Correct Answer - Option 2 : 30% by weight
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.