Question

Consider the following statements;
Low percentage of $C_{3}S$ and high percentage of $c_{2}S$ in cement will result in

1. higher ultimate strength with less heat generation
2. rapid-hardening
3. better resistance to chemical attack
Which of these statements are correct?

• A. 1 and 3
• B. 2 and 3
• C. 1 and 3
• D. 1, 2 and 3

Answer 1

The correct option is C 1 and 3

$C_{3}S$ and $C_{2}S$ together constitute about 70%-80% of the cement and control most of the strength giving properties. Upon hydration both give the same product called calcium silicate hydrate $\left(C_3{S}_2{H}_3\right)$ and calcium hydroxide. Tricalcium silicate $\left(C_{3}S\right)$ having a faster rate of reaction is accompanied by greater heat evolution develops early strength. On the other hand, dicalcium silicate $\left(C_{2}S\right)$ hydrates and hardens slowly and provides much ultimate strength. $C_{2}S$ provide more resistance to chemical attack. Thus a higher $C_{3}S$ percentage results in rapid hardening with early gain in strength at a higher heat of hydration. On the other hand, higher $C_{2}S$ percentage results in slow hardening, less heat of hydration, higher ultimate strength and greater resistance to chemical attack.