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Scientists say they have found a way to recycle cement from demolished concrete buildings.
Cement is the modern world’s most common building material, but also a major source of planet-warming gas emissions.
This is due to the chemical reactions that occur when limestone is heated to high temperatures by burning fossil fuels.
Recycling cement would massively reduce its carbon footprint. Researchers say if they switched to electric-powered ovens and used renewable energy like wind and solar instead of fossil fuels, it could mean no greenhouse gases would be released at all.
And that would be a big deal. Cement forms the foundation of the modern economy, both literally and metaphorically.
It is what holds the sand and aggregates in concrete together, and concrete is the most commonly used material on the planet after water.
Cement is also one of the main drivers of climate change. If cement were a country, it would be the third largest source of emissions after China and the United States and responsible for 7.5 percent of human-caused CO2.
The problem is the material’s unique, environmentally harmful chemistry.
It is produced by heating limestone to temperatures of up to 1,600 degrees Celsius in huge furnaces powered by fossil fuels.
These emissions are just the beginning. The heat is used to drive carbon dioxide out of the limestone, leaving behind a cement residue.
When these two sources of pollution are added together, it is estimated that about one ton of carbon dioxide is produced per ton of cement.
The team of scientists at the University of Cambridge has found a clever way to circumvent these emissions.
This takes advantage of the fact that used cement can be reactivated by exposing it to high temperatures again.
The chemistry is well established and has been carried out in large-scale cement kilns.
The breakthrough aims to prove that this is possible by harnessing the heat of 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 contaminants. This is called slag.
The Cambridge team found that the composition of the used cement matched almost exactly the slag used in electric arc furnaces.
They tested the process in a small arc furnace at the Materials Processing Institute in Middlesbrough.
The BBC was present when the first high quality cement, or ‘Portland’ cement, was made.
They call it “electric cement” and describe the event as a world first.
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, decarbonizing the entire cement manufacturing process,” he said.
He said it also makes steel recycling less harmful to the environment, as producing 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 combined cement and steel recycling as “brilliant” and believes it could lead to huge savings if done on a large scale Scale works profitably emissions.
“Can it compete with the existing infrastructure that will continue to 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.”
The hope is that electrocement will be cheaper to produce because it essentially uses waste heat from the steel recycling process.
Spanish company Celsa will attempt to replicate the process at its fully equipped electric arc furnace in Cardiff this week.
The Cambridge team estimates that their low-carbon cement could produce up to a quarter of the UK’s needs given current steel recycling rates.
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 around the world, potentially dramatically reducing cement’s emissions.