The coarsest sand is available in zone
Correct Answer: A. Zone I
📚 Detailed Explanation: IS 383 Grading Zones for Fine Aggregate
IS 383 (Specification for Coarse and Fine Aggregates for Concrete) classifies fine aggregate into four grading zones based on the percentage passing on a set of sieves. These zones range from coarse (Zone I) to very fine (Zone IV).
Why A (Zone I) is correct: Zone I has the highest percentage retained on each sieve (i.e., fewer fines pass), meaning the particles are generally larger — coarser sand. Zone IV has the lowest percentages retained (more fines pass) — this is the finest sand. The progression from coarse to fine is Zone I (coarsest) → Zone II → Zone III → Zone IV (finest).
IS 383 Grading Zones Summary
| Zone | Sand Type | Preferred Use | FM Range |
|---|---|---|---|
| Zone I | Coarsest | Mass concrete, floors | ~3.5–4.0 |
| Zone II | Medium-coarse | General structural concrete (preferred) | ~2.9–3.5 |
| Zone III | Medium-fine | Plastering, thin sections | ~2.3–3.0 |
| Zone IV | Finest | Avoid in concrete if possible | ~1.5–2.3 |
Key Concepts for Students
- Zone I = coarsest, Zone IV = finest — the number goes up as the sand gets finer.
- Zone II sand is ideal for most structural concrete mixes as it gives good workability and strength.
- Zone IV sand needs additional water for the same workability, increasing the w/c ratio and reducing strength.