Question

A pozzolanic material must be composed mainly of
1. Microscopic silica
2. Microscopic and Amorphous silica
3. Microscopic and Crystalline silica
4. All of the above

Answer 1

Correct Answer - Option 2 : Microscopic and Amorphous silica

Concept: -

Pozzolana may be defined as a siliceous material that itself does not possess any cementitious properties but when reacts with lime in presence of lime forms compounds of low solubility having cementitious properties.

All pozzolanas are rich in silica and alumina and contain only a small quantity of alkalis.

The most commonly used pozzolans today are industrial by-products such as fly ash, silica fume from silicon smelting, highly reactive metakaolin, and burned organic matter residues rich in silica such as rice husk ash.

A pozzolanic material must be composed of microscopic and amorphous silica. As crystalline silica is not reactive with Portland cement which does not cause an alkali-silica reaction.