Cement is one of the most important building material of the present time. It is a dirty greyish heavy powder containing calcium aluminates and silicates. The important raw materials neede for the manufacture of cement are limestone, clay and gypsum. the main step in the manufacture of cement is the heating of raw meal or slurru in the rotary kiln at a very high temperature `1400-1600^(@)C`. Finally `2% or 3%` gypsum is added.
When cement is mixed with water and left as such for sometime, it becomes a hard mass. This is known as setting of cement. It is believed that varous aluminates and silicates present in the cement form hydrates with water which seperate in the form of gel. the gel formed start losing water partly by evaporation and partly by forming hydrates with unhydrated constituents. this results in the formation of a hard mass.
Gypsum is added to portland cement

Options

A. To fasten the process of setting
B. To slow down the process of setting
C. To improve the colour of the cement
D. All of the above are incorrect

Answer

B

Explanation

it slows down the process of setting.