Question

Gypsum is added to cooled clinker during cement manufacture:
$(a)$ Because gypsum permits formation of the fine powder
$(b)$ To delay the initial setting time of cement
$(c)$ To increase the hardening of cement
$(d)$ To increase the strength of set concrete

Answer 1

Hint – In this question use the concept that gypsum is a mineral and is hydrated calcium sulfate (CaSO4.2H2O) in chemical form and it plays a very vital role in controlling the rate of hardening of the cement. Use this concept to figure out why gypsum is added to the cooled clinker.
Gypsum is a mineral and is hydrated calcium sulfate (CaSO4.2H2O) in chemical form.
Gypsum plays a very important role in controlling the rate of hardening of the cement.
During the cement manufacturing process, upon the cooling of the clinker, a small amount of gypsum is introduced during the final grinding process.
Gypsum is added to control the “setting of cement”.
If not added, the cement will set immediately after mixing of water leaving no time for concrete placing.
Therefore gypsum is added to delay the initial setting time of cement.
Hence option (B) is the correct answer.

Note – Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate. It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, blackboard/sidewalk chalk, and drywall. Main purpose of adding gypsum in the cement is to slow down the hydration process of cement once it is mixed with water. The process involved in hydration of cement is that, when the water is added into cement, it starts reacting with C3A and hardens.