Fly ash, formerly regarded as a coal power waste material was collected and stockpiled. Now, it is considered environmentally and economically advantageous to maximise commercial use of this by product. Worldwide the total consumption of fly ash exceeds 60%, although this figure can approach 100% in specific regions. For example, cement products containing up to 50% fly ash provide an enhanced construction material. Inclusion of ash in cement is one of the most significant industrial means to reduce carbon intensity in the construction industry due to the high energy demand of cement manufacture.
Global changes to the coal power industry are reflected in fly ash production, which is dominated by Asia, while there are shortages in the USA and Western Europe. International fly ash exports from Asia and Eastern Europe are currently estimated at US$100 million per year. Amid rising demand, the market price of fly ash has risen and is currently one third that of cement.
The varied industrial applications of fly ash include:
- Construction and engineering materials: concrete, bricks, blocks and geopolymers. Incorporation of ash into construction materials leads to a product possessing enhanced strength that is especially important in complex engineering projects such as bridge, tunnel and dam structures, and as a structural road-fill material.
- Agriculture: ash possessing low levels of contaminants is suitable for agricultural use, to improve key soil indicators such as carbon content, water retention and fertility.
- Mineral extraction: The extraction of valuable elements (such as rare earths and germanium) from fly ash is significant to the renewable energy and aerospace industries, while fly ash can also be a source of aluminium.
- Advanced materials: composites, ceramics, fillers, zeolites and proppants. Fly ash is increasingly applied in the manufacture of advanced composite materials to extend the material properties and replace valuable metals.
Beneficial uses of coal fly ash
Dr Ian Reid, Anne M Carpenter, Dr Alice Masili