Could we turn rubble into circular cement?

The innovative process uses existing steel-making infrastructure

Spotted: Concrete is a staple of the modern built environment, with the UK producing 21 million metric tonnes of the ready-mixed material in 2022 alone. But our mass production of concrete comes at a huge carbon cost, mainly due to one key component: cement. Cambridge Electric Cement (CEC) may have a solution that could change this, however.

The Cambridge University spinout has found a way to transform old concrete from demolition sites into a circular cement, using electric arc furnaces that currently process recycled steel. The final product acts as a direct replacement for Portland cement in new mixtures.

First, the company crushes the concrete to retrieve the old cement powder, which is used instead of lime-flux within the furnace. This flux forms a slag, which floats on top of the steel as it melts. The liquid steel is tapped off and once the slag meets the air and cools, it solidifies and is ground up into a powder to create an identical replacement for Portland clinker. Then, the clinker can be blended into cement and used in new construction projects.

Traditional cement production is so carbon-intensive because the kilns it relies on require extremely high temperatures, typically reached through the use of fossil fuels. Plus, the calcination process, where calcium carbonate is converted into lime (the key component of cement), releases CO2 as a by-product. CEC’s cement-making process avoids both of these, all while making use of existing steel production infrastructure, allowing construction teams to quickly cut the carbon cost of their building materials.

Written By: Matilda Cox