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(Glymond et al., 2018)

Coal was the fuel that drove the industrial revolution and since the mid nineteenth century, coal ash has been a major anthropogenic residue, produced in hundreds of billions of tonnes (MacBride, 2013).

In 2015, in response to the climate crisis, the UK government announced plans to close all coal power plants by 2025 (GOV.UK, 2015). As a result, there has been a reduction from coal providing 30% of the UK’s electricity generation needs in 2014 (DBEIS, 2015) to 2.9% in 2020 (DBEIS, 2021).

The level of coal ash produced in the UK has correspondingly reduced. Between 1999 and 2014, the UK’s coal power stations generated between 4 and 7 million tonnes of fly ash and up to 1 million tonnes of furnace bottom ash each year (UKQAA, 2016). By 2019 this figure had reduced to 257,454 tonnes (UKQAA, 2019) and this should be expected to reduce to zero by 2025.

FBA is most often utilised as a lightweight aggregate addition in the manufacturing of concrete blocks. In 2014, nearly 100% of the 800,000 tonnes of FBA that was produced in the UK was recycled in concrete block production (UKQAA, 2016). As the quantity of available FBA has reduced, block manufacturers have predominantly sourced alternative aggregates – though UKQAA figures from 2019 indicate that 57,000 of the waste material was actually imported (UKQAA, 2019) .