Aggregate impact value test

The aggregate impact value (AIV) measures the resistance of an aggregate to sudden shock or impact (toughness). It is the percentage of fines (passing 2.36 mm) produced when the sample is subjected to 15 blows of a standard hammer (IS:2386 Part IV).

Apparatus

• Impact testing machine: a metal base, a steel cup (102 mm inside diameter, 50 mm deep), and a hammer of 13.5-14 kg (usually 14 kg) with a free fall of 380 mm.
• Cylindrical measure (75 mm diameter, 50 mm deep), tamping rod (10 mm diameter, 230 mm long), IS sieves 12.5, 10 and 2.36 mm, balance.

        | hammer 14 kg
        |  falls 380 mm
     ___v___
    |  cup  |  <- aggregate in 1 layer 
    |_______|
      base

Procedure

1. Take dry aggregate passing the 12.5 mm and retained on the 10 mm sieve (about 300-400 g, enough to fill the measure in three layers).
2. Fill the cylindrical measure in three layers, tamping each layer with 25 strokes; weigh the sample ($W_1$).
3. Transfer it to the cup of the machine (fixed on the base) in a single layer and tamp it 25 times.
4. Raise the hammer to 380 mm and let it fall freely; give 15 blows, each at an interval of not less than 1 second.
5. Remove the crushed material and sieve it through the 2.36 mm sieve. Weigh the passing portion ($W_2$) and the retained portion ($W_3$); $W_2 + W_3$ should not differ from $W_1$ by more than 1 g.

$$\text{AIV} = \frac{W_2}{W_1} \times 100\%$$

Report the mean of two tests.

Interpretation

• Below 10%: exceptionally strong; 10-20%: strong; 20-30%: satisfactory for road surfacing; above 35%: weak.
• Limits (IRC/NRS 2070): not more than 30% for the wearing course and not more than 35-45% for bituminous base and WBM.