Write a few lines about cement.

Explanation

Cement is an important building material
IT is also called portland cement.
cement is obtained a material rich in lime. CaO with other material such as day which contains `Sio_2` along with the oxides of Al,Fe and Mg.
composition of port land cement is CaO- 50-60%
`Sio_2-20-25%`
`Al_2o_2-5-10%`
`Mgo-2-3%`
`Fe_2o_3-1-2%`
and `SO_2- 1-2%`
For a good quality of cement the ratio of `Sio_2` to `Al_2o_3` is between 2.5 and 4 and the ratio of lime (Co) to the total of the oxides of `SiO_2, Al_2O_3 and Fe_2O_3` is as close as Z.
The raw materials used for the manufacture of cement are lime stone and day.
`Clay+lime overset(heat) to cement cli nker`
THis cement clinker mixer with 2-3% wt. of gypsum to form cement.
Important ingradients in portland cement are
`Ca_2SiO_4-26%Ca_3SiO_5-51% and Ca_3Al_2O_6-11%`
Setting of cement:
Cement mixed with water to give a hard mass i.e., setting of cement takes place.
THis is due to the hydration of molecules of the cement.
The purpose of adding gypsum is to slow down the process of setting and to get sufficiently hardness.
Uses:
It is used in concrete and rein forced concrete.
It is used in plastering.
IT is used in construction of bridges, dams and buildings.