Climate change: UK breakthrough could reduce CO2 emissions

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Image caption, Scientists hope to clean up cement production

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

Cement is the most common building material in the modern 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 significantly reduce its carbon footprint. The researchers say that if they switch to electric furnaces and use renewable energy such as wind and solar instead of fossil fuels, it could mean no greenhouse gases at all.

And that would be a big deal. Cement forms the basis of the modern economy, both literally and metaphorically.

It is what binds the sand and aggregates in concrete, and concrete is the most widely used material on the planet after water.

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

The problem is the material’s unique polluting chemistry.

It is produced by heating limestone to 1,600 degrees Celsius in giant fossil fuel-fired kilns.

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

Add the two sources of pollution together and it is estimated that about one ton of carbon dioxide is produced for every ton of cement.

A team of scientists from the University of Cambridge has discovered a neat way to avoid these emissions.

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

The chemistry is well established and has been made at scale in cement kilns.

The breakthrough was to prove that it could be done by using 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 air and creating impurities. This is known as slag.

The Cambridge team noticed that the composition of the cement used was almost the same as the slag used in electric arc furnaces.

Image caption, Flames shoot from the top of an arc furnace as the material that will form the slag is added to the molten steel

They tested the process in a small electric arc furnace at the Materials Processing Institute in Middlesbrough.

The BBC was present when the first high grade or “Portland” cement was produced.

They call it “electric cement” and describe the event as a world first.

Lead scientist Cyril Dunant told the BBC that this could enable the production of zero-carbon 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, so the whole cement production process is decarbonised,” he said.

He said it also makes steel recycling less polluting, as producing the chemicals currently used as slag also has a high carbon cost.

Image caption, Dr Cyril Dunant, Lead Scientist on the Cement Project at the Materials Processing Laboratory in Middlesbrough

Mark Miodovnik, professor of materials and society at University College London, described the way the Cambridge team combined cement and steel recycling as “brilliant” and believes that if it can be made to work profitably at scale, it could lead to huge reductions in emissions.

“Can it compete with the existing infrastructure, which will very unsustainably continue to pump cement into our lives,” he asks.

“Cement is now a billion dollar industry. We are talking about David and Goliath here.

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

Spanish company Celsa will try to replicate the process at its full-scale electric arc furnace in Cardiff this week.

The Cambridge team estimate that, given current steel recycling rates, their low-carbon cement could produce up to a quarter of UK 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 drastically reducing cement emissions.

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