The implementation of a zero-carbon cement production process has the potential to greatly decrease emissions in the construction industry.

A new technology could use waste from demolished buildings to produce cement, which researchers say could save billions of tonnes of carbon by 2050.

“We have definitely proven that we can recycle cement into cement,” he says. julian allwood at Cambridge University. “We are moving towards producing cement with zero emissions, which is amazing.”

Cement production is highly polluting, accounting for 7.5 percent of total greenhouse gas emissions, but until now there was no known way to produce cement on a large scale without impacting the climate.

Producing cement requires “clinker,” which is made by heating a mixture of raw materials such as limestone and clay to 1450°C (2650°F). Both the heat and chemical reactions required to make clinker generate carbon emissions, and clinker production accounts for 90 percent of cement's total carbon dioxide emissions.

Allwood and colleagues have developed an alternative process for making clinker that reuses cement paste from demolished buildings. This paste has the same chemical composition as lime flux, a substance used to remove impurities from recycled steel.

As the steel melts, the flux made from the old cement forms a slag that floats on top of the recycled steel. When ground into powder, slag is the same as clinker. It can then be used to make Portland cement, the most common cement.

When the recycled steel and cement are produced using electric furnaces powered by renewable or nuclear energy, the process produces almost no emissions. “The idea is very simple,” Allwood says.

Laboratory tests prove the process works, providing a “drop-in” solution that can be used with conventional equipment, and the team calculates that a global switch to the process could save up to three gigatons of carbon dioxide per year.

The team is now working on industrial trials through spin-out company Cambridge Electric Cement, with partners including construction companies Balfour Beatty and Tarmac. “We will be commencing a series of trials in the coming weeks to produce 30 tonnes of batches per hour,” Allwood says.

Scaling up new cement manufacturing processes relies in part on growth in recycled steel production, which currently accounts for about 40% of global steel production. Allwood says production rates will at least double and likely triple over the next 30 years as the industry decarbonises.

However, some challenges lie ahead. The recycled cement process requires furnace temperatures of 1,600-1,750°C (2,900-3,200°F), which are slightly higher than traditional cement production. As this increases electricity costs, Leon Black At the University of Leeds, UK.

Other hurdles include establishing a supply chain for waste cement, attracting needed capital investment and persuading a notoriously wary industry to adopt the new process at scale.

“They've overcome one barrier in terms of creating a material that has the same composition as Portland cement,” Black says. “The devil is in the details: the energy requirements, the logistics, the scale.”