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Scientists say they 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 major source of planet-warming gas emissions.
This is due to chemical reactions when you heat limestone to high temperatures by burning fossil fuels.
Recycling cement would significantly reduce its carbon footprint. Researchers say that if they switched to electric stoves and used renewable energy like wind and solar instead of fossil fuels, it could mean no greenhouse gas emissions at all.
And that would be a big deal. Cement forms the foundation of the modern economy, literally and metaphorically.
This is what connects sand and aggregate in concrete, and concrete is the most widespread material on the planet after water.
It is also the main 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 chemistry of the material that pollutes the environment.
It is produced by heating limestone up to 1600 Celsius in huge furnaces powered by fossil fuels.
Those shows are just the beginning. The heat is used to drive the carbon dioxide out of the limestone, leaving behind a precipitate of cement.
Add up both of these sources of pollution and it is estimated that for every ton of cement, about a ton of carbon dioxide is produced.
A team of scientists from the University of Cambridge has found a convenient 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 produced in large quantities in cement kilns.
The breakthrough is to prove that this can be achieved 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 forming impurities. This is known as slag.
The team from Cambridge observed that the composition of the cement used was almost exactly the same as the slag used in electric arc furnaces.
They trialled the process in a small 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 described the event as a world first.
The chief 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 furnaces use electricity, they can be powered by renewable energy, so the entire cement production process is decarbonized,” he said.
He said it also makes steel recycling less polluting because the production of chemicals currently used as slag also has a high carbon cost.
Mark Miodownik, professor of materials and society at University College London, described the way the Cambridge team combined cement and steel recycling as “genius” and believes that if it can be made to work profitably on a large scale, it could lead to to large emission reductions.
“Can it compete with the existing infrastructure that will very unsustainably continue to pump cement into our lives,” he asks.
“Cement is already a billion-dollar industry. We are talking about David and Goliath here.”
Electric cement is hoped to 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 electric arc furnace in Cardiff this week.
The Cambridge team estimate, given current steel recycling rates, that their low-carbon cement could produce as much as a quarter of UK demand.
However, 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 worldwide, potentially dramatically reducing emissions from cement.