The specific gravity of cement is generally about:
🔬 Understanding Specific Gravity
Specific Gravity is a measure of density. It is defined as the ratio of the density of a substance to the density of a reference substance, which is usually water at 4°C. For cement, it represents how much denser the cement particles are compared to water. A specific gravity of 3.15 means that cement is 3.15 times denser than water. This value is an important indicator of the quality of cement and is used in concrete mix design calculations. A lower-than-normal value can indicate that the cement is old, has absorbed moisture, or is adulterated.
📝 Detailed Analysis of the Values
(d) 3.15
This is the correct answer. The standard value for the specific gravity of Ordinary Portland Cement is generally taken as 3.15. This value is determined experimentally using a Le-Chatelier flask and a liquid like kerosene, which does not react with cement. This is a standard value that every civil engineer should know.
(a) 2.6 and (b) 2.7
These are incorrect. These values are in the typical range for the specific gravity of natural aggregates like sand and gravel (usually 2.6 to 2.8). They are significantly lower than the specific gravity of cement.
(c) 7.85
This is incorrect. This is the specific gravity of steel, which is used as reinforcement in concrete. It is much denser than cement.
📊 Summary: Specific Gravity of Common Materials
| Material | Typical Specific Gravity |
|---|---|
| Cement | 3.15 |
| Water | 1.0 |
| Sand / Gravel (Aggregates) | 2.6 - 2.8 |
| Steel | 7.85 |
| Wood | ~1.54 (for dense wood) |
| Mercury | 13.6 |
💡 Study Tips
- Memorize the Key Value: The specific gravity of cement, 3.15, is a fundamental constant in civil engineering and frequently appears in exams. Commit it to memory.
- Associate with Other Materials: To avoid confusion, remember the approximate values for other common materials: Aggregates (~2.7), Steel (~7.85), and Water (1). This helps put the value for cement in context.
- Link to the Test Method: Remember that the specific gravity of cement is determined using a Le-Chatelier flask. Don't confuse this with the Le-Chatelier apparatus for soundness.