Question

Assertion A: Pozzolana is added to cement to increase early strength.

Reason R: It reduces the heat of hydration.

Which of the following is correct?

1. A is true but R is false.
2. Both A and R are true, and R is the correct explanation of A
3. A is false but R is true
4. Both A and R are true, but R is not a correct explanation of A

Answer 1

Correct Answer - Option 3 : A is false but R is true

Explanation:

Pozzolana cement:

• Pozzolanic cement is mixtures of Portland cement and a pozzolanic material that may be either natural or artificial. The natural pozzolanas are the main materials of volcanic origin but include some diatomaceous earth. Artificial materials include fly ash, burned clays, and shales.
• It generates less heat of hydration than ordinary Portland cement.

• It is economical as in PPC a part of the costly clinker of OPC is replaced by cheaper pozzolanic material.

• Used in hydraulic structures, marine structures, construction near the seashore, dam construction etc.

To increase the early strength of cement, Tri-calcium silicate (C3S) is increased. Hence Pozzolona is not added to increase early strength.