Fine aggregates are those which are retained on
Correct Answer: D. None of these
📚 Detailed Explanation: Definition of Fine Aggregate by Sieve
This question tests careful reading of the definition. Fine aggregate is defined by the sieve it passes through, not the sieve it is retained on. The standard definition covers a range of particle sizes, not a single sieve.
Why D (None of these) is correct: By IS 383, fine aggregate is material that passes through a 4.75 mm IS sieve. The definition covers particles from 4.75 mm down to 75 µm. If the question had asked “retained on 75 µm sieve,” that would correctly describe the coarsest boundary of the fine aggregate fraction. Saying fine aggregates are “retained on 150 micron, 300 micron, or 600 micron” is incorrect because: (a) material retained on a 600 µm sieve is still fine aggregate (it hasn't exceeded 4.75 mm), and (b) material retained on 150 µm may still be fine aggregate too. None of the three specific sieves given defines the boundary of fine aggregate.
Fine Aggregate Size Range
| Sieve | Classification |
|---|---|
| >4.75 mm | Coarse aggregate (retained on 4.75 mm) |
| 75 µm to 4.75 mm | Fine aggregate (passes 4.75 mm, retained on 75 µm) |
| <75 µm | Silt, clay, or dust of fracture (deleterious) |
Key Concepts for Students
- Fine aggregate is defined by passing 4.75 mm, not by retention on any single small sieve.
- All sieves from 150 µm to 4.75 mm are part of the fineness modulus calculation for fine aggregate.
- The trick in this question is distinguishing between the boundary sieve (4.75 mm pass) and sieves used within the FM calculation.