The production of concrete and steel is a major source of CO2 emissions, but a new solution from Cambridge could recycle both at the same time. Throwing old concrete into steel processing furnaces not only purifies the iron, but also produces “reactivated cement” as a byproduct. If carried out using renewable energy, the process could produce completely zero-carbon cement.
Concrete is the world's most widely used building material, and its manufacture is a particularly dirty business: concrete production alone is responsible for around 8% of total global CO2 emissions. Unfortunately, it is not easy to recycle them into a form that can be used to make new concrete structures.
Scientists have of course studied ways to make greener concrete. This may include modifying the recipe to replace the most polluting ingredients – especially limestone – or design the concrete so that it absorbs more CO2 from the air after its installation. For this new study, Cambridge researchers investigated how waste concrete could be converted back into clinker, the dry component of cement, ready for reuse.
“I had a vague idea, from previous work, that if it was possible to grind old concrete, removing the sand and stones, heating the cement, you would remove the water, and then it would form again clinker,” explains Dr Cyrille Dunant, first author of the study. “A liquid metal bath would facilitate this chemical reaction, and an electric arc furnace, used to recycle steel, seemed like a strong possibility. We had to try. »
An electric arc furnace needs a “fluxing” material, usually lime, to purify the steel. This molten rock substance captures impurities, then bubbles to the surface and forms a protective layer that prevents the pure new steel from being exposed to air. At the end of the process, the used flux is thrown away as waste.
Thus, for the Cambridge method, the lime flow was replaced by recycled cement paste. And sure enough, not only was he able to purify the steel perfectly, but if the remaining slag is cooled quickly in air, it becomes new Portland cement. The resulting concrete has similar performance to the original material.
Importantly, the team claims that this technique does not add major costs to the production of concrete or steel and significantly reduces CO2 emissions compared to usual methods of manufacturing both. If the electric arc furnace were powered by renewable sources, it could essentially produce zero-emission cement.
The technique has already been tested in kilns producing a few dozen kilograms of cement, and researchers say the first industrial-scale trials are underway this month, where it would produce around 66 tonnes of cement in two hours. Researchers say the process could be scaled up to produce a billion tonnes of “electric cement” by 2050.
“Producing zero-emission cement is an absolute miracle, but we also need to reduce the amount of cement and concrete we use,” said Professor Julian Allwood, who led the research. “Concrete is cheap, strong and can be made almost anywhere, but we simply use way too much of it. We could dramatically reduce the amount of concrete we use without any reduction in safety, but it takes a will policy to achieve this.
“As well as representing a major step forward for the construction industry, we hope that Cambridge Electric Cement will also be a flag to help the Government recognize that the opportunities for innovation in our journey to zero emissions extend far beyond. beyond the energy sector. A patent has been filed for the process, the first step towards commercialization.
The research was published in the journal Nature. The team describes the work in the video below.
The world's first process to produce zero-emission cement
Source: Cambridge University