According to IS : 382-1963, a good aggregate should be ………
Correct Answer: D. All options are correct
📚 Detailed Explanation: Requirements for Good Aggregate per IS 382
IS 382 (now largely superseded by IS 383) specified the properties required of aggregates for use in concrete. Good aggregate must satisfy multiple criteria simultaneously, because each property addresses a different mode of potential failure or degradation.
Why D (All options are correct) is correct: A good aggregate must be: (1) Chemically inert — it should not react with cement compounds, atmospheric CO2, moisture, or sulphates. Reactive silica (alkali-silica reaction, ASR) and reactive sulphates both cause destructive expansion. (2) Sufficiently strong — aggregate strength must exceed the design strength of the concrete; weak aggregate fails before the cement matrix. (3) Hard and durable — it must resist abrasion in use and maintain its properties over the structure's design life without degrading.
Properties of Good Aggregate
| Property | Why Required | Test / Limit |
|---|---|---|
| Chemically inert | Prevents ASR expansion, sulphate attack | IS 2386 Part VII (ASR test) |
| Sufficiently strong | Aggregate failure limits concrete strength | ACV ≤30% (IS 2386 Part IV) |
| Hard and durable | Resistance to wear and weathering | LA abrasion ≤30–50% |
Key Concepts for Students
- Alkali-Silica Reaction (ASR) is the most common chemical reaction caused by reactive aggregate; it produces an expansive gel that cracks concrete from within.
- Aggregate strength is not tested directly but inferred from ACV (Aggregate Crushing Value) and AIV (Aggregate Impact Value) tests.
- Clean, hard, strong, well-graded, chemically inert is the classic five-word summary of good aggregate properties.