Question

What is the purpose of adding gypsum to cement? 

• A. To give a hard mass
• B. To facilitate the hydration of cement
• C. To slow down the process of setting
• D. To speed up the process of setting

Answer 1

The Correct Option is C

Gypsum (CaSO$_4\cdot$2H$_2$O) is added to cement to regulate the setting time. Without gypsum, cement would set immediately upon mixing with water, leaving no time for concrete placement.

Gypsum reacts with tricalcium aluminate (C$_3$A) in cement to form insoluble calcium sulfoaluminates, which slows down the hydration reaction.

This delay ensures sufficient time for the mixing, transportation, and placement of concrete before it hardens.