Which material is often used as a supplementary cementitious material?

Fly ash is a byproduct of coal combustion in power plants and is commonly used as a supplementary cementitious material in concrete production. Its inclusion in concrete not only enhances the strength and durability of the final product but also contributes to overall sustainability. By partially replacing Portland cement with fly ash, the environmental impact of concrete production is reduced because it decreases the amount of cement needed, which in turn lowers carbon emissions associated with cement manufacturing.

Fly ash improves workability, reduces permeability, and can lead to a reduction in the heat of hydration, making it particularly beneficial for large-scale concrete pours. Its pozzolanic properties allow it to react with calcium hydroxide in the presence of water, forming additional calcium silicate hydrate, which helps to increase the strength of the concrete over time.

Other materials mentioned have different functions: gravel serves as coarse aggregate and is not a supplementary material, steel fibers are used to enhance the toughness and impact resistance of concrete, and water is simply a mixing agent that facilitates the chemical reactions of cement but does not provide the pozzolanic properties characteristic of supplementary cementitious materials.