10 01 02

(Elbuaishi and Mangat, 2019)

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, 2021b).

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.

However, even with no ongoing domestic production, there are estimated to be stockpiles of more than 50 million tonnes of the material located across the UK (UKQAA, 2016) which are beginning to be re-utilised in order to supply demand for secondary materials for the cement and concrete industry. In 2019 over 900,000 tonnes of ash was sold from stockpiles, far exceeding the amount produced by operating coal power stations (UKQAA, 2019).

PFA is used as a pozzolanic, supplementary cementitious material (SCM) in the manufacture of concrete and cement. It contributes to the properties of the mix, particularly in resisting chloride-induced corrosion and minimising the risk of early stage cracking, whilst substituting a proportion the cement content required to achieve the desired strength. Along with GGBS (Ground Granulated Blast Slag, a by-product from steel production), PFA is one of the most widely available and established supplementary cementitious materials.