What is the purpose of adding gypsum to cement?

Gypsum (CaSO₄·2H₂O) is added to cement to slow down the process of setting.

Without gypsum, cement would set too rapidly (flash setting) when water is added, making it difficult to work with. Gypsum reacts with tricalcium aluminate (C₃A) in cement to form calcium sulfoaluminate (ettringite), which coats the C₃A particles and delays their rapid hydration.

This gives workers sufficient time to mix, transport, and place the concrete before it hardens.

The correct answer is To slow down the process of setting.