Current Affairs Questions

Explanation :

Context: Recently, National Thermal Power Corporation(NTPC) Ltd. has started to collaborate with cement manufacturers across the country to supply fly ash as part of its endeavour to achieve 100% utilisation of the by-product produced during power generation.

About Fly Ash

• Fly ash is a fine powder that is a byproduct of burning pulverized coal in electric generation power 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 collected from the exhaust gases by electrostatic precipitators or bag filters.
• All fly ashes exhibit cementitious properties to varying degrees depending on the chemical and physical properties of both the fly ash and cement.
• Fly ash includes substantial amounts of Silicon Dioxide (SiO2), Aluminium Oxide (Al2O3), Ferric Oxide (Fe2O3) and Calcium Oxide (CaO).

Types

Fly ash is classified as either Class C or Class F ash based on its chemical composition.

• 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). Class C ash is also referred to as high calcium fly ash because it typically contains more than 20 per cent 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 also present. Class F, or low calcium fly ash has less than 10 percent CaO.

Applications

• Fly ash can be used as prime material in many cement-based products, such as poured concrete, concrete block, and brick.
• One of the most common uses of fly ash is in Portland cement concrete pavement.