SSC JE Civil Engineering 23-Mar-2021 Shift 1 Paper

Question : 120 of 200

Marks: +1, -0

What is the approximate composition of silicon dioxide (SiO2) present in ordinary Portland cement?

Solution:

Concept:
The following table shows the composition of cement and its properties.

Ingredients	Within limit	If in excess
Lime (62 – 65%)	Controls strength and soundness	Makes the cement unsound and it expands and disintegrates
Silica (17 - 25 %)	Adds strength to cement, as it forms $\C_2\S$ and $\C_3\S$	Causes slow setting of cement
Alumina (3 - 8 %)	Provides quick setting of cement and lowers the clinkering temp	Lowers the strength
Iron oxide (3 - 4 %)	Provides color, hardness, strength and helps infusion of raw material
Magnesia (1 - 3 %)	Provides hardness and color Decreases shrinkage	Makes the cement unsound
Alkalies(0.2 - 1 %)	Should be in limit	Alkali aggregate reactionEfflorescence and staining

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