RP1004: State of Practice: High Volume Applications of Fly Ash and Barriers to Commercialisation

Australia is heavily reliant upon the use of coal for electric power generation with approximately 74.9% or 170,822 GWh of electricity in year 2010 to 2011 being generated through coal-fired power plants. Australia’s coal powered generators produce about 14 million tonnes of fly ash per year. Currently, only 42% of by-product fly ash is used in various construction-related applications and the remainder placed into onsite storage dams or dumped into landfill sites potentially causing serious environmental issues. The principal aims of this study are to review the existing fly ash utilisation industry and to examine the potential high volume applications of fly ash.

The widespread utilisation of Geopolymer concrete in the industry is certainly the most promising pathway to increase the rate of fly ash utilisation. Geopolymer concrete is the result of the reaction of materials containing aluminosilicate such as fly ash with alkalis to produce an inorganic polymer binder. As there is no Portland cement in geopolymer concrete mix and geopolymer binder can provide reduction of embodied CO₂ of up to 80% compared to Ordinary Portland Cement. Indeed, carbon emissions due to the manufacture of Portland cement are second only to burning fossil fuels. Its share of CO₂ emissions in Australia is estimated at 8 million tonnes/year.

The considerable sustainability benefits of using a geopolymer binder system composed almost entirely of recycled materials has led to considerable research on geopolymer concrete (GC) in recent years in Australia and three established commercial suppliers of GC: Wagners in the Queensland supplying Earth Friendly Concrete (EFC), Zeobond in Victoria supplying the E-crete technology and Rocla, part of Fletcher Building group with their Head Office in Chatswood, New South Wales. Geopolymer concrete has yet to enter the mainstream of concrete construction. The main barriers for widespread adoption of geopolymer concrete in the industry and the pathway to overcome those barriers have been clearly identified and are reported in the CRC-LCL RP1004-I (Berndt et al., 2013). 

Fly ash based manufactured synthetic lightweight aggregate for concrete appears to be the second most promising pathway to increase significantly the rate of fly ash utilisation. Lightweight concretes offer superior insulation properties that can reduce energy consumption in buildings, reduce the dead weight and material handling cost in construction. Further, the rapid depletion of quality natural aggregate quarry sources close to most major metropolitan regions of Australia, emphasize why the need to explore alternative economic sources has become imperative to support increasing vital infrastructure development, including housing, roads, bridges, schools and hospitals.