Question

Gypsum is added to cement in order to:

• A. prolong hydration
• B. increase strength after hydration
• C. decrease heat of hydration
• D. reduce curing time

Answer 1

The correct option is A prolong hydration

Gypsum is called the retarding agent of cement which is mainly used for regulating the setting time of cement and is an indispensable component. Without gypsum, cement clinker can condense immediately by mixing with water and release heat. The major reason is that C3A in the clinker can dissolve in water quickly to generate a kind of calcium aluminate hydrate, a clotting agent, which will destroy the normal use of cement. The retardation mechanism of gypsum is: when cement is hydrated, gypsum reacts with C3A quickly to generate calcium sulfoaluminate hydrate which deposits and forms a protection film on the cement particles to hinder the hydration of C3A and delay the setting time of cement.