Fly Ash

Explanation :

• Fly ash is a byproduct from burning pulverized coal in electric power generating plants. During combustion, mineral impurities in the coal (clay, feldspar, quartz, and shale) fuse in suspension and float out of the combustion chamber with the exhaust gases. As the fused material rises, it cools and solidifies into spherical glassy particles called fly ash.
• It is considered pozzolanic, which means it’s a siliceous and aluminous material reacts with calcium hydroxide to form a cement.
• There are two common types of fly ash: Class C and Class F.
• Class C ashes are generally derived from sub-bituminous coals and consist primarily of calcium alumino- sulfate glass, as well as quartz, tricalcium aluminate, and free lime(CaO).It is also referred to as high calcium fly ash because it typically contains more than 20 percent CaO.
• Class F ashes are typically derived from bituminous and anthracite coals and consist primarily of an alumino-silicate glass, with quartz, mullite, and magnetite. It is also low calcium fly ash has less than 10 percent CaO.

Source: Civil Services Chronicle Online