cambridge researchers discover the world’s first process to produce zero-emissions cement

Recycled cement can produce new, low-emission concrete

Researchers from the University of Cambridge have found a way to produce very low-emission concrete on a commercial scale using recycled concrete and electrically-powered arc furnaces. Since the latter is employed for steel recycling, steel can also be recycled during the process of recycling cement. From here, the Cambridge researchers discovered that used cement can be a substitute for lime flux to produce recycled cement, and then this recycled cement can be used to make new low-emission concrete.

Lime flux is a component in steel recycling that helps remove impurities, but often, it ends up being a waste product in the manufacturing process. To avoid the increase in waste, used cement might take over its position with its recyclability property, which can help make low-emission concrete at a commercial level. This new method of cement recycling doesn’t add any significant costs to concrete or steep production, the Cambridge researchers say. Instead, they can help reduce carbon emissions from both concrete and steel because of the reduced need for lime flux.

video stills and images courtesy of Cambridge University, via Youtube and Materials Processing Institute

Cambridge researchers heat up crushed recycled materials

Study author Dr. Cyrille Dunant from the Department of Engineering at the University of Cambridge explains that crushing old concrete can help take out the sand and stones. Then, heating it up can remove the water mixed in. ‘It would form a clinker again,’ the researcher says. For context, 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.

‘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,’ adds Dr. Cyrille Dunant. The clinkering process needs heat and the right combination of oxides, all of which are in used cement, but they also need to be reactivated. The researchers tested a range of lime flux made from demolition waste and added lime, alumina and silica, and these were processed in the Materials Processing Institute’s EAF with molten steel and rapidly cooled.

In the end, the Cambridge researchers found the combination of cement clinker and iron oxide. ‘We found the combination of cement clinker and iron oxide is an excellent steelmaking slag because it foams and it flows well,’ says Dr. Cyrille Dunant. ‘And if you get the balance right and cool the slag quickly enough, you end up with reactivated cement, without adding any cost to the steelmaking process.’

Cambridge researchers have found a way to produce very low-emission concrete using recycled concrete

Scientists unveiled that cement in concrete can be replaced

Researchers from the University of Cambridge, comprising Cyrille F. Dunant, Shiju Joseph, Rohit Prajapati, and Julian M. Allwood, state that concrete is made from sand, gravel, water, and cement, which serves as a binder. Cement can contribute to around 90 percent of concrete emissions even though it makes up only a small portion of the concrete mixture. Concrete is also the second most used material on Earth after water, responsible for around 7.5 percent of the total carbon emissions on the planet.

Because of this, the Cambridge researchers strove to find a way to reduce concrete emissions by making it with recycled cement. Scientists have already discovered that half of the cement in concrete can be replaced with alternative materials, including fly ash. The issue is that these alternatives need chemicals to work and harden the cement, which may not be as helpful to the environment as one might think. To find a functional alternative, the researchers attempted to first crush old concrete.

used cement can be a substitute for lime flux to produce recycled cement

For the Cambridge researchers, finding out how to produce low-emission concrete using recycled cement is an ‘absolute miracle.’ A challenge industries should keep in mind is to reduce the amount of cement and concrete used. For Professor Julian Allwood of Cambridge’s Department of Engineering, who led the published study, varied industries are using concrete far too much. It is cheap, strong, and can be made almost anywhere, which may contribute to much of its usage.

‘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,’ says the professor. As of publishing the story, the Cambridge researchers have filed a patent on the process to support their finding’s commercialization. The research was supported in part by Innovate UK and the Engineering and Physical Sciences Research Council (EPSRC), part of UK Research and Innovation (UKRI). Julian Allwood is a Fellow of St Catharine’s College, Cambridge.

recycled cement then can be used to make new low-emission concrete