Types of Fly Ash

Detailed Classification of Fly Ash

1. Classification by Chemical Composition

• Class F Fly Ash
  Origin: Bituminous and anthracite coal
  Composition: Rich in silica, alumina, iron; low in calcium
  Characteristics: Pozzolanic
  Applications: Cement, bricks, mine backfill, road base stabilization
• Class C Fly Ash
  Origin: Lignite or sub-bituminous coal
  Composition: Higher calcium oxide
  Characteristics: Pozzolanic + Self-cementing
  Applications: Soil stabilization, cement replacement, structural fills

Source: FHWA

2. Classification by Location of Collection

• Dry Fly Ash: Collected via electrostatic precipitators; used in high-grade applications
• Wet Fly Ash (Pond Ash): Mixed with water, coarse and variable quality, used for embankments and land reclamation

3. Classification by Particle Size

• Micronized Fly Ash: Finer particles, high-performance applications
• Coarse Ash: Lower reactivity, typically landfilled or used as fill material

Additional Notes

Fly ash may contain trace heavy metals (arsenic, mercury, chromium, lead) and must be handled properly. It appears in various colors - light grey to brown - depending on the carbon content and coal source.

India ' s Fly Ash Generation

India is the third-largest electricity producer, heavily dependent on coal. In 2024, India generated 29.4 lakh metric tons of fly ash. The figure is projected to grow with increasing industrial energy demand.

Source: Monthly Abstract of Ash Generation and Utilization (Apr 2023 - Mar 2024)

Factors Affecting Fly Ash Generation

• Coal Composition: Indian coal contains 30 - 45% ash
• Power Generation: ~100-120 tons fly ash per GWh
• Technology: Efficiency improves but ash remains significant
• Boiler Type: Pulverized coal boilers produce 80% of fly ash; most commonly used