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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 huge source of global 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. The researchers say that if they switched to electric furnaces and used renewable energy sources such as wind and solar rather than fossil fuels, it could mean that no greenhouse gases would be released at all.
And that would be a big deal. Cement forms the basis of the modern economy, literally and metaphorically.
It’s what binds the sand and aggregate in concrete together, and concrete is the second most 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 behind China and the US, responsible for 7.5% of human-produced CO2.
The problem is the material’s uniquely polluting chemistry.
It is made by heating limestone up to 1600 Celsius in giant fossil fuel kilns.
Those emissions are just the beginning. The heat is used to drive the carbon dioxide out of the limestone, leaving the cement residue behind.
Add up both of these sources of pollution and it is estimated that about a ton of carbon dioxide is produced for every ton of cement.
A team of scientists from the University of Cambridge has found a neat way to bypass 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 carried out on a large scale in cement kilns.
The breakthrough is to prove that this can be achieved by tapping into 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 Cambridge team found that the composition of the cement used was almost exactly the same as the composition of the slag used in electric arc furnaces.
They tested the process in a small electric arc furnace at the Materials Processing Institute in Middlesbrough.
The BBC was present at the production of the first high quality cement or “Portland” cement.
They call it “electric cement” and described the event as a world first.
Lead scientist Cyrille Dunant told the BBC it could enable the production of zero-carbon cement.
“We have shown that high temperatures in the kiln reactivate old cement, and because electric arc furnaces use electricity, they can be powered by renewable energy sources, so the entire cement production process is decarbonised,” he said.
He also said that recycling steel is 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 “brilliant” and believes that if they can make it work profitably at scale, it could lead to huge reduction of emissions.
“Can it compete with the existing infrastructure that will pump cement into our lives in a very unsustainable way,” he asks.
“Cement is already a billion dollar industry. We’re talking about David and Goliath here.”
The hope is that electric cement will be cheaper to make 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 that, given current steel recycling rates, their low-carbon cement could produce up to 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 replicated around the world, potentially dramatically reducing emissions from cement.