Question

Except for lime, a major constituent of Portland cement is
A. Silica
B. Alumina
C. Iron oxide
D. Magnesia

Answer 1

Hint: Cement is a significant material used for establishing buildings. It was initially introduced in England in 1824 by Joseph Aspdin. It is also called Portland cement as it matches the natural limestone quarried in the Isle of Portland, England. This Portland cement when mixed with another constituent becomes ready for use in construction.

Complete Step by Step Answer:
Cement is a commodity formed by blending a material abundant in lime, CaO, with other materials like clay which comprises silica, and silicon dioxide along with the oxides of aluminium, iron, and magnesium.

The regular composition of Portland cement is:
- Calcium oxide or CaO-\[{\rm{50 - 60\% }}\],
- Silicon dioxide -\[{\rm{Si}}{{\rm{O}}_2}{\rm{ - 20 - 25\% }}\],
- Alumina or \[{\rm{A}}{{\rm{l}}_{\rm{2}}}{{\rm{O}}_{\rm{3}}}{\rm{ - 5 - 10\% }}\],
- Magnesium oxide or MgO-\[{\rm{2 - 3\% }}\],
- Ferric oxide or \[{\rm{F}}{{\rm{e}}_{\rm{2}}}{{\rm{O}}_{\rm{3}}}{\rm{ - 1 - 2\% }}\] and
- Sulphur trioxide or \[{\rm{S}}{{\rm{O}}_{\rm{3}}}{\rm{ - 1 - 2\% }}\].

For a decent quality cement, the ratio of silica to alumina (\[{\rm{A}}{{\rm{l}}_{\rm{2}}}{{\rm{O}}_{\rm{3}}}\]) must be within 2.5 and 4 and the ratio of lime (CaO) to the aggregate of the oxides of silicon (\[{\rm{Si}}{{\rm{O}}_2}\]) aluminium (\[{\rm{A}}{{\rm{l}}_{\rm{2}}}{{\rm{O}}_{\rm{3}}}\]) and iron (\[{\rm{F}}{{\rm{e}}_{\rm{2}}}{{\rm{O}}_{\rm{3}}}\]) should be around 2.
The raw materials for the manufacturing of cement are limestone and clay.
So, option A is correct.

Additional Information: When blended with water, the setting of cement occurs to provide a hard mass. This is because of the hydration of the molecules of the constituents and their rearrangement. The objective of adding gypsum is just to slow down the method of setting the cement so that it is adequately solidified.

Note: Cement has evolved to be a product of national requirements for any country after iron and steel. It is utilised in concrete and reinforced concrete, in plastering and the building of bridges, dams and buildings.