Specific gravity of OPC is generally:
⚖️ What is Specific Gravity?
Specific gravity is a measure of density. It is the ratio of the density of a substance to the density of a reference substance, which is usually water. A specific gravity of 3.15 means that cement is 3.15 times denser than water.
For cement, specific gravity is an important indicator of its quality. A lower-than-normal value can indicate that the cement is old, has absorbed moisture from the air (pre-hydration), or has been adulterated with lighter materials. This test is typically performed using a Le Chatelier flask.
📝 Detailed Analysis of the Options
(a) 4.92
This value is extremely high. A material with this specific gravity would be significantly denser than most common construction materials, approaching the density of some metals. It is not a realistic value for cement.
(c) 2.10 & (d) 1.75
These values are too low for good quality cement. They are closer to the specific gravity of materials like coal or some types of stone aggregate. A cement with such a low specific gravity would likely be heavily adulterated or severely affected by moisture.
(b) 3.15
This is the correct answer. The specific gravity of Ordinary Portland Cement (OPC) is standardized and generally falls within a very narrow range, with 3.15 being the accepted standard value. Most fresh, high-quality OPC will have a specific gravity between 3.10 and 3.16. This high density reflects the nature of the finely ground clinker from which it is made.
📊 Specific Gravity of Common Materials
| Material | Typical Specific Gravity |
|---|---|
| Ordinary Portland Cement | 3.15 |
| Sand / Aggregate | 2.6 - 2.8 |
| Water | 1.0 |
| Steel | 7.85 |
💡 Study Tips
- Memorize 3.15: The specific gravity of OPC is a fundamental value in civil engineering. You should commit the number 3.15 to memory.
- Higher is Denser: Understand that specific gravity is a measure of density. Cement is a dense powder, much denser than water (1.0) and slightly denser than typical rock/sand (2.6-2.8).
- Low Value = Bad Cement: A key application of this property is quality control. If a lab test shows a specific gravity significantly below 3.10, it's a red flag that the cement may be old, wet, or impure.