Consider the following statements regarding calcined clay : 1. Its chief function is to impart strength and hydraulic properties of mortar. 2. It is dense, compact and impermeable concrete. 3. It increases the temperature of hydration and sets the concrete quickly. Which of the above statements are correct ?
- A2 and 3 only
- B1 and 2 onlyCorrect
- C1 and 3 only
- D1, 2 and 3
Solution
Concept
Calcined clay as a pozzolana
Step-by-step solution
1. Calcined clay is a pozzolanic material that combines with lime to give strength and hydraulic properties (statement 1 true). 2. It makes concrete dense and impermeable (statement 2 true). 3. Pozzolanas reduce the heat of hydration and slow the early setting, so statement 3 is false.
Explanation
Pozzolanic reaction is slow, so heat evolution is low. The products fill the pores and make concrete impermeable.
Why the other options are wrong
Options with statement 3 are wrong because calcined clay lowers the heat of hydration.
Shortcut
Pozzolana: low heat, dense, impermeable, slower early strength.
Common mistake
Thinking pozzolana speeds up setting.
Correct answer: B) 1 and 2 only