Why is gypsum added to clinker in cement production?

Gypsum is added to clinker during cement production primarily to control the setting time of the cement. When water is added to the cement mix, it starts to hydrate and set, which is a chemical reaction that eventually leads to solidification. By incorporating gypsum, the formation of ettringite is promoted during the early stages of hydration. This action effectively slows down the setting time, allowing for better workability and manipulation of the material before it hardens.

For practical applications, a longer setting time is beneficial as it gives engineers and construction workers more time to place and finish the concrete without it setting too quickly. This is crucial for large pours or intricate work where adjustments may need to be made after the initial mixing.

Though gypsum can influence strength and durability indirectly by ensuring better hydration of the cement particles, its primary role remains in regulating the setting time of the cement. Consequently, the addition of gypsum ensures that the cement can be used effectively in a variety of construction applications without the risk of premature setting.