To determine the aggregate impact value of the given aggregate sample.

AGGREGATE IMPACT VALUE TEST

(AASHTO T-85, ASTM C-127)

OBJECT: TO DETERMINE THE AGGREGATE IMPACT VALUE OF THE GIVEN AGGREGATE SAMPLE

PERFORMANCE OBJECTIVE:

Determine impact resistance of the aggregate.

EQUIPMENT:

• Impact testing machine: The machine consists of a metal base. A detachable cylindrical steel cup with an internal diameter of 10.2cm and a depth of 5cm. A metal hammer of weight between 13.5 to 14Kg, 10cm in diameter and 5cm long. An arrangement for raising the hammer and allowing it to fall freely between vertical guides from a height of 38cm on the test sample in the cup.
  ▪A cylinder having 7.5cm dia and a depth of 5cm for measuring aggregates.
  ▪A tamping rod of circular cross-section, 1cm in diameter and 23 cm long, rounded at one end.
  • BS Sieve size 14mm, 10mm, and 2.36mm
  • Balance, oven, metal tray, and brush.

THEORY:

The property of a material to resist impact is known as toughness. Due to movement of vehicles on the road the aggregates are subjected to impact resulting in their breaking down into smaller pieces. The aggregates should therefore have sufficient toughness to resist their disintegration due to impact. This characteristic is measured by impact value test. The aggregate impact value is a measure of resistance to sudden impact or shock, which may differ from its resistance to gradually applied compressive load.

PROCEDURE:

1. The test sample consists of the aggregates passing 14 mm and retained of 10 mm sieve. Wash the sample and dry at 100° to 110°C for four hours and cool to room temperature.
   

1. Fill the cylindrical measure by the aggregate sample to in three equal layers, each layer being given 15 tamping. Struck off the samples aggregate by tamping rod weigh and record the mass of the sample (W₁).
   

1. Place the impact testing machine with its bottom plate flat on the floor so that hammer guides are vertical, fix the cup firmly in its position on the base of the machine and transfer the entire sample in the cup and compact it 25 times.
   

1. Raise the hammer and allow it to fall freely on the aggregates. The sample is subjected to a total of 15 such blows, each being delivered at an interval of not less than one second.
   

1. Remove the crushed aggregate from the cup and sieve from the 2.36 mm sieve. The fraction passing the sieve is weighed (W₂). The fraction retained on the sieve is also weighed (W₃).
   

OBSERVATION AND CALCULATION:

RESULT:

The mean average impact value (AIV) is _______________%.