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An alliance of construction and property giants is hoping to kickstart development of greener concrete by pledging to buy only concrete with net-zero carbon emissions by mid-century.

A crucial material in cities and the built environment, concrete is responsible for 8 per cent of global CO2 emissions. Emissions from cement, the glue that holds concrete together, were .

Now a group of 17 companies, including , �����Ի���, have formed a coalition pledging that one-third of the concrete they use by 2025 will be a low-emission version, rising to one-half by 2030. They also intend to use only net-zero concrete by 2050. The group is modelled on previous initiatives for and that were designed to show there is market demand for lower carbon options.

“Concrete is a huge part of global emissions. What we are aiming to do is put a really big collective demand signal there, which gives confidence to innovators, to investors. It’s about saying the market is coming for zero carbon solutions, and we’re ready to buy it,” says at Climate Group, the non-profit organisation that has organised the campaign.

The problem with decarbonising concrete is there are currently no solutions on a large enough scale. The chemical process of making cement is inherently carbon-intensive and usually requires huge amounts of fossil fuel-powered heat. However, researchers and companies are making progress, such as and so less concrete is needed to build a given structure.

There are also efforts to develop technology to capture and store the carbon released when limestone is heated and crushed to make cement. Clarkson says there will be a role for carbon capture and storage (CCS), but downplays how big it will be: “CCS has not been proven yet, we don’t have it at scale. It comes into that kind of, ‘don’t worry, we’ll wave a magic wand’ sort of category.”

of property developer Joseph Homes, one of the initiative’s founders, says in the short term people are looking to cut concrete emissions by using fly ash, a by-product of coal power stations, as a replacement for some of the cement in the concrete. But fly ash deposits are finite and declining, so innovations will be needed long term. He says volcanic ash may offer a fly ash alternative and points to start-ups such as California-based , which is using concrete to store CO2. “It’s going to cost more in the short term,” he says of buying low-carbon concrete, but he thinks some of that extra cost could be offset by design choices that use less of the material.

“I don’t think there are a huge number of direct alternatives to Ordinary Portland Cement [one of the most widely used type of cement],” says at Imperial College London. He thinks focusing on developing carbon capture and storage to decarbonise the cement might be more sensible – although he adds that the initiative to lower emissions from concrete is “a good idea in general”.

Part of the alliance’s job will be to define what “net-zero concrete” means, as there is no universally accepted standard. Clarkson says she hopes the new initiative will be followed by similar alliances in China and India, where demand for concrete is high.