Aggregate Impact Value Test as per IS: 2386 (Part IV)- 1963

Introduction: The impact test is conducted to determine the aggregate impact value (AIV) of the given sample of coarse aggregate. The aggregate impact value indicates the resistance of the aggregates to impact. This test is conducted as per the Indian Standard Specification IS: 2386 (Part IV)- 1963.

Apparatus:

1. Impact testing machine
2. Cylindrical measure of 75 mm diameter and 50 mm depth
3. Tamping rod of circular cross-section of 10 mm diameter and 230 mm length, rounded at one end
4. Balance of accuracy 1 g
5. IS sieves of sizes 12.5 mm, 10 mm and 2.36 mm
6. Oven

 

Procedure:

1. The test sample of coarse aggregate shall be sieved through 12.5 mm IS sieve and retained on 10 mm IS sieve.
2. The aggregate sample shall be dried in an oven at a temperature of 100°C to 110°C for four hours and cooled to room temperature.
3. The cylindrical measure shall be filled with the prepared aggregate sample in three layers, each layer being tamped with 25 strokes of the tamping rod.
4. The surplus aggregate shall be struck off using a tamping rod as a straightedge.
5. The impact testing machine shall be placed on a level and plane concrete floor, which is free from vibrations. The machine shall be held firmly to prevent any undue vibration during testing.
6. The test sample and the cylindrical measure shall be placed in the machine and the hammer shall be raised to a height of 380 mm above the upper surface of the aggregate sample.
7. The machine shall be allowed to fall freely on the aggregate sample. The number of blows delivered to the sample shall be 15.
8. The crushed aggregate shall then be sieved through 2.36 mm IS sieve and the fraction passing through the sieve shall be weighed to an accuracy of 1 g. This fraction is the AIV.

Observations and Calculations:

Weight of dry sample = _________ g 

Weight of aggregate passing through 2.36 mm IS sieve after impact = _________ g 

Aggregate Impact Value (AIV) = (Weight of aggregate passing through 2.36 mm IS sieve / Weight of dry sample) x 100

Results:

The Aggregate Impact Value of the given sample of coarse aggregate is __________%.

Precautions:

1. The testing machine should be placed on a level and plane concrete floor, which is free from vibrations.
2. The test sample should be dried in an oven at a temperature of 100°C to 110°C for four hours and cooled to room temperature before conducting the test.
3. The tamping of each layer of aggregate sample should be done with 25 strokes of the tamping rod.
4. The number of blows delivered to the sample should be exactly 15.
5. The sieves used for sieving the crushed aggregate should be of IS specification and should be checked for their accuracy before conducting the test.

Conclusion: The Aggregate Impact Value of the given sample of coarse aggregate is __________%. This value indicates the resistance of the aggregate to impact. A higher value of AIV indicates that the aggregate is stronger and more resistant to impact. The test helps in determining the suitability of the aggregate for use in construction work.

 

Limiting Values:

 The following are the limiting values for impact value for aggregates for pavement layers:

1. For bituminous macadam: The maximum allowable impact value is 30%.

2. For Water bound macadam (WBM) and wet mix macadam (WMM): The maximum allowable impact value is 40%.

3. For pre-coated aggregate: The maximum allowable impact value is 30%.

4. For cement concrete road: The maximum allowable impact value is 45%.

The limiting values for the impact value of aggregates for pavement layers are specified in the respective codes of practice and specifications for construction work. These values ensure that the aggregates used in the pavement layers have sufficient strength and durability to withstand the traffic loads and other environmental factors. It is important to ensure that the aggregates used in pavement layers meet the specified impact value limits to ensure the long-term performance of the pavement.