Why pozzolanic materials are used

Pozzolanic materials are added to lime (and cement) for the following reasons.

1. They react with free lime to form insoluble calcium silicates and aluminates, giving hydraulic properties to fat lime so that it can set under water and in damp places.
2. They increase the strength and durability of mortar and concrete, and improve resistance to sulphate and chemical attack.
3. They give a low heat of hydration, which is useful in mass concrete such as dams.
4. They reduce permeability and lower the cost, since fly ash, surkhi and ash are cheap by-products.
5. They improve workability and reduce bleeding.
6. They save cement and help the environment by using waste material.