How Cambridge Electric Cement Is Making Concrete More Sustainable

Cement and concrete are vital building blocks of our modern society. Its abundance, durability, and versatility make it a widely used construction material. The only downside is that producing cement, an essential component of concrete, is carbon-intensive. Annually we produce about 5 billion tonnes of the stuff, contributing around 8% of carbon dioxide emissions.

Because of this, researchers have been finding ways to cut emissions from cement by replacing some of it with other materials, such as engineered timber, or using additives to reduce the amount of cement. Some cement manufacturers attempt to capture carbon at their factories and bury it underground. However, these solutions only partially solve the problem of making cement production less carbon-intensive.

Why is cement so carbon-intensive?

According to The Economist, the reason lies in the chemistry of how it’s made. “The key ingredient is limestone, which is mainly calcium carbonate. It contains both oxygen and carbon. The limestone is mixed with silica-bearing clay and other materials and then heated in a rotating kiln to more than 1,400ºC. A calcination chemical reaction drives the carbon from the limestone, producing lime. The carbon then combines with oxygen to form the unwanted carbon dioxide.”

Heating the limestone with other ingredients under intense heat produces a clinker, which is then milled into a fine powder known as cement.

Half of the emissions from cement making come from the calcination process and a half from quarrying the limestone and heating the kiln. This means that each tonne of cement made also emits a tonne of carbon dioxide.

Thankfully, three Cambridge engineers, Dr Cyrille Dunant, Dr Pippa Horton and Professor Julian Allwood, who also founded Cambridge Electric Cement, found a way to circumvent the chemistry of calcination by recycling old cement from demolished buildings.

According to the University of Cambridge News:

“The inspiration for Cambridge Electric Cement struck inventor Cyrille Dunant when he noticed that the chemistry of used cement is virtually identical to that of the lime-flux used in conventional steel recycling processes. The new cement is therefore made in a virtuous recycling loop that not only eliminates the emissions of cement production but also saves raw materials and even reduces the emissions required in making lime-flux.”

“The new process begins with concrete waste from the demolition of old buildings. This is crushed to separate the stones and sand that form concrete from the mixture of cement powder and water that bind them together. The old cement powder is then used instead of lime-flux in steel recycling. As the steel melts, the flux forms a slag that floats on the liquid steel to protect it from oxygen in the air. After the recycled steel is tapped off, the liquid slag is cooled rapidly in air and ground up into a powder which is virtually identical to the clinker, which is the basis of new Portland cement. In pilot-scale trials of the new process, the Cambridge team has demonstrated this combined recycling process, and the results show that it has the chemical composition of a clinker made with today’s process.”

The research has been awarded a grant by the Engineering and Physical Sciences Research Council in the amount of £1.7m to allow the inventors to collaborate with Dr Zushu Li at Warwick University and Dr Rupert Myers at Imperial College and to reveal the underlying science behind the new process.

The new grant will fund an additional team of researchers to probe the range of concrete wastes that can be processed into Cambridge Electric Cement, evaluate how the process interacts with steelmaking, and confirm the performance of the resulting material.

Professor Allwood said, ‘If Cambridge Electric Cement lives up to the promise it has shown in early laboratory trials, it could be a turning point in the journey to a safe future climate. Combining steel and cement recycling in a single process powered by renewable electricity could secure the supply of the basic construction materials to support the infrastructure of a zero-emissions world and enable economic development where it is most needed.”

The Economist reports that the team has made tens of kilograms of their recycled, zero-carbon cement so far.

The results are promising, says Philippa Horton, another of the company’s founders says that the results are promising.

A potential challenge is that the quantity of cement produced will depend on how much can be recovered from demolishing old buildings, bridges, roads and the like, as well as on the availability of electric-arc furnaces.

However, Dr Horton is optimistic that one day Britain will be able to produce enough cement to meet a quarter to a half of its total demand.