What will be the percentage of passing aggregate for the grading zone 1 of sieve size 1.18 mm?
Correct Answer: D. 30% – 70%
📚 Detailed Explanation: IS 383:1970 Zone I Grading — 1.18 mm Sieve
IS 383:1970 specifies grading limits for fine aggregates across four zones at six standard sieve sizes: 4.75 mm, 2.36 mm, 1.18 mm, 600 µm, 300 µm, and 150 µm. Zone I represents the coarsest permissible grading of fine aggregate. Knowing these limits is essential for mix design and aggregate acceptance testing.
Why D (30%–70%) is correct: For Zone I at the 1.18 mm sieve, IS 383:1970 specifies that 30%–70% of the sand must pass. This wide band reflects the fact that Zone I sand is relatively coarse — a large proportion of the material is retained above 1.18 mm. The 100% option is impossible for Zone I at 1.18 mm (that would be the 4.75 mm sieve where all FA passes).
IS 383:1970 Grading Limits for Zone I (% Passing)
| Sieve Size | Zone I (% Passing) |
|---|---|
| 4.75 mm | 90–100 |
| 2.36 mm | 60–95 |
| 1.18 mm | 30–70 |
| 600 µm | 15–34 |
| 300 µm | 5–20 |
| 150 µm | 0–10 |
Key Concepts for Students
- Zone I — coarsest: lower passing % at each sieve compared to Zones II, III, IV.
- The 30–70% range at 1.18 mm is a frequently tested value — memorise the complete Zone I column.
- Compare: Zone IV at 1.18 mm allows 90–100% passing, confirming it is a much finer sand.