Fly ash is the ash that "flies" into the chimneys of coal-burning power plants. It's one of the residues from burning coal and is usually considered to be a waste product. The specific composition of fly ash varies considerably, but it generally contains a substantial amount of silicon dioxide and calcium oxide. Fly ash may be disposed of in landfills or added to concrete to reduce the amount of the Portland cement need to make the concrete.
Instructions
1. Use Class F fly ash to make cement. This type of fly ash results from burning the older, harder coals known as bituminous coal and anthracite. The lime content of class F fly ash is below 10 percent and it contains alumina and silica.
2. Add a cementing agent to Class F fly ash. This type of fly ash has pozzolanic properties, meaning that it has a cement-like quality when combined with a proper cementing agent such as hydrated lime, Portland cement or quicklime.
3. Use Class C fly ash to make cement. This type of fly ash is produced by burning younger lignite and has some self-cementing properties. Class C fly ash does not require an activator and generally contains more than 20 percent lime. Cement made with Class C fly ash will harden and gain strength over time in the presence of water.
4. Compress a mixture of fly ash and water under 4,000 pounds per square inch and cure it in a steam bath at 150 degrees Fahrenheit for 24 hours. This technique produces fly ash brick, which can replace up to 50 percent of the Portland cement in concrete. In contrast, unprocessed fly ash can only replace 30 percent of the Portland cement in concrete.
5. Make asphalt concrete with fly ash. All types of fly ash may be used as a mineral filler in asphalt concrete mixes. Fly ash also improves the asphalt concrete's durability and resistance to rutting.
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