Hi Rick,

Thanks for your question on manufacturing bricks using fly ash. This is a great opportunity to provide a sustainable “green” product that is used on a daily basis while saving precious landfill space. There were nearly 42 million tons of unused fly ash disposed of in 2008 according to the American Coal Ash Association’s Coal Combustion Production Use and Survey Report, which would occupy approximately 27,500 acre feet (33,900,000 m3) of landfill space according to the US EPA.

Some of the concerns with bricks made of fly ash have been failure and pop outs. “This happens when the bricks come into contact with moisture and a chemical reaction occurs causing the bricks to expand.”

There are several methods of producing bricks from fly ash, according to www.flyashbrickinfo.com. There are clay fly ash bricks, where the brick is a mixture of 60% fly ash and clay. These bricks are then fired in a kiln at about 1000 degrees C, which is not a very sustainable process. Next there are fly ash – sand lime bricks where the fly ash mixes with lime at ambient temperature while the brick cures, which is a greener manufacturing process than that of the clay fly ash bricks.

Henry Liu invented a green fly ash brick that “generates microscopic bubbles in the hardened brick that better accommodate the expansion of freezing water” and “could withstand over 100 freeze-thaw cycles.” Liu’s manufacturing process “uses a waste by-product rather than clay, and solidification takes place under pressure rather than heat; it has several important environmental benefits. It saves energy, reduces mercury pollution, alleviates the need for landfill disposal of fly ash, and costs 20% less than traditional methods.”

In closing, I wouldn’t be concerned as much about the best “machine” to produce bricks made with fly ash as I would be concerned about the manufacturing process. It’s clear that a process that includes a kiln burning at 1000 degrees C for hours to fire a brick is less sustainable than a process where the brick cures at ambient temperature. More than likely the process that is more sustainable is more economical as well, as demonstrated by Henry Liu. For those reasons, I would choose manufacturing fly ash bricks using that type of method.

Good Luck!

Dave

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