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Fly ash is a waste product of the combustion of coal. It is produced at coal-fired power plants and blast furnaces. It may be substituted for as much as 35% of the cement in some concrete mixes. Its use has been widespread in very large projects for many years, however smaller local concrete suppliers are now beginning to offer it more routinely.
For each pound of fly ash used instead of cement, one pound of carbon dioxide emissions will be saved. A concrete floor slab for a typical two-car garage would contain approximately 4,000 lbs. of cement; therefore substituting 25% fly ash would save 1,000 pounds of carbon dioxide. This is equal to the emissions from an average automobile for one full month!
Using the 1,000 pound of fly ash will save enough energy to power the average American home for 12 days, and save enough landfill space for the solid waste generated by an average American for over 200 days!