Aggregate Impact Value (AIV):
Resistance of aggregate to sudden shock or impact is known as toughness of aggregate. Aggregate impact value (AIV) is a relative measure of toughness of aggregate. To determine the aggregate crushing value, a sample of aggregate passing by 12.5 mm and retained on 10 mm is taken. This sample of aggregate is dried for 4 hrs in oven at 100-110oC. After getting the dried sample cooled, it is filled in the cylindrical container in three layers by tamping each layer 25 times with tamping rod in standard manner and the weight of sample 'A' is taken. This aggregate sample (weighing 'A') is placed in the impact load machine in which the impact load is applied through 15 blows of standard hammers falling from a height of 380 mm. The aggregate is then taken out and sieved by 2.36 mm sieve. The weight 'B' of the fraction passing by 2.36 mm is taken.
Aggregate impact value is determined within percentage through:
AIV = B/A × 100
where, A = Weight of prepared aggregate sample, and
B = Weight of aggregate passing through 2.36 mm after applying the load.
The AIV should not be more than 45% for the concrete used for other than wearing surface, whereas AIV should be limited to 30% for the concrete used for wearing surface such as roads, runways and air field pavements.