Cement and Concrete - Benefits and Barriers in Coal Ash Utilisation
AUTHOR: Irene M Smith
DATE: January 2005
The coal combustion products industry is facing major challenges despite decades of beneficial utilisation of coal ash in a wide variety of applications. Fly ash is especially affected by recent trends towards greater implementation of NOx control systems which may increase the carbon and ammonia in ash. Cocombustion with greater proportions of secondary fuels, such as biomass, also results in more varied ash. Fly ash is often produced to tight specifications for applications in the cement and concrete industries.
The requirements need to be broadened to include all potential markets for a wider range of fly ash specifications. Fly ash utilisation is hindered where it is regarded as a waste or by-product. This report summarises recent trends in coal ash utilisation in different countries. It then focuses on two major sectors of fly ash utilisation: cement and concrete. Requirements for many different uses of fly ash are compared. The engineering and environmental benefits of using fly ash are investigated for each sector. These include greater long term strength and durability, CO2 emissions reduction, and saving primary aggregates. Barriers to utilisation occur in marketing, handling, transport and storage, through increased carbon or ammonia in ash, the effects of cofiring with secondary fuels and through the potential for mercury release from fly ash.
These are being overcome by various means in the utilisation sectors or are under investigation. Continued use of fly ash in traditional markets is helped by draining and drying stockpiled fly ash, classification, separation and burnout processes. Total use of fly ash is the aim of new combined processes to produce high-grade and expensive materials for various specialised applications. Cement and concrete – benefits and barriers in coal ash utilisation.