As per IS 383 (1970), the passing percentage of fine aggregates under Zone IV from an IS 600 microns sieve is
Correct Answer: D. 80 – 100%
🧱 Detailed Explanation: Zone IV Fine Aggregate Grading at 600 μm (IS 383:1970)
Zone IV represents the finest gradation of fine aggregates under IS 383:1970. Very fine sands (Zone IV) have a large specific surface area per unit mass, which means they require more cement paste for adequate coating and tend to produce mixes with higher water demand — potentially weakening concrete if the water-cement ratio is not carefully controlled.
Why D (80–100%) is correct for Zone IV at 600 μm:
Zone IV is the finest zone — most of its particles are smaller than 600 μm (0.6 mm). Therefore, when you sieve Zone IV sand through a 600 μm IS sieve, 80 to 100% of the material must pass. This very high passing percentage directly distinguishes Zone IV from coarser zones.
Zone IV is the finest zone — most of its particles are smaller than 600 μm (0.6 mm). Therefore, when you sieve Zone IV sand through a 600 μm IS sieve, 80 to 100% of the material must pass. This very high passing percentage directly distinguishes Zone IV from coarser zones.
The wrong options correspond to coarser zones at 600 μm:
• A (15–34%) = Zone I at 600 μm (coarsest zone — most particles retained here)
• B (8–30%) = Zone II at 300 μm (different sieve)
• C (60–79%) = Zone III at 600 μm
IS 383:1970 — % Passing at 600 μm Sieve (All Zones)
| Zone | % Passing 600 μm | Character |
|---|---|---|
| Zone I | 15–34 | Coarsest — most retained at 600 μm |
| Zone II | 35–59 | Medium coarse |
| Zone III | 60–79 | Medium fine |
| Zone IV | 80–100 | Finest — almost all passes 600 μm |
Zone IV Fine Aggregate — Full Grading Limits
| IS Sieve | Zone IV % Passing |
|---|---|
| 10 mm / 4.75 mm | 100 / 95–100 |
| 2.36 mm / 1.18 mm | 95–100 / 90–100 |
| 600 μm | 80–100 |
| 300 μm / 150 μm | 15–50 / 0–15 |
Key Concepts for Students
- The 600 μm sieve is the best discriminator between IS 383 zones: 15–34% (I) / 35–59% (II) / 60–79% (III) / 80–100% (IV). Memorise this column.
- Zone IV sand has high surface area → higher water and cement demand. IS 383 recommends using it only when coarser zones are unavailable, and with adjusted mix proportions.
- Using Zone IV sand without increasing cement or reducing fine-aggregate proportion results in a harsh, bleed-prone, potentially weak concrete.
- Fineness modulus of Zone IV sand typically falls in the range of 1.5–2.2, well below the recommended 2.6–2.9 for most structural concrete — another signal that mix adjustment is needed.