Portland cement contains '$\mathrm{X}$' to enhance the setting time. What is '$\mathrm{X}$'?

Cement is an important building material. It was first introduced in England in 1824 by Joseph Aspdin. It is also called Portland cement because it resembles with the natural limestone quarried in the Isle of Portland, England.

The raw materials for the manufacture of cement are limestone and clay.

When mixed with water, the setting of cement takes place to give a hard mass. This is due to the hydration of the molecules of the constituents and their rearrangement. The purpose of adding gypsum is only to slow down the process of setting of the cement so that it gets sufficiently hardened.

Hence,Gypsum$\left({\mathrm{CaSO}}_4·2{\mathrm{H}}_2\mathrm{O}\right)$ is used to enhance setting time in portland cement.