Question

The main constituents of cement are:
A. Calcium oxide, silicon dioxide, aluminium oxide
B. Calcium oxide, iron oxide, sulphur dioxide
C. Magnesium oxide, silicon oxide, aluminium oxide
D. None of these

Answer 1

Hint: It is made up by the constituent that is known by the name of quick lime and it is white in colour. Another constituent in cement is produced by Bayer process from its ore bauxite. And the third compound is a major constituent of sand.

Complete step by step answer:
As we all know that cement is a binder, a substance used for construction that sets, hardens, and adheres to other materials to bind them together.
We are here discussing Portland cement which is a type of hydraulic cement. Hydraulic cements set and become adhesive due to a chemical reaction between the dry ingredients and water. Portland cement is manufactured by using three major constituents that are calcium oxide, silicon dioxide, and aluminium oxide.
Portland cement is made up by a mixture of silicates and oxides, the four main mineral phases of the clinker that are used are:
\[{{C}_{3}}S\]: Alite (\[3CaO\cdot Si{{O}_{2}}\]);
\[{{C}_{2}}S\]: Belite (\[2CaO\cdot Si{{O}_{2}}\]);
\[{{C}_{3}}A\]: Tricalcium aluminate (\[3CaO\cdot A{{l}_{2}}{{O}_{3}}\])
\[{{C}_{4}}AF\]: Brownmillerite (\[F{{e}_{2}}{{O}_{3}}\]\[4CaO\cdot A{{l}_{2}}{{O}_{3}}\cdot F{{e}_{2}}{{O}_{3}}\])
In Brownmillerite, we should note that there is a presence of \[F{{e}_{2}}{{O}_{3}}\]. But this is present in very small amounts. Iron oxide quantity in cement ranges from 0.5 to 6%.
So by observing the above composition, we now get to one conclusion that our correct option is OptionA. Cement is made up of calcium oxide, silicon dioxide, aluminium oxide.
Additional properties:
We add silicates in cement because silicates are responsible for the cement's mechanical properties.
All the above materials are mixed and put up in cement kilns. The cement kiln heats all the ingredients to about 1500 degrees Celsius in huge cylindrical steel rotary kilns. Kilns are frequently as much as 12 feet in diameter. As the material moves through the kiln, certain elements are driven off in the form of gases. The remaining elements unite to form a new substance called clinker. Clinker comes out of the kiln as grey balls. After the clinker is cooled, cement plants grind it and mix it with small amounts of gypsum and limestone.
We add gypsum in the cement to slow down the hydration process of cement once it is mixed with water.

Note: Cements are characterized as non-hydraulic or hydraulic. Non Hydraulic Cement is composed of lime, gypsum plaster and oxychloride. Non hydraulic Cement hardens when there is a reaction due to carbonation with the carbon dioxide which is naturally present in the air.
We use gypsum to retard the setting time of cement. It allows a longer working time for mixing, transporting and placing. When we add water to cement aluminates and sulphates react and evolve some heat but gypsum acts as coolant and brings down the heat of hydration. Gypsum cements possess considerably greater strength and hardness when compared to non-gypsum cement. Less water is required in gypsum based cement.