The phenomenon of increase in the volume of a given mass of sand caused by the films of water pushing the sand particles apart is referred to as:
Correct Answer: C. Bulking
📚 Detailed Explanation: Bulking of Sand
Why C (Bulking) is correct:
Water absorption (A): The water taken into the pores of aggregate particles — not related to volume increase.
Leaching (B): Removal of soluble salts from concrete/soil by water flow — completely different phenomenon.
Bulking (C): Exactly the described phenomenon — thin moisture films create surface tension between particles, holding them apart and increasing apparent volume. This is the correct answer.
Chalking (D): Surface disintegration of concrete producing a powdery dust — a durability defect, not related to sand moisture.
Water absorption (A): The water taken into the pores of aggregate particles — not related to volume increase.
Leaching (B): Removal of soluble salts from concrete/soil by water flow — completely different phenomenon.
Bulking (C): Exactly the described phenomenon — thin moisture films create surface tension between particles, holding them apart and increasing apparent volume. This is the correct answer.
Chalking (D): Surface disintegration of concrete producing a powdery dust — a durability defect, not related to sand moisture.
The Bulking Mechanism
| Moisture State | Bulking | Reason |
|---|---|---|
| Bone dry (0%) | 0% | No water film — particles settle together |
| Slightly moist (2–3%) | 10–20% | Thin film begins to push particles apart |
| Peak (4–6%) | 20–35% | Maximum surface tension → maximum volume |
| Very wet (10%+) | Decreasing | Excess water floods voids; particles settle |
| Saturated (submerged) | ~0% | No surface tension; back to base volume |
- Bulking = volume increase of moist sand due to surface tension of water films between particles.
- Maximum bulking at ~5% moisture content; volume can increase by up to 30–40%.
- Fine sand bulks more than coarse sand (higher surface area = more water-film-per-unit-volume effect).