Question

Gypsum is added to clinker during cement manufacturing to:
(A) Decrease the rate of setting of cement
(B) Bind the particles of calcium silicate
(C) Facilitate the formation of colloidal gel
(D) All of the above

Answer 1

Hint: Recollect the manufacturing process of cement. Find out the molecular formula of gypsum. Gypsum is generally added to cement in order to increase the hardness of cement. Find out which of the options given in the question help in improving the hardness of cement to get the answer.

Complete step by step answer:
- Gypsum is a naturally occurring mineral. It is made up of calcium sulphate in hydrated form. Gypsum has the molecular formula, $CaS{{O}_{4}}.2{{H}_{2}}O$.
- During the process of manufacturing cement, there is formation of clinkers. These clinkers are allowed to cool and then mixed with a small amount of gypsum and then finally ground for the last time.
- Addition of gypsum to cement reduces the rate of hydration of cement once it is mixed with water.
- Therefore the main purpose of adding gypsum to cement is to decrease the rate of setting of cement.
- If gypsum is not added to cement then the cement will set or dry very quickly leaving no time for uniform placement of concrete and also, it will not have the desired hardness.
- Gypsum increases the hardness and the strength of the cement.
- Therefore, gypsum is added to the clinker during cement manufacturing to decrease the rate of setting of cement.
So, the correct answer is “Option A”.

Note: Remember gypsum is a naturally occurring mineral consisting of calcium sulphate dihydrate which is found in ancient seabed deposits. Gypsum is added to cement to reduce the rate of setting of cement by decreasing the rate of hydration and thus, imparts hardness and strength to the cement.