Climate change: UK breakthrough could reduce CO2 emissions from cement

Scientists say they have found a way to recycle cement from demolished concrete buildings.

Cement is the most common building material in the world, but it is also a huge source of planet-warming gas emissions.

This is due to the chemical reactions when you heat limestone to high temperatures by burning fossil fuels.

Recycling cement would greatly reduce the carbon footprint. Researchers say that if they switched to electric-powered ovens and used renewable energy such as wind and solar energy instead of fossil fuels, it could mean no greenhouse gases are released at all.

And that would be a big problem. Cement is the foundation of the modern economy, both literally and figuratively.

It is what binds the sand and aggregate together in concrete, and concrete is the most used material in the world after water.

It is also a major driver of climate change. If cement were a country, it would be the third largest source of emissions after China and the US, responsible for 7.5% of man-made CO2.

The problem is the unique contaminant chemistry of the material.

It is made by heating limestone to 1600 degrees Celsius in giant furnaces powered by fossil fuels.

These emissions are just the beginning. The heat is used to drive carbon dioxide out of the limestone, leaving a cement residue.

Add both sources of pollution together and it is estimated that for every ton of cement, approximately one ton of carbon dioxide is produced.

The team of scientists from the University of Cambridge has found a clever way to avoid those emissions.

It takes advantage of the fact that you can reactivate used cement by exposing it to high temperatures again.

The chemistry is well established and has been widely performed in cement kilns.

The breakthrough is to prove this is possible by piggybacking on the heat generated by another heavy industry: steel recycling.

When you recycle steel, you add chemicals that float on the surface of the molten metal to prevent it from reacting with the air and creating impurities. This is known as slugging.

The Cambridge team discovered that the composition of the cement used is almost exactly the same as the slag used in electric arc furnaces.

They trialled the process in a small-scale electric arc furnace at the Materials Processing Institute in Middlesbrough.

The BBC was present when the first high-quality, or “Portland,” cement was produced.

They call it ‘electric cement’ and describe the event as a world first.

The lead scientist, Cyrille Dunant, told the BBC that this could enable the production of carbon-free cement.

“We have shown that the high temperatures in the kiln reactivate the old cement and because electric arc kilns use electricity, they can be powered by renewable energy, making the entire cement production process carbon-free.”

He said this would also make steel recycling less polluting, as making the chemicals currently used as slag also has high carbon costs.

Mark Miodownik, professor of materials and society at University College London, described the way the Cambridge team has combined cement and steel recycling as “genius” and believes if it can operate profitably at scale it could lead to huge reductions of cement and steel recycling. emissions.

“Can it compete with the existing infrastructure that will continue to pump cement into our lives in a very unsustainable way,” he wonders.

“Cement is already a multi-billion dollar industry. It’s David and Goliath we’re talking about here.”

The hope is that electric cement will be cheaper to produce because it essentially uses waste heat from the steel recycling process.

Spanish company Celsa will this week attempt to replicate the process in its full-arc furnace in Cardiff.

The Cambridge team estimates that, given current rates of steel recycling, their low-carbon cement could produce as much as a quarter of the UK’s demand.

But the use of electric arc furnaces is expected to increase in the future, potentially allowing more ‘electric cement’ to be produced.

And of course, the process could be duplicated around the world, potentially dramatically reducing cement emissions.