AGGREGATE IMPACT VALUE TEST IS: 2386 (Part IV)
OBJECTIVE:
To determine the impact value of the road aggregates.
To assess their suitability in road construction on the basis of impact value.
APPARATUS/EQUIPMENTS REQUIRED:
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.
In other words, Resistance of the aggregates to impact is termed as toughness. Aggregates used in the pavement should be able to resist the effect caused by the jumping of the steel tyred wheels from one particle to another at different levels causes severe impact on the aggregates.
PROCEDURE:
Place the plunger centrally so that it falls directly on the aggregate sample and does not touch the walls of the cylinder in order o ensure that the entire load is transmitted on o the aggregates.
In the operation of sieving the aggregates through 2.36 mm sieve the sum of weights of fractions retained and passing the sieve should not differ from the original weight of the specimen by more than 1 gm.
The tamping is to be done properly by gently dropping the tamping rod and not by hammering action. Also the tamping should be uniform over the surface of the aggregate taking care that the tamping rod does not frequently strike against the walls of the mould.
Detailed procedure along with calculations is attached below.
OBJECTIVE:
To determine the impact value of the road aggregates.
To assess their suitability in road construction on the basis of impact value.
APPARATUS/EQUIPMENTS REQUIRED:
- Impact testing machine weighing 45 to 60 kg and having a metal base plate with a plane lower surface of not less than 30 cm in diameter.
- A cylindrical steel cup of internal diameter 102 mm, depth 50 mm and minimum thickness 6.3 mm.
- A metal hammer or tup weighing 13.5 to 14 kg the lower end is cylindrical in shape, is 50 mm long, 100.0 mm in diameter, with a 2 mm chamber at the lower edge and case hardened. The hammer should slide freely between vertical guides and be concentric with the cup. The free fall of the hammer should be within 380±5 mm.
- A cylindrical metal measure having internal diameter 75 mm and depth 50 mm for measuring aggregates.
- Tamping rod 10 mm in diameter and 230 mm long, rounded at one end.
- Sieve 12.5, 10, and 2.36 mm.
- Balance of capacity 500 g x 0.1 g
- Oven (thermostatically)
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.
In other words, Resistance of the aggregates to impact is termed as toughness. Aggregates used in the pavement should be able to resist the effect caused by the jumping of the steel tyred wheels from one particle to another at different levels causes severe impact on the aggregates.
PROCEDURE:
- Oven dried aggregate specimen passing 12.5 mm sieve and retained on 10 mm sieve is filled in measuring cup in three equal layers by 25 blows with the help of tamping rod and weighed.
- The sample is now transferred to the cup of the impact test apparatus and compacted by tamping rod 25 times again in 3 equal layers.
- Now the hammer is raised to a height of 38 (±0.5) cm above the surface of the aggregate in the cup and is allowed to fall freely in the specimen. In this 15 blows are given to the aggregate specimen at an interval of not less than one second between successive falls.
- Now the tested aggregate sample is sieved through 2.36 mm I.S. Sieve and the fraction passing or retained through this sieve is weighed.
Place the plunger centrally so that it falls directly on the aggregate sample and does not touch the walls of the cylinder in order o ensure that the entire load is transmitted on o the aggregates.
In the operation of sieving the aggregates through 2.36 mm sieve the sum of weights of fractions retained and passing the sieve should not differ from the original weight of the specimen by more than 1 gm.
The tamping is to be done properly by gently dropping the tamping rod and not by hammering action. Also the tamping should be uniform over the surface of the aggregate taking care that the tamping rod does not frequently strike against the walls of the mould.
Detailed procedure along with calculations is attached below.
