Which of the following is NOT a pozzolanic material?

• A. Portland cement
• B. Silica fume
• C. Fly ash
• D. Rice hull ash

Answer: (A)

Pozzolanic materials are siliceous or aluminosiliceous substances that, in the presence of water and the calcium hydroxide produced during cement hydration, react to form additional cementitious compounds like calcium silicate hydrate. They don’t cement on their own but enhance the strength and durability of concrete when blended with cement.

Silica fume provides reactive silica that participates in this pozzolanic reaction, improving the microstructure. Fly ash contains reactive silica and alumina and can act pozzolanically to form additional cementitious bonds. Rice hull ash is rich in silica and is used as a pozzolanic material as well. Portland cement, however, is a hydraulic cement that sets and gains strength through its own hydration of clinker minerals, not through a pozzolanic reaction. Therefore, the material that is NOT pozzolanic is Portland cement.