Climate change: UK breakthrough could cut cement CO2 emissions

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 also a major source of planet-warming gas emissions.

The reason for this is 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 figuratively.

It binds sand and aggregates together in the concrete. After water, concrete is the most commonly used material on earth.

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, accounting for 7.5% of man-made CO2.

The problem is the material’s unique, environmentally harmful chemistry.

It is made by heating limestone to up to 1,600 degrees Celsius in huge fossil-fuel-powered furnaces.

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

If you add these two sources of pollution together, you get an estimate that around 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 avoid 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 from another heavy industry – steel recycling.

Steel recycling involves adding chemicals that float on the surface of the molten metal, preventing it from reacting with the air and forming contaminants. This slag is called dross.

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 there when the first high-quality cement, called “Portland cement,” was produced.

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 would also reduce pollution from steel recycling, as the production of the chemicals currently used as slag also has a high carbon content.

Mark Miodownik, professor of materials and society at University College London, described the way the Cambridge team combined cement and steel recycling as “brilliant”. He is convinced that this could lead to enormous emissions reductions if this process could be implemented profitably on a large scale.

“Can it compete with the existing infrastructure that continues to pump cement into our lives in a highly unsustainable way?” he asks.

“Cement is already a billion-dollar industry. We’re talking about David and Goliath.”

It is hoped that electro-cement will be cheaper to produce as it essentially uses the 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 meet up to a quarter of the UK’s demand given current steel recycling rates.

However, it is expected that the use of electric arc furnaces will 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.