The raw materials used for the manufacture of Portland cement are

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Lime, silica and sulphur dioxide

Lime, silica and carbon dioxide

Lime, silica and alumina

Lime, silica and boric acid

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UPSC NDA-2 – 2019

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The primary raw materials used for the manufacture of Portland cement clinker are calcium oxide (usually derived from limestone or chalk), silicon dioxide (silica, typically from clay or sand), and aluminium oxide (alumina, from clay or bauxite). These materials are mixed in specific proportions, heated in a kiln to high temperatures (calcination and clinkering), and then ground to produce cement. Option C lists lime, silica, and alumina, which are the essential components derived from these raw materials.

– The main chemical components of Portland cement are calcium silicates, calcium aluminates, and calcium ferroaluminates.
– These compounds are formed by heating a mixture of calcareous material (like limestone, source of CaO) and argillaceous material (like clay, source of SiO2 and Al2O3) in a kiln.
– Minor components like iron oxide and gypsum (added during grinding) are also involved but lime, silica, and alumina are the core raw material oxides.

– Limestone (CaCO3) is heated to produce lime (CaO) and carbon dioxide (CO2).
– Clay provides silica (SiO2), alumina (Al2O3), and iron(III) oxide (Fe2O3).
– Sulphur dioxide and boric acid are not standard raw materials for Portland cement. Carbon dioxide is a byproduct of the calcination process, not a raw material that is added.

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