Q.91 As a precaution in cold weather concreting, cement containing _______ should be selected.
- Ahigher C3S and higher C2S
- Bhigher C3S and lower C2SCorrect
- Clower C3S and lower C2S
- Dlower C3S and higher C2S
Solution
Concept
In cold weather, concrete needs fast heat of hydration and early strength. C3S gives this, and C2S is slow.
Step-by-step solution
1. In cold weather, hydration is slow and fresh concrete can freeze. 2. We need cement that gives quick heat and quick early strength. 3. C3S hydrates fast, gives high heat and early strength, so choose higher C3S. 4. C2S hydrates slowly, gives low heat and late strength, so choose lower C2S. 5. So the answer is higher C3S and lower C2S, option B.
Explanation
Cold weather slows the setting and hardening of concrete. Cement with more C3S produces more heat and gains strength quickly, which protects concrete from frost damage. Less C2S is preferred because it reacts slowly and gives low early heat.
Why the other options are wrong
A: Higher C2S gives slow strength gain and less early heat. C: Lower C3S reduces early heat and early strength. D: This is low-heat cement, suitable for hot weather or mass concrete, not cold weather.
Shortcut
Cold weather needs heat, so use high C3S (fast) and low C2S (slow).
Common mistake
Choosing low C3S and high C2S, which is the rule for hot weather or mass concreting.
Correct answer: B) higher C3S and lower C2S