Concrete is the second most-consumed material in the world (second only to water) and accounts for 8% of the global CO2 emissions. Cement is the major source of emissions in concrete – up to 75% of concrete emissions (i.e. 245 kg CO2 per m3 of concrete). Many concrete manufacturers have opted to substitute Fly Ash (FA) or Granulated Blast Furnace Slag (GBFS) instead of cement (fully or partially). These cementitious materials are by-product waste of other processes; FA from the burning of coal in power plants and GBFS from iron and steel production. Using FA or GBFS in concrete can improve the workability and durability of concrete. In addition, one of the most desirable functions of these cementitious materials is to reduce a significant amount of concrete embodied carbon.
UK government reports  indicate the industries providing FA and GBFS are under transition to eliminate these materials. This transition is a result of national and global developments, such as the Glasgow & Paris Agreements on Climate Change. These changes have a direct impact on the availability of FA and GBFS for the cement and concrete sector.
Fly Ash (FA) supply chain the UK and Europe
The UK will phase out its coal power stations by 2025. Furthermore, electricity from coal power stations will fall by 83% in the EU by 2030 , as most countries have set similar commitments to phasing out coal. According to the latest government report , there has been a shortage of FA in the UK since 2016 and its availability continues to decline. This dearth has also resulted in a sharp increase in the price of FA.
Granulated Blast Furnace Slag (GBFS) supply chain in the UK and Europe
Many blast furnaces in the EU and the UK are also at the end of their lifespans. These furnaces will be substituted by greener alternatives i.e. Electric Arc Furnace technology which does not produce GBFS . Electric Arc Furnaces currently produce 28% of the steel in the world; however, they only account for 8% of the steel industry’s emissions . A shortage of GBFS has been experienced in the UK since 2016 and is expected to become much worse by 2025. This has resulted in importing of blast furnace slag. The scarcity of GBFS will continue to increase its price.
The global supply of FA and GBFS is shrinking, while the main consumers of concrete in the world (China and India) have started utilising FA and GBFS. For example, India has designed its net-zero program to maximise the consumption of GBFS in their cement production (Arcelor Mittal Nippon Steel deal ). In summary, the shortage of FA and GGBS and their increasing cost will affect the decarbonisation of the construction industry.
FA and GBFS are vital for some applications of concrete (i.e. increasing the durability). These materials are very effective in reducing the embodied carbon of concrete. However, due to the shortage of FA and GGBS, they are not a viable solution for the decarbonisation of concrete in the long term.