The bulk density of aggregate is not affected by
Correct Answer: D. size of container used
📚 Detailed Explanation: Bulk Density and Container Size
Bulk density (unit weight) is the mass of aggregate that fills a unit volume container, including both the aggregate particles and the air voids between them. Its value depends on how well the particles pack — which depends on their shape, grading, and degree of compaction. Container size, however, is not a variable that affects the measured value as long as the container meets the minimum size requirement.
Why D (size of container) is correct: IS 2386 (Part III) specifies the minimum container volume based on the maximum aggregate size, to ensure the measurement is representative and edge effects are negligible. As long as the container is at least 5 times the maximum aggregate size, the bulk density measurement is consistent — using a slightly larger or smaller (but still adequate) container does not change the result. Contrast: void content (A), shape (B), and grading (C) all directly change how tightly the particles pack and therefore directly change bulk density.
Factors Affecting vs. Not Affecting Bulk Density
| Factor | Affects Bulk Density? | Reason |
|---|---|---|
| Void content | Yes | More voids = lower mass per unit volume |
| Shape (rounded vs angular) | Yes | Rounded packs denser = higher BD |
| Grading (well-graded) | Yes | Small fill gaps of large = higher BD |
| Container size (adequate) | No | Packing is same regardless of container |
Key Concepts for Students
- Minimum container volume per IS 2386 Part III: for 40 mm MSA, use ≥15-litre container; for 20 mm MSA, ≥3-litre container.
- Typical bulk densities: fine aggregate 1400–1600 kg/m³; coarse aggregate 1400–1700 kg/m³.
- Bulk density is used in mix design to convert volume proportions to mass proportions for batching.