Reviewed by Er. Inderjit Sharma (Retd.), Punjab PWD
What is Aggregate Impact Value (AIV)? It measures how well aggregate resists sudden blows, like the pounding from traffic wheels and rollers. A hammer is dropped on the stone 15 times and we weigh how much of it breaks into fine dust.
Lower AIV = tougher stone. An AIV of 15% means only 15% of the sample was crushed to fines.
This guide follows IS 2386 (Part 4).
The Idea in One Picture
Apparatus Required
Impact testing machine
Hammer of 13.5–14 kg falls 380 mm onto the aggregate in a steel cup.
Cylindrical measure
Fixes the sample size: filled in 3 layers.
Steel cup
Holds the aggregate under the hammer.
Tamping rod
25 strokes per layer with the rounded end.
Sieves 12.5, 10, 2.36 mm
Prepare the 12.5–10 mm sample and separate the fines after the test.
Balance (0.1 g) & oven
Weigh to 0.1 g; dry at 105–110 °C.
The Impact Testing Machine
Procedure
- Sieve the aggregate and take material passing 12.5 mm and retained on 10 mm.
- Dry it in the oven at 105–110 °C for about 4 hours and let it cool.
- Fill the cylindrical measure (75 mm × 50 mm) in 3 equal layers, giving each layer 25 strokes of the rounded end of the rod. Strike off the top level.
- Weigh this aggregate: A. Use the same weight for every test.
- Transfer it into the steel cup of the machine and compact it with 25 strokes of the rod.
- Give it 15 blows of the hammer, each falling freely, at least 1 second apart.
- Take out all the crushed material and sieve it on the 2.36 mm sieve until no more passes. Weigh the part passing (C) and the part retained (B).
- If B + C is less than A by more than 1 g, discard the result and repeat. Do at least two tests.
Calculation
A = weight of the oven-dry sample; C = weight of fines passing the 2.36 mm sieve. Report each result and the mean to two decimal places.
What the Result Means
| AIV | Toughness of the stone |
|---|---|
| Below 10% | Exceptionally strong |
| 10–20% | Strong |
| 20–30% | Satisfactory for road surfacing |
| Above 35% | Weak; not suitable for road surfacing |
Try It: Impact Value Calculator
Enter your weights in grams. The values filled in are a worked example.
Precautions
🏗️ Firm, level base
The machine must rest on a level, rigid floor without packing or wedges, so the guide columns stay vertical.
⬇️ Free fall
Let the hammer fall freely through 380 mm; don’t push or slow it. Keep 1 second between blows.
🧹 Collect all fines
Brush every bit of crushed material out of the cup. Lost fines give a falsely low AIV.
🦺 Safety
Keep hands clear of the cup when lifting and releasing the hammer; wear safety shoes and goggles.
Practical Tips for Site Engineers
1. Typical Maximum AIV
| Use | Maximum AIV |
|---|---|
| Concrete for wearing surfaces (floors, pavements) | 30% (IS 383) |
| Other concrete | 45% (IS 383) |
| Wet Mix Macadam (WMM) | 30% (MoRTH) |
| Dense Bituminous Macadam (DBM) | 27% (MoRTH) |
| Bituminous Concrete (BC) | 24% (MoRTH) |
Always follow your contract specification.
2. Good Site Habits
- Approve the quarry first: test AIV (with abrasion, shape and absorption) before accepting a new source, then at the frequency in your specification.
- Quick and portable: the impact test needs a small sample and a simple machine, so it’s ideal for a site lab, unlike the bigger crushing value test.
- Watch for weak or weathered stone: soft, discoloured or earthy pieces, or stone that breaks easily with a hammer, usually gives high AIV.
- Wet AIV for doubtful stone: some stone gets weaker when wet. Where specified, test soaked samples too.
- Look at the road: stone that crushes under the roller (lots of dust, rounded edges) is a warning sign; test it.
- Keep records of source, date, quantity represented and result with the delivery register.
Key Takeaways
- AIV shows resistance to sudden blows; lower is tougher.
- Sample 12.5–10 mm, oven-dried; fill the 75 × 50 mm measure in 3 layers × 25 strokes (A).
- 15 blows of a 13.5–14 kg hammer falling 380 mm; sieve on 2.36 mm (C).
- AIV = C ÷ A × 100; repeat if B + C is more than 1 g short of A.
- On site: typical limits are 30% for wearing surfaces and WMM, 27% for DBM, 24% for BC, and 45% for other concrete.
References: IS 2386 (Part 4): Methods of Test for Aggregates – Mechanical Properties; IS 383:2016: Coarse and Fine Aggregate for Concrete; MoRTH Specifications for Road and Bridge Works (Tables 400-12, 500-8, 500-16).