Climate change: UK breakthrough could slash cement CO2 emissions

Scientists say they’ve found a way to recycle cement from demolished concrete buildings.

Cement is the modern world’s most common construction material, but it is also a huge source of planet-warming gas emissions.

That is because of the chemical reactions when you heat limestone to high temperatures by burning fossil fuels.

Recycling cement would massively reduce its carbon footprint. Researchers say that if they switched to electric-powered furnaces, and used renewable energy like wind and solar rather than fossil fuels, that 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 binds the sand and aggregate in concrete together, and concrete is the most widely used material on the planet after water.

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

The problem is the material’s uniquely polluting chemistry.

It is made by heating limestone to up 1600 Celsius in giant kilns powered by fossil fuels.

Those emissions are just the start. The heat is used to drive carbon dioxide from the limestone, leaving a residue of cement.

Add both these sources of pollution together and it is estimated that about a tonne of carbon dioxide is produced for every tonne of cement.

The team of scientists, from Cambridge University, has found a neat way to sidestep those emissions.

It exploits the fact that you can reactivate used cement by exposing it to high temperatures again.

The chemistry is well-established, and it has been done at scale in cement kilns.

The breakthrough is to prove it can be done by piggybacking on 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 reacting with the air and creating impurities. This is known as slag.

The Cambridge team spotted the composition of used cement is almost exactly the same as the slag used in electric arc furnaces.