Question

What is the role of gypsum, $CaSO_{4}.2H_{2}O$ in setting of cement ? Identify the correct option from the following :

• A. to fasten the setting process
• B. to provide water molecules for hydration process
• C. to help to remove water molecules
• D. to slow down the setting process

Answer 1

The Correct Option is D

The role of gypsum in the setting of cement is an important aspect of its chemistry. Gypsum, which is chemically known as calcium sulfate dihydrate (\(CaSO_{4}.2H_{2}O\)), is added to cement for specific reasons. Let us explore the options and determine the correct answer:

Option: To fasten the setting process

Explanation: Gypsum is not added to cement to fasten the setting process. In fact, it serves the opposite role.

Option: To provide water molecules for the hydration process

Explanation: While gypsum contains water in its structure (dihydrate), its primary purpose is not to provide water molecules for hydration.

Option: To help to remove water molecules

Explanation: Gypsum does not help in removing water molecules. This option is incorrect.

Option: To slow down the setting process

Explanation: This is the correct option. Gypsum is added to cement to slow down the setting process. Without gypsum, the cement would set very quickly after adding water, which is not desirable for workability and proper placement. By slowing down the setting process, gypsum allows for more workable time and ensures that the cement mix can be used effectively in construction.

Conclusion: Hence, the correct answer is that gypsum is used to slow down the setting process of cement. This delay in setting time is crucial for ensuring that the cement remains workable for a sufficient period, allowing for proper mixing, placing, and finishing.