Concept: Aggregate Impact Test: It is conducted to determine the toughness of the aggregates. For testing, the specimen passing through 12.5 mm sieve but retained on 10 mm sieve is filled in 3 layers with 25 time stamping on each layer and then hammer of 13.5 to 14 kg is dropped freely from a height of 38 cm for 15 blows. Aggregate impact value is then the percentage of fine passing through 2.36 mm sieve to total aggregate weight. Aggregate impact value for different requirement are as follows:
Type of pavement Material/Layer
Maximum aggregate impact value (%)
WBM Sub base course
50
Cement Concrete Base course
45
Bituminous Macadam, Base course
35
WBM Surface Course
30
Bituminous wearing surfaces
30
∴ For concreting the surface of the runways, roads and pavements, the aggregate impact value shall not exceed by weight 0.3 and 0.5 for WBM.