The aggregate impact value is used for determining the property of aggregate known as
Correct Answer: B. toughness
📚 Detailed Explanation: Aggregate Impact Value and Toughness
In concrete technology, mechanical properties of aggregates are tested by different standard tests, each targeting a specific property. The AIV test (IS 2386 Part IV) is specifically designed to assess the ability of aggregate to resist sudden dynamic loading — this is the engineering definition of toughness.
Why B (toughness) is correct: Toughness is the ability of a material to absorb energy before fracturing. The AIV test drops a hammer of standard weight (13.5 kg) from a height of 380 mm, applying 15 blows to a compacted aggregate sample in a cylinder. The percentage of fines generated (passing 2.36 mm sieve) relative to the original mass is the AIV. A lower AIV = tougher aggregate. This is distinct from: Hardness (resistance to scratching/indentation — measured by LA abrasion), Abrasion resistance (wear from sustained rubbing — also LA abrasion), Specific gravity (mass/volume ratio — immersion test).
Mechanical Test Summary for Coarse Aggregate
| Test | Property Measured | Standard | Acceptance Limit |
|---|---|---|---|
| AIV (Impact Value) | Toughness | IS 2386 Part IV | ≤30% (roads), ≤45% (buildings) |
| ACV (Crushing Value) | Strength / crushing | IS 2386 Part IV | ≤30% (roads), ≤45% (concrete) |
| LA Abrasion | Hardness / abrasion | IS 2386 Part IV | ≤30% (roads), ≤50% (concrete) |
| Specific Gravity | Density / absorption | IS 2386 Part III | 2.6–2.9 typical |
Key Concepts for Students
- AIV = toughness; ACV = crushing strength; LA = hardness/abrasion — remember these three pairings for exam questions.
- The AIV standard apparatus: steel cylinder (102 mm dia, 50 mm depth), 13.5 kg hammer, 380 mm drop, 15 blows.
- For heavy duty floors and runway pavements, AIV must be ≤30%; for normal building concrete, ≤45% is acceptable.