The compound of Portland cement which reacts immediately with water and also sets first is

ANS:C - Tri-calcium aluminate

Answer is correct as we add gypsum in cement to slow down the reaction of c3A if gypsum is not added then cement would flash set in 5-10 mins. Tricalcium aluminate (C3A) is mostly related to the heat of hydration.

Functions of Dicalcium Silicate:-
1. Hardens slowly.
2. It effects on strength increases occurs at ages beyond one week.
3. Responsible for long-term strength.

Functions of Tricalcium Aluminate:-
1. Contributes to strength development in the first few days because it is the first compound to hydrate.
2. It turns out the higher heat of hydration and contributes to faster gain in strength.