The EPA declares fly ash and silica fume as hazardous substances
The EPA has long been a supporter of fly ash and silica fume as additions to concrete mixtures. These substances have been widely utilized in the construction industry as well as in ICF construction. Silica fume and fly ash are by-products of the coal industry and their use in buildings has long been promoted as a sustainable and cheap way to reduce the impact of coal use. The EPA has long touted the ‘beneficial reuse’ of coal power plant waste, but its support of fly ash and silica fume was rescinded in 2011.
The change of heart was brought about, according to the EPA, because of fears that the heavy metal content of these substances may be hazardous. Studies are underway to determine the extent of the threat to building occupants and the biggest producers of coal waste Boral Material Technologies and Headwater Resources, have taken the matter to court. The EPA is refusing to lift it’s classification of the materials as ‘hazardous’ until the studies have been completed, saying: “We must err on the side of caution and classify coal ash as hazardous until the studies are completed.”
Fly ash and Silica Fume
Fly ash is a by-product of the process of burning coal to produce electricity. About 43 percent (430 million tons) of fly ash is recycled into the green building industry each year. Electrostatic precipitators and scrubbers remove the product from the exhaust gases. The fine, tan-coloured powdery substance consists almost completely of silica. From the EPA:
“Fly ash is a pozzolan, a siliceous material which in the presence of water will react with calcium hydroxide at ordinary temperatures to produce cementitious compounds. Because of its spherical shape and pozzolanic properties, fly ash is useful in cement and concrete applications. The spherical shape and particle size distribution of fly ash also make it a good mineral filler in hot mix asphalt applications and improve the fluidity of flowable fill and grout when it is used for those applications.”
Silica Fume is also a by-product of the coal industry and has been added to cement to improve its resilience. From Norchem, the largest producers of silica fume products in North America: “Long service life, durability and the potential to withstand catastrophic events, silica fume concrete will provide excellent resilience, furthering the cause of sustainability.”
Impact on the Green Building Industry
The ban on fly ash and silica fume will have an enormous impact on the green building industry where it enjoys widespread use. The products are currently used in everything from concrete to wall boards and bricks. In some applications, fly ash can constitute up to 25% of cement content. Its use has, to date reduced the production footprint of cement significantly, made coal production more environmentally sustainable and taken care of the by-products too.
While the building industry waits to hear the verdict on fly ash and silica fume, studies are going ahead to determine if the heavy metal content has any adverse effects on building occupants.