Fly ash is the fine ash produced in the furnaces of coal-fired power stations. The ash is a by-product from the combustion of pulverised coal at very high temperatures and pressures producing steam required for power generation.
This fine or ‘fly’ ash is a mineral rich substance that cools and solidifies into rounded, glassy particles in the flue gases, which are carried upwards and captured by either electrostatic or mechanical precipitators.
The Fly ash particles are extremely fine and resemble cement in appearance. They are also chemically similar to cement, containing the same basic oxides in differing proportions and mineralogy. Most importantly, fly ash demonstrates pozzolanic properties in concrete i.e. the fly ash has the ability to react with the lime released by hydrating Portland cement to produce extremely robust and durable cementitious hydrates.