Fly Ash results from the combustion of pulverized coal and is a finely divided residue. It is basically generated in electric and steam generating plants. Coal is pulverized for generating a molten mineral residue known as Fly Ash. This molten mineral residue hardens in the initial stage and gets converted into ash. Fly ash is removed and extracted by the particulate emission control devices known as electrostatic precipitators.
Fly ash was earlier thought to be a waste product but when its benefits were recognized, till then fly ash is considered to be one of the most useful products for building and construction material. The main environmental benefits of fly ash when used as a construction material like in concrete includes-
• It enhances the durability of concrete to multiple times making the roads and other built structure using that concrete last lifelong
• Fly ash can replace manufactured cement totally and it is observed that it reduces the harmful air emissions, the amount of energy used and greenhouse gases.
• A significant reduction in products of coal combustion that are disposed of in landfills
• Conservation of natural resources and other materials.
• It makes the segregation of concrete easier and improves the strength.
• A cost-effective substitute for Portland cement.
• An environment-friendly substitute because of low embodied energy.
• Requires less water and is easier to use in extreme weather conditions.
• Produces concrete with a smooth surface and dense thickness.
• Has a great workability
• Decreases heat of hydration to a much extent
Fly ash is a pozzolan, this forms cement in presence of water and contains aluminous and siliceous material. The main chemical components present in fly ash are silicon oxide, aluminum oxide, iron oxide and sometimes calcium oxide also. When fly ash is mixed with lime and water, it makes it suitable for many building materials like blended cement, mosaic tiles, hollow blocks etc. Fly ash finds many applications in building and construction material but PCC pavement is the most common of it. It has many economic benefits.
There are two types of fly ash –
- Class F
- Class C
Class F- this type of fly ash decreases the risk of expansion which can be caused due to sulfate attack. Class f contains particles covered in a type of melted glass.
Class C – this type of fly ash is also resistant to expansion from an attack of many chemicals. It contains a much higher percentage of calcium oxide and is more commonly used.
Currently, many roads have been constructed using fly ash to increase their durability and reduce the construction cost. Amount of fly ash can be altered depending on the type of fly ash and its reactivity level. However, fly ash is still not used in interior works because of its inherent problems and challenges associated with it. What needs to be taken care of when adding fly ash, is the rate and uniformity of concrete hardening which ultimately influence the final finish. Fly ash has proven itself to increase the quality and durability of their products and this makes fly ash an important asset for concrete producers. Realizing its benefits in the near future, soon fly ash is going to be used in every building and construction material.
