Good quality cement contains higher percentage of

Solution (By Examveda Team)

Option A: Tri-calcium silicate (C3S) - This is the most important compound in cement.
It's responsible for the early strength development (within the first week).
A higher percentage of C3S means faster setting and hardening, which is generally desired in good quality cement.

Option B: Di-calcium silicate (C2S) - This contributes to strength gain over a longer period (after the first week).
While important, it's not the primary factor determining early strength and overall cement quality as much as C3S.

Option C: Tri-calcium aluminate (C3A) - This contributes to very early hydration and heat generation.
A high percentage of C3A can lead to flash set and reduced durability, especially in sulfate-rich environments.
Good quality cement generally has a controlled amount of C3A, not a higher percentage.

Option D: Tetra calcium alumino ferrite (C4AF) - This reduces the clinkering temperature during cement production.
It has minimal contribution to the strength of cement.

Therefore, the correct answer is: Option A: Tri-calcium silicate, as it contributes to faster setting and hardening and higher early strength of the cement.