Which substance is used to retard the setting action of cement?
A
CaO
B
Al<sub>2</sub>O<sub>3</sub>
C
CaSO<sub>4</sub>.2H<sub>2</sub>O
D
Na<sub>2</sub>O + K<sub>2</sub>O
Correct Answer: CaSO<sub>4</sub>.2H<sub>2</sub>O
CaSO4.2H2O (Gypsum) is added to cement clinker to retard setting action of cement.