Definition
Produced in a coal combustion power plant, Fly Ash is the non-combustible mineral portion of coal. Its particles are smooth as glass, sphere-shaped, usually finer than cement particles.
In the past, Fly Ash was normally released into the atmosphere via the smoke stack, but pollution control equipment mandated in recent decades now require that it be captured prior to release.
Usage
Fly Ash is normally used to as an addition to Portland cement in concrete production because it supplies technological and economical benefits.
Additionally to economic and ecological advantages, Fly Ash in concrete increases its workability, reduces separations and permeability, and improves sulfate resistance.
Its usage also includes:
Embankments and structural fill
Waste stabilization and solidification
Raw feed for cement clinkers
Mine reclamation
Stabilization of soft soils
Road subbase
Flowable fill
Mineral filler in asphalted concrete
Typical Composition
| Component | Bituminous | Subbituminous | Lignite |
| SiO2 (%) | 20-60 | 40-60 | 15-45 |
| Al2O3 (%) | 5-35 | 20-30 | 20-25 |
| Fe2O3 (%) | 10-40 | 4-10 | 4-15 |
| CaO (%) | 1-12 | 5-30 | 15-40 |
| LOI (%) | 0-15 | 0-3 | 0-5 |