Question

Gypsum is added to cement because:
(A) It makes the cement very hard
(B) It increases the pace of setting of cement
(C) It slows down the initial setting of cement when water is added
(D) None of the above

Answer 1

To answer this question, you must recall the properties of gypsum. It plays a very important role in the process of setting or hardening cement. It increases the time for setting of cement.

Complete answer:
Now we must understand what happens when gypsum is added to cement.
When cement is manufactured, clinkers are formed in the process. These clinkers of cement after cooling are added with some amount of gypsum. This mixture of the clinkers and gypsum is then sent for the final grinding process. The main function of gypsum in the mixture is to control and slow down the process of hydration of cement after mixing with water. This controls the setting or hardening of the cement. If gypsum is not added to cement, the cement would harden almost immediately after water is mixed which does not leave any time for the transport, mixing and placement of concrete or other substances over wet cement. As a result, due to the addition of gypsum, the cement remains workable and plastic for a longer duration as gypsum alters the formation of cement and forms crystals that are very small to bridge gaps between cement particles. So, it slows down the initial setting of cement when water is added.
Thus, the correct answer is C.

Note:
Gypsum is a naturally occurring mineral that is obtained as a raw material from the deposits formed by ancient seabeds. It is a hydrated salt of calcium sulphate known as copper sulphate dihydrate due to the presence of two molecules of water of crystallization. Gypsum has a variety of uses in various fields like manufacturing, industrial and agricultural purposes.