A new eco‑friendly method recycles concrete using renewable energy

According to "Nature," researchers from the United Kingdom have developed a new method of recycling concrete from demolished buildings, employing a process similar to steel production.

Concrete, produced by combining cement, aggregate (such as sand and/or gravel), and water, is currently the most widely used building material. It is essential for large-scale investment projects, such as constructing a nuclear power plant, which requires about 1.3 million cubic yards of concrete and accompanying infrastructure. However, the production of cement, a key component of concrete, is associated with the emission of enormous amounts of greenhouse gases.

The primary sources of these emissions are chemical reactions that occur when limestone is heated to 2,642 degrees Fahrenheit in enormous rotary kilns powered by fossil fuels. High temperatures release carbon dioxide from the limestone. About one ton of carbon dioxide is released for every cement produced from fossil fuels and limestone. Global cement production is four billion tons annually, accounting for 7.5 percent of human-generated CO2 emissions.

However, scientists at Cambridge University have developed a new recycling method that allows for the recovery of cement from old concrete by heating it. According to them, this method would significantly reduce the carbon footprint associated with cement production. If kilns powered by electricity sourced from wind and solar energy were used instead of fossil fuels, greenhouse gas emissions associated with cement production could be eliminated.

The key to this method could be the heat generated during steel recycling. Chemicals added to the scrap steel during smelting, such as limestone, float on the surface of the molten metal as slag, preventing reaction with the air and the formation of impurities.

Scientists from Cambridge have noted that concrete's composition is very similar to that of slag in electric arc furnaces. So far, the method of processing old concrete has been successfully tested in a slight arc furnace at the Materials Processing Institute in Middlesbrough.

Cyrille Dunant, the lead scientist involved in the project, told the BBC that this method could enable the production of cement without carbon dioxide emissions. "We have shown the high temperatures in the furnace reactivate the old cement and because electric arc furnaces use electricity they can be powered by renewable power, so the entire cement making process is decarbonised," Dunant explained.

By combining concrete recycling with steel recycling, the environmental impact of steel production could also be reduced, as the output of fluxes currently involves high carbon dioxide emissions.

The Spanish company Celsa plans to attempt to replicate this new process in its full-scale electric arc furnace in Cardiff this week.

Scientists at Cambridge claim that their low-emission cement could meet up to one-quarter of the UK's demand for this material by 2050. With the broader use of electric furnaces, it could constitute an even greater portion of global cement demand.