The move to clean energy is, ironically, jeopardising the main sources of low-carbon cement alternatives that are a by-product of burning fossil fuels.
Two products in particular will be affected: Fly ash — a by-product of coal-fired power plants — and ground granulated blast-furnace slag (GGBS), which is derived from coke-based steel manufacturing. These materials have been effective in reducing the carbon content of concrete, with GGBS in particular frequently used in major construction projects.
In recent years, the construction industry has turned to SCMs to decrease the amount of cement used in concrete. Cement production is responsible for a substantial amount of carbon emissions globally.
But the availability of these materials is expected to fall in the future, reports UK concrete industry body, the Concrete Centre, which provides best practice guidance, events and online resources to help the UK economy realise the potential of concrete.
Speaking to the Centre, Professor Leon Black of Leeds University explains: “With the decarbonisation of electricity — and UK steel manufacture shifting to electric steel recycling furnaces — SCMs will become increasingly scarce.”
UK clay as an alternative to traditional SCMs
The Concrete Centre says that, to address the impending shortage, a team of researchers is investigating the potential of UK clays as alternative SCMs. The project, known as Eureka, is funded by the Engineering and Physical Sciences Research Council (EPSRC).
Professor Black is working alongside Professor Hong Wong from Imperial College London and Clive Mitchell from the British Geological Survey. Their goal is to determine the extent to which UK clays can be processed and used as SCMs.
The team is focusing on lower-grade clays as potential alternatives to metakaolin, an expensive SCM derived from china clay.
Prof Black stresses the importance of this research: “It might be usable as an SCM rather than simply for landscaping.
BGS maps clay distribution for Eureka Project
The BGS is playing a crucial role in mapping the distribution of suitable clays across the UK. It has already analysed approximately 60 clay samples from various locations, and says around a dozen samples “show promising characteristics”.
To make clay suitable for use as an SCM, it needs to undergo a process called calcination. This involves heating the clay to around 800°C to make it reactive. While this process does have a carbon cost, it is significantly lower than that of traditional cement production.
Prof Black explains the environmental benefits of using calcined clay as an SCM: “You end up with an SCM with a carbon footprint roughly half that of Portland cement,” he says. “This reduction in carbon emissions could have a substantial impact on the construction industry’s overall environmental footprint.”
