Cambridge engineers develop new greener concrete which could help in drive toward net zero

A researcher holds a sample of the greener concrete
A researcher holds a sample of the greener concrete Credit: University of Cambridge

Engineers have already created self-healing concrete and developed the ability to print structures with it, but up until now they've failed to make it green.

And they've had a long time to try, the material has been around since before Caesar was a lad, the Coliseum in Rome was built using concrete.

It is ubiquitous, from being used to create the National Theatre in London and the UEA in Norwich it is the second-most-used material on the planet after water.

Concrete The Coliseum was built during the reign of Emperor Vespasiano in c.72 AD Credit: PA Images

But despite being beloved of architects and builders, it is not exactly environmentally-friendly.

It is responsible for approximately 7.5% of total human-produced CO₂ emissions. So

So to borrow from Ralph Waldo Emerson, develop a better concrete, and the world will beat a path to your door.

Brushing off their doormat are researchers from the University of Cambridge who say for the first time they've developed a method to produce very low-emission concrete at scale – an innovation that could be transformative in the transition to net zero.

The Cambridge researchers found that used cement is an effective substitute for lime flux, which is used in steel recycling to remove impurities and normally ends up as a waste product known as slag.

By replacing lime with used cement, the end product is recycled cement that can be used to make new concrete.

The cement recycling method developed by the Cambridge researchers, reported in the journal Nature, does not add any significant costs to concrete or steel production and significantly reduces emissions from both concrete and steel, due to the reduced need for lime flux.

Professor Julian Allwood from Cambridge’s Department of Engineering, who led the research, said: “We held a series of workshops with members of the construction industry on how we could reduce emissions from the sector.

“Lots of great ideas came out of those discussions, but one thing they couldn’t or wouldn’t consider was a world without cement.”

Concrete facts

Why is so bad for the environment?

Concrete is made from sand, gravel, water, and cement, which serves as a binder. Although it’s a small proportion of concrete, cement is responsible for almost 90% of concrete emissions.

Cement is made through a process called clinkering, where limestone and other raw materials are crushed and heated to about 1,450°C in large kilns. This process converts the materials into cement, but releases large amounts of CO₂ as limestone decarbonates into lime.

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Are there any alternatives?

Over the past decade, scientists have been investigating substitutes for cement, and have found that roughly half of the cement in concrete can be replaced with alternative materials, such as fly ash, but these alternatives need to be chemically activated by the remaining cement in order to harden.

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Sounds easy then... is it?

Not quite as Prof Julian Allwood explains.

“It’s a question of volume – we don’t physically have enough of these alternatives to keep up with global cement demand, which is roughly four billion tonnes per year,” said Allwood.

“We’ve already identified the low hanging fruit that helps us use less cement by careful mixing and blending, but to get all the way to zero emissions, we need to start thinking outside the box.”

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Fellow Cambridge academic Dr Cyrille Dunant, described how they came up with the new greener solution: “I had a vague idea from previous work that if it were possible to crush old concrete, taking out the sand and stones, heating the cement would remove the water, and then it would form clinker again.

“A bath of liquid metal would help this chemical reaction along, and an electric arc furnace, used to recycle steel, felt like a strong possibility. We had to try.”

The Cambridge Electric Cement process has been scaling rapidly, and the researchers say they could be producing one billion tonnes per year by 2050, which represents roughly a quarter of current annual cement production.

“Producing zero emissions cement is an absolute miracle, but we’ve also got to reduce the amount of cement and concrete we use,” said Prof Allwood. “Concrete is cheap, strong and can be made almost anywhere, but we just use far too much of it. We could dramatically reduce the amount of concrete we use without any reduction in safety, but there needs to be political will to make that happen.

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