What is Fly Ash, and How is it Used in Construction?

Fly ash is a fine, powdery material that is a byproduct of burning pulverized coal in thermal power plants. It consists mainly of silica, alumina, iron oxide, and calcium oxide. This byproduct, when properly processed and utilized, can significantly improve concrete strength, durability, and sustainability.

Composition and Types of Fly Ash

Fly ash is classified into two main types based on its chemical composition:

Class F Fly Ash

• Derived from bituminous and anthracite coal.
• Contains low calcium content (<10‰).
• Possesses pozzolanic properties, requiring a cementing agent such as lime or Portland cement.
• Ideal for high-performance concrete applications.

Class C Fly Ash

• Produced from lignite and sub-bituminous coal.
• Has a higher calcium content (>10‰).
• Can act as a self-cementing material without the need for additional binders.
• Used in road construction, structural concrete, and soil stabilization.

Production and Processing of Fly Ash

Fly ash is collected from electrostatic precipitators or baghouses in power plants before the gases are released into the atmosphere. It is then processed to remove impurities and ensure consistency in particle size and chemical composition.

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