A new process can utilize construction waste to produce cement. Researchers say that by 2050, this method could reduce billions of tons of carbon emissions. The related paper was recently published in "Nature."
"We have clearly demonstrated that cement can be recycled to make cement," said Julian Allwood from the University of Cambridge in the UK. "We are moving towards producing zero-carbon emission cement, which is truly remarkable."
British researchers have, for the first time, produced cement in an electric arc furnace. Image source: Materials Processing Institute
The cement production industry is a significant source of pollution, accounting for 7.5% of total greenhouse gas emissions. So far, there have been no known methods for large-scale cement production that do not impact the climate.
Cement production requires "clinker," which is made by heating a mixture of raw materials such as limestone and clay to 1450 degrees Celsius. The high temperatures and chemical reactions involved in clinker production result in carbon emissions, with clinker production contributing to 90% of the total carbon footprint of cement production.
Allwood and colleagues have developed an alternative method for producing clinker, which involves reusing cementitious slurry extracted from demolished buildings. Its chemical composition is similar to a lime-based flux, which is used to remove impurities from recycled steel.
As steel melts, the flux made from old cement forms a slag floating on top of the recycled steel in the furnace. Once ground into powder, the slag is equivalent to clinker and can be used to produce Portland cement, the most common form of cement.
If the recycled steel and cement are produced in electric furnaces powered by renewable energy or nuclear power, the process has almost zero carbon emissions. "This method is really quite simple," says Allwood.
Laboratory experiments have proven the effectiveness of this process. The team estimates that it provides a "transitional" solution that can be used alongside traditional equipment, potentially reducing emissions by up to 3 billion tons of carbon dioxide annually if adopted globally.
The research team is currently conducting industrial trials in collaboration with Cambridge Electric Cement Company and construction companies like Balfour Beatty and Tarmac. Allwood states, "In the coming weeks, we will start a series of trials to produce 30 tons of cement per hour."
Scaling up the new cement production process depends to some extent on the availability of recycled steel. Currently, steel recycling accounts for about 40% of global steel production. Allwood suggests that over the next 30 years, as the industry decarbonizes, production could double and possibly triple.
However, there are still challenges ahead. The recycled cement process requires furnace temperatures of 1600 to 1750 degrees Celsius, slightly higher than traditional cement production. Leon Black from the University of Leeds in the UK mentions that this will increase electricity costs.
Other challenges include establishing a supply chain for old cement, attracting necessary capital investments, and convincing this cautious industry to adopt the new process on a large scale.
Black notes, "They have overcome one obstacle by producing a material with the same composition as Portland cement. The devil is in the details - energy requirements, logistics, and scaling up."
For more information, refer to the related paper: https://doi.org/10.1038/s41586-024-07338-8
