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Classes
Class C fly ash is created from burning coal that contains a large amount of calcium and a little carbon. Class F fly ash is created by burning low calcium coal that contains up to 10 percent carbon.
Uses
Both Class C and F are commonly used in concrete. According to an article published in Concrete Construction magazine, more than 50 percent of the exterior concrete in the United States contains fly ash. Interior concrete projects generally do not contain fly ash as it may produce surface stickiness, delayed hardening and shrinkage cracking. Fly ash is similar to but stronger than Portland cement.
Dangers
Electric energy plants in the United States produce millions of tons of fly ash. Fly ash contains heavy metals, such as arsenic, mercury and lead, making it a toxic waste product. Due to the toxicity of the byproduct, disposal of the overabundance of fly ash has become a problem.
Fly ash has been disposed of in landfills and used as landfill for places such as golf courses. When fly ash is used as landfill, it is buried under native soil. Over time, native soils erode and expose the fly ash. Fly ash used to construct one golf course in Virginia has caused ground water contamination in 200 wells within a half mile radius of the course. The water in these wells show elevated levels of arsenic, lead and aluminum. Aluminum in these wells has exceeded drinking water standards by 500 times in 2008, according to Robert McCabe, a writer for The Virginian-Pilot.