Cement MCQ with answer and solution

Concept

Cement clinker is formed by burning raw materials containing calcareous (calcium) and argillaceous (silica, alumina, iron) materials at high temperatures, resulting in calcium silicates, aluminates, and ferrites.

Step-by-step solution

1. Identify the primary raw materials used in cement manufacturing: limestone (source of lime/calcium) and clay/shale (source of silica, alumina, and iron). 2. During burning in a rotary kiln at 1400°C to 1500°C, these oxides react chemically. 3. The resulting product (clinker) consists majorly of calcium silicates ($C₃S$ and $C₂S$), calcium aluminate ($C₃A$), and calcium aluminoferrite ($C₄AF$).

Explanation

Portland cement clinker is primarily composed of calcium silicates (tricalcium silicate and dicalcium silicate), calcium aluminates (tricalcium aluminate), and calcium aluminoferrite (tetracalcium aluminoferrite), commonly referred to as Bogue's compounds.

Why the other options are wrong

B: Calcium oxides exist as free lime in minor quantities, not as a major compound class along with aluminates and ferrite. C: Calcium carbonates are raw materials (limestone) that decompose during burning, not clinker constituents. D: Calcium nitrates are not constituents of cement clinker.

Shortcut

Remember the primary constituents of cement: Lime, Silica, Alumina, Iron oxide combine to form Calcium silicates, Aluminates, and Ferrite.

Common mistake

Confusing raw materials (calcium carbonates, clay) with the actual major constituents of the final burnt clinker (calcium silicates, aluminates, ferrite).