The minimum percentage of chemical ingredient of cement is that of ..........
Try it first: pick an option, then read the explanation.
The Main Ingredients of Portland Cement
Portland cement is not a single chemical, but a complex mixture of several oxides. The proportions of these oxides are carefully controlled to achieve the desired properties. The four major oxides are Lime, Silica, Alumina, and Iron Oxide. Other minor oxides, like Magnesium Oxide, are also present and play a role.
Detailed Analysis of Percentages
(a) magnesium oxide (MgO)
This is the correct answer. Magnesium oxide is typically present in the smallest quantity among the options listed, usually ranging from 0.1% to 4%. While it contributes to hardness and color, its amount is strictly limited because excess magnesia can cause unsoundness (delayed expansion) in the hardened concrete.
(b) Iron oxide (Fe₂O₃)
Iron oxide is present in a range of about 0.5% to 6%. It acts as a flux during manufacturing and gives cement its characteristic greyish color. Its typical percentage is higher than that of magnesium oxide.
(c) alumina (Al₂O₃)
Alumina is a major component, typically present from 3% to 8%. It is responsible for quick setting and lowering the clinkering temperature.
(d) lime (CaO)
Lime is the most abundant ingredient in cement, making up 60% to 67% of the total. It is the primary binding component and is responsible for strength. It has the highest percentage, not the minimum.
Typical Composition of Ordinary Portland Cement
| Chemical Ingredient | Oxide Formula | Approximate Percentage |
|---|---|---|
| Lime | CaO | 60 - 67% |
| Silica | SiO₂ | 17 - 25% |
| Alumina | Al₂O₃ | 3 - 8% |
| Iron Oxide | Fe₂O₃ | 0.5 - 6% |
| Magnesium Oxide | MgO | 0.1 - 4% |
Study Tips
- Lime is #1: Always remember that Lime (CaO) is the most plentiful ingredient in cement.
- Order of Magnitude: Try to remember the general order of abundance: Lime > Silica > Alumina > Iron Oxide > Magnesium Oxide.
- Minor but Mighty: Even though ingredients like MgO are present in small quantities, they have a significant impact. Excess MgO can be very harmful, which is why its content is strictly controlled.