The main use of fly ash in concrete. This is a strong added value because it can replace part of the cement. Key benefits include:

+ Part of the cement can be replaced by fly ash while the final strength remains the same or is even higher. Because of this savings can be made on the raw materials cost of concrete. Due to the later participation of fly ash in the hydration reaction of cement, the initial strength however is lower.

+ The replacement of Portland cement (CEM I) also means that the "carbon footprint" of concrete is reduced. The production of Portland cement costs about 0.7 to 0.9 tonnes of CO₂ per tonne, depending among others on the efficiency of the cement factory. The CO₂ emissions from a CEM III/B is 0.22 tonnes CO₂ per tonne of cement.

+ The spherical shape of fly ash particles has a positive influence on the workability, allowing in many cases for a slight reduction of the water cement ratio while maintaining the same workability.

+ Fly ash has a beneficial effect on the durability of concrete. The sensitivity of concrete to the alkali-silica reaction clearly decreases due to the binding of calcium hydroxide by the glassy phase. This is demonstrated in many scientific articles and recognised in legislation (e.g. CUR-Recommendation 89).

+ Due to the ongoing pozzolanic reaction, the pore size decreases over time, causing the oxygen diffusion resistance of the concrete to increase. This is a measure of the resistance to penetration of aggressive substances. It is therefore less susceptible to corrosion of reinforcement and chemical attack from outside. More information can be found in the CUR-rapport 2000-2.pdf 'Duurzaamheid van beton met poederkoolvliegas in de praktijk'.

In using fly ash in combination with CEM I a k-value of 0.4 may be used, in conformity with NEN-EN. In practice this means that 1 kg of fly ash may replace 0.4 kg of cement. For CEM III the k-value is 0.2. Application can also be done through an attestation arrangement. In that case a significantly higher replacement value will be attributed to fly ash. This goes up to the replacement of 1 kg of cement by 1 kg of fly ash!

Usually a few percent of fine powder is added to asphalt mixtures to influence the behaviour of bitumen. Important properties are its inertia (low water solubility) and binding capacity.

Fly ash contains a significant proportion of aluminium. This makes it a popular material for the production of Portland clinker. This is a half product in the manufacture of in particular Portland cement (CEM I) and blast furnace cement (CEM III). It replaces other aluminium sources such as clay.

The chemical composition, melting properties and fineness make fly an attractive raw material for coarse ceramics.