Transportation Engineering Laboratory, IITG

Transportation Engineering Laboratory, IITGAggregate Impact TestEXPERIMENT NO. NAME OF THE EXPERIMENT: AGGREGATE IMPACT TESTAIM OF THE EXPERIMENT: To determine the aggregate impact value of the given specimen of coarse aggregate.TEST DESCRIPTION:The aggregate impact value of coarse aggregate provides a relative measure of the resistance of an aggregate to sudden shock or impact. The oven dried and accurately weighed aggregates are subjected to a total of 15 blows of specified weight and fall and percentage of fines (finer than 2.36 mm) formed in terms of the total weight of the sample is expressed as the aggregate impact value.APPARATUS USED:1. An aggregate impact testing machine with as per IS: 2386 Part-IV - 1963. The machine shall have a metal base weighing between 22 and 30 kg with a plane lower surface of not less than 30 cm diameter.

Fig.1 Aggregate Impact Testing Machine sketch2. A cylindrical steel cup of internal dimensions:Diameter: 102 mmDepth: 50 mm3. A metal hammer weighing 13.5 to 14 kg, the lower end being cylindrical, 100 cm in diameter and 5 cm long with a 2 mm chamfer at the lower edge.4. Means for raising the hammer and allowing it to fall freely from a height of 380 mm.5. Sieves: The IS Sieves of sizes 12.5, 10 and 2.36 mm.6. A cylindrical metal measure, tared to the nearest gram and of the following dimensions-Diameter: 75 mmDepth: 50 mm7. Tamping Rod: 10 mm in diameter and 230 mm long8. Balance of capacity not less than 500g and readable to a accuracy of 0.1g.9. A well ventilated thermostatically controlled oven.

Fig.1 Aggregate Impact Testing Machine

RELEVANT CODES: IS: 2386 (Part IV)-1963: (Reaffirmed 2007) Methods of Aggregate for concrete; Determination of Aggregate Impact value; Bureau of Indian Standards

PROCEDURE:1. The test sample should be passed through a 12.5-mm IS Sieve and retained on a 10-mm IS Sieve. 2. The aggregate comprising the test sample should then be dried in an oven for a period of four hours at a temperature of 100 to 110C and cooled. 3. The measure should be filled in three layers by tamping each layer with 25 strokes of the tamping rod till it overflows and the surplus aggregate should be struck off using the tamping rod as a straight edge. 4. The net weight of aggregate in the measure shall be determined to the nearest gram and this weight of aggregate shall be used for the duplicate test on the same material.5. The cup is to be fixed firmly in position on the base of the machine and with the hole of the test sample placed in it; it is to be compacted by a single tamping of 25 strokes of the tamping rod.6. The hammer should be raised up to a height of 380 mm above the surface of the aggregate in the cup and allowed to fall freely on the sample for 15 times.7. The crushed aggregate should be now sieved through a 2.36 mm sieve until there is no significant passes in one minute.8. The fraction passing the sieve shall be weighed to an accuracy of 0.1 g. The fraction retained on the sieve shall also be weighed and, if the total weight is less than the initial weight by more than one gram, the result shall be discarded and a fresh test made. Two tests shall be made.

PRECAUTIONS: Use hand gloves while removing containers from oven after switching off the oven. To wear safety shoes & goggles at the time of testing. Before testing, machine should be properly checked. Special care should be taken that no outer air enters when using the balance. After test clean the sieve by a smooth brush. Keep the guide rods firmly fixed to the base & top plate.

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