Hello Kannan, thanks for your question about fly ash bricks.

How to Make Fly Ash Bricks

The recipe for fly ash bricks includes class C fly ash, Sand/Stone dust, Lime, Gypsum, water, and Cement. It is compressed at 4,000 psi and cured for 24 hours in a 150 °F (66 °C) steam bath, then toughened with an air entrainment agent. As a safety measure, always keep out of contact with eyes.

The bricks last for more than 100 freeze-thaw cycles.

Environmental Benefits of Fly Ash Bricks

As you may know, using fly ash is just one type of eco-cement. “Eco-cementing” is when materials such as fly ash and petroleum coke are used in cement to prolong the life of local raw materials and fuel reserves. Using pozolan and fly ash can also be a substitute for clinker.

Using fly ash bricks in your building is advantageous for several reasons. The process of manufacturing fly ash bricks saves energy (thus reducing greenhouse gas emissions), reduces mercury pollution and costs less when compared to traditional brick manufacturing.

As discussed in a previous green-buildings.com article, “What Is Fly Ash?: Fly Ash Bricks as a Recycled Material for LEED”, recycling fly ash for use as bricks helps reduce fly ash waste. This waste is typically dumped in landfills, which have limited capacity, or retention ponds, which can be dangerous if the fly ash’s toxins leak into the groundwater.

As green building gains popularity, producers of these alternative materials are much more common. Many businesses establish relationships with suppliers who keep an inventory of blended cements that they can choose from.

Is Fly Ash Toxic?

It is important to note that the use of fly ash has been increasingly controversial. While the EPA does not consider fly ash a hazardous material, it contains mercury, lead, arsenic, barium, and other potentially dangerous substances.

In fact, there was an episode of 60 Minutes that questioned whether fly ash is safe to use. As you can see in a previous green-buildings article, Fly Ash Cement: Should I Believe 60 Minutes? How Dangerous Is It?, it is questionable whether the environmental benefits of using fly ash outweigh the potential hazards of using it as a building material.

In fact, during January 2011 USGBC public comment period, Public Employees for Environmental Responsibility (PEER) urged the USGBC to revoke LEED credits for fly ash use. PEER claimed that using fly ash in buildings was ultimately a “brown act”, and that coal plants should handle wastes more responsibly rather than recycling fly ash in buildings.

So far, the LEED credit has not been adjusted to reflect this opinion – but we should stay tuned for updates from USGBC.

It is also important to note that coal ash, which some may confuse with fly ash, is toxic and be very dangerous if leaked into groundwater or inhaled.

Fly Ash Bricks as a Recycled Material for LEED

A LEED project can earn points for using fly ash bricks. Specifically, this would earn points in Materials & Resources (MR) Credit 4, Recycled Materials.

As far as I know, LEED does not plan on removing fly ash as an acceptable “recycled material” for MR Credit 4, as I mentioned above. However, it is best to stay tuned for updates from USGBC on this subject.

Related Advice:

• Fly Ash: Safer than Portland Cement?



• What is Fly Ash?: Fly Ash Bricks as Recycled Material for LEED



• Fly Ash Brick: What's the Best Way to Manufacture it?