The bulk density of aggregates is generally expressed as :
Try it first: pick an option, then read the explanation.
Correct answer: C. kg/litre
Detailed Explanation: Units of Bulk Density for Aggregates
Bulk density is the mass of a unit volume of aggregate, including the air voids between particles. It is determined by the IS 2386 (Part III) container test: a standard container of known volume is filled with aggregate (in a standard manner) and weighed. Dividing mass by volume gives bulk density.
Why C (kg/litre) is correct: In the IS 2386 (Part III) test, the container volume is measured in litres and mass in kilograms, so bulk density is naturally expressed in kg/litre. This is numerically convenient: water = 1.0 kg/litre (the reference density), and typical aggregate bulk density is 1.4–1.7 kg/litre. While kg/m³ is also technically correct and equivalent (1 kg/litre = 1000 kg/m³), the standard test method and examination literature conventionally use kg/litre for aggregate bulk density.Bulk Density Reference Values
| Material | Bulk Density (kg/litre) |
|---|---|
| Water | 1.0 |
| Fine aggregate (loose) | 1.4–1.6 |
| Coarse aggregate (loose) | 1.4–1.7 |
| Coarse aggregate (compacted) | 1.5–1.8 |
Key Concepts for Students
- Bulk density < Specific Gravity because bulk density includes inter-particle air voids; specific gravity is the density of the solid aggregate particle itself.
- The IS 2386 test uses a standard cylinder (3 litre or 15 litre depending on aggregate size) filled in three layers with 25 tamping strokes per layer for the compacted test.
- Angularity number is calculated from bulk density: it is the void percentage in excess of 33% for a sample compared to a standard rounded aggregate.