Which among the following are essential constituents of Portland cemen

Which among the following are essential constituents of Portland cement ?

Sand, lime, clay
Silica, alumina, lime
Silica, lime, graphite powder
Sand, graphene, clay
This question was previously asked in
UPSC NDA-1 – 2024
Portland cement is primarily made from materials containing calcium oxide (lime), silicon dioxide (silica), aluminum oxide (alumina), and iron oxide. The main raw materials are typically limestone (for lime) and clay or shale (for silica, alumina, and iron). These materials are heated in a kiln to produce clinker, which is then ground into fine powder with a small amount of gypsum added. Option B lists Silica, Alumina, and Lime, which are the essential oxide components derived from these raw materials, forming the bulk of the cement clinker.
The major chemical components of Portland cement clinker are tricalcium silicate (alite), dicalcium silicate (belite), tricalcium aluminate (celite), and tetracalcium aluminoferrite (ferrite). These are formed from the reaction of lime (CaO), silica (SiO2), alumina (Al2O3), and iron oxide (Fe2O3) during calcination.
Sand is commonly used as an aggregate in concrete (a mixture of cement, aggregates, and water), but it is not a constituent of cement itself. Graphite powder and graphene are forms of carbon and are not standard components of Portland cement. Clay is a raw material containing silica and alumina, used in cement production, but the essential *constituents* within the clinker are the oxides (silica, alumina, lime, etc.) derived from the raw materials.
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