The bulk density of aggregates depends upon its :
Correct Answer: D. All option are correct
📚 Detailed Explanation: Factors Affecting Bulk Density of Aggregates
Bulk density (unit weight) is the mass of aggregate required to fill a unit volume, including the air voids between particles. It is not an intrinsic material property like specific gravity — it depends on how the particles pack, which in turn depends on multiple factors.
Why D (All option are correct) is correct: (1) Shape — rounded particles pack more closely (less voids) than angular ones, giving higher bulk density for the same specific gravity. (2) Grading — well-graded aggregate (many sizes) packs more densely than single-size aggregate because smaller particles fill the voids between larger ones, increasing bulk density. (3) Compaction — the same aggregate will have a higher bulk density when rodded/vibrated (compacted) than when loosely poured; IS 2386 (Part III) measures both.
Effect of Each Factor on Bulk Density
| Factor | Effect on Bulk Density |
|---|---|
| Shape (rounded vs angular) | Rounded: higher BD; Angular: lower BD (more voids) |
| Grading (well-graded vs single-size) | Well-graded: higher BD; Single-size: lower BD |
| Compaction (loose vs compacted) | Compacted: higher BD; Loose: lower BD |
Key Concepts for Students
- IS 2386 (Part III) measures both loose bulk density and compacted bulk density; the latter is used in concrete mix design volume calculations.
- Bulk density does NOT depend on the size of the test container (for a sufficiently large container relative to aggregate size).
- Typical coarse aggregate bulk density: 1400–1700 kg/m³; fine aggregate: 1400–1600 kg/m³.