New cement recycling process could slash emissions

In a groundbreaking development, researchers at the University of Cambridge have unveiled a revolutionary process that could significantly reduce the environmental impact of the construction industry. By recycling cement using the same furnaces employed in steel recycling, the new method has the potential to eliminate emissions from cement production entirely.

Professor Julian Allwood, who led the research at Cambridge's Department of Engineering, commented on the significance of this innovation: "The industry uses a third of all the emissions in the world. And half of those come from just two materials: steel and cement. We use half a tonne of cement every year for every person alive on the planet."

Conventional cement production involves heating limestone and other raw materials to about 1,450°C in large kilns, a process that releases large amounts of CO2 as the limestone decarbonates into lime. While the industry has made efforts to reduce emissions by blending cement with alternative materials like fly ash from waste incineration, these substitutes are limited in supply and still require cement for activation.

The Cambridge Electric Cement (CEC) process overcomes these limitations by directly recycling cement from demolished concrete. The old concrete is crushed to a higher degree than usual to separate the cement paste from the sand and aggregates. This recovered cement paste contains the necessary oxides and calcium to be "re-clinkered" without the need for virgin limestone.

The recycled cement paste is then used as a flux in electric arc furnaces (EAFs) during steel recycling. The high temperatures in the EAF cause the old cement to be reformed into clinker as it mixes with the molten slag floating on the steel. When cooled rapidly, this slag forms cement clinker with the same mineral composition as conventional Portland cement.

"We have developed what we think will be the world's first process for making zero emissions cement," explained Allwood. "What we've shown already is that we can recycle cement by processing it through the same furnace where we recycled steel. And we know that if in the future that furnace is powered by electricity that has no emissions, our process could make cement with no emissions whatsoever."

The CEC process integrates cement recycling into steel production, reducing emissions from both industries without adding significant costs. The researchers estimate that by implementing this technique at scale, the UK could meet about a third of its cement needs within a decade. Globally, the process has the potential to slash cement emissions by 80 per cent compared to business-as-usual scenarios by 2050.

The success of the CEC process hinges on the efficient recovery of cement paste from demolition waste. While technologies for this purpose exist, they are not yet widely deployed. The researchers emphasise that the development of concrete recycling infrastructure will be crucial to realising the full potential of this innovation.

The team is now working with the Materials Processing Institute to scale up the process, with industrial-scale trials expected to produce around 60 tonnes of recycled cement clinker over a two-hour period. The recycled cement contains slightly higher levels of iron oxide than conventional cement, but the researchers say this has minimal impact on its performance and durability.

The research team has filed a patent for the CEC process and is setting up a company to commercialise the technology. With the right support and investment, this groundbreaking innovation could be scaled up rapidly, providing a viable path to zero-emission cement production on a global scale.

Allwood added: "We're really excited about this innovation, I think potentially is one of the biggest material breakthroughs that have come out of Cambridge in the last few decades. [...] Before we started, there was literally no option on the table for making cement with no emissions."