation', which increases its strength. Concrete carbonation rarely happens naturally as it needs specific temperature, relative humidity, and can take 100+ years to occur. End-of-life concrete has huge potential to absorb significant amounts of CO2 and to be replace natural aggregates to produce new concretes. However, end-of-life concrete from demolition is very porous, and thus the strength of the new concrete is always below standards. Therefore the UK's concrete/construction industry downcycles end-of-life concrete in backfill/drainage applications.

This project aims to develop new CO2-absorbing aggregates made of crushed upcycled end-of-life concrete from demolished buildings. We have an innovative technology that sequesters CO2 into end-of-life concrete (30% btw) and reduces carbonation time to around 100 hours, instead of years. By speeding up carbonation, we can a) reduce the porosity of end-of-life concrete from demolition, b) increase the strength and durability of new concrete, and c) replace natural aggregates with crushed end-of-life concrete in the production of new concrete for structural applications. Valorising the properties of end-of-life concrete and sequestering CO2 into it allows our technology to be economically viable at large scale. Our approach recycles end-of-life concrete and injects CO2 into it, making concrete a very low-emission material.

The UK is committed to large infrastructure projects (HS2, Sizewell C, thus huge demand for concrete) and to reach net-zero by 2050\. The concrete/construction industry urgently needs to adopt circular economy and CO2-capture technologies to deliver such commitments. The results of this project will help the UK move faster to a net-zero circular economy by reusing, reducing and upcycling end-of-life concrete.