Question

Consider the following compounds of cement: 
(A) C\(_2\)S 
(B) C\(_4\)AF 
(C) C\(_3\)S 
(D) C\(_3\)A 
The correct sequence of these compounds in the decreasing order of rate of hydration is:

• A. (D), (C), (B), (A)
• B. (D), (B), (C), (A)
• C. (B), (A), (D), (C)
• D. (A), (B), (C), (D)

Hint:

Cement hydration rates are highest for C\(_3\)A and C\(_3\)S, which are responsible for early strength gain.

Answer 1

The Correct Option is A

Step 1: Understanding Hydration of Cement Compounds.
The rate of hydration of cement compounds varies. The compounds react with water and produce heat. The rate of hydration of these compounds is in the order: C\(_3\)A (Alite)>C\(_3\)S (Belite)>C\(_4\)AF (Ferrite)>C\(_2\)S.
Step 2: Analysis of the Options.
- (A) C\(_2\)S: This compound hydrates at a slower rate and contributes less to the early strength of concrete.
- (B) C\(_4\)AF: Hydrates at a moderate rate.
- (C) C\(_3\)S: Hydrates faster and contributes significantly to the early strength of concrete.
- (D) C\(_3\)A: This compound hydrates very quickly and generates a significant amount of heat, contributing to the early strength.

Step 3: Conclusion.
The correct sequence, in the decreasing order of rate of hydration, is: (D) C\(_3\)A, (C) C\(_3\)S, (B) C\(_4\)AF, (A) C\(_2\)S, making option 1 the correct answer.

Final Answer: \[ \boxed{1. \, (D), (C), (B), (A)} \]