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Ingredients of cement and functions
Short answer
Lime (CaO, 60–67%) gives strength, excess unsoundness. Silica (SiO₂, 17–25%) gives strength, excess slows set. Alumina (Al₂O₃, 3–8%) quickens setting, flux. Iron oxide (0.5–6%) gives colour, flux. Magnesia (0.1–4%) adds hardness, excess unsoundness. Gypsum (2–3%) controls setting time.
What are the ingredients of (Portland) cement? Explain their functions.
Portland cement is made from raw materials rich in lime, silica, alumina and iron. After burning, the ingredients in cement are:
| Ingredient | Percentage | Function |
|---|---|---|
| Lime (CaO) | 60-67 | Main constituent; controls strength and soundness. Excess causes expansion and unsoundness; less lowers strength and speeds setting |
| Silica (SiO₂) | 17-25 | Gives strength through calcium silicates. Excess slows setting |
| Alumina (Al₂O₃) | 3-8 | Quick setting; acts as flux. Excess lowers strength |
| Iron oxide (Fe₂O₃) | 0.5-6 | Gives colour and acts as flux, helps in fusion |
| Magnesia (MgO) | 0.1-4 | Gives hardness and colour; excess causes unsoundness |
| Sulphur trioxide (SO₃) | 1-3 | Makes cement sound; excess unsoundness |
| Calcium sulphate (gypsum) | 2-3 | Added during grinding to control setting time |
| Alkalies (Na₂O, K₂O) | 0.4-1.3 | Excess causes efflorescence and alkali–aggregate reaction |
✓ Answer checked by Claude Opus 5.5 (high effort)
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