Impact value of aggregate is an important test in your engineering lab.When you design pavements, the impact load is one of the challenging factors that you need to face.To determine the aggregate impact value the required apparatus are given below.
Apparatus required for aggregate impact value test
i) Impact testing machine conforming to IS: 2386 (Part IV) – 1963
ii) IS Sieves of sizes – 12.5mm, 10mm, and 2.36mm
iii) A cylindrical metal measure of 75mm dia. and 50mm depth
iv) A tamping rod of 10mm circular cross-section and 230mm length, rounded at one end
How can sample for aggregate impact value test be prepared?
1.The test sample is consist of the following grading: – Passing through 12.5mm IS Sieve 100% – Retention on 10mm IS Sieve 100%
2.The sample is oven-dried for 4hrs. at a temperature of 100 to 110oC and cooled.
3.The measure is about one-third full with the prepared aggregates and tamped with 25 strokes of the tamping rod.
4.A further similar quantity of aggregates is added and a further tamping of 25 strokes given. The measure is finally to be filled to overflow, tamped 25 times and the surplus aggregates struck off, using a tamping rod as a straight edge.
5.The net weight of the aggregates in the measure is determined to the nearest gram (Weight ‘A’).
Procedure for aggregate impact value test
i) The cup of the impact testing machine is fixed firmly in position on the base of the machine and the whole of the test sample is placed in it and compacted by 25 strokes of the tamping rod.
ii) The hammer is raised to 380mm above the upper surface of the aggregates in the cup and allowed to fall freely onto the aggregates.
iii) The test sample is subjected to a total of 15 such blows, each being delivered at an interval of not less than one second.
iv) The sample is removed and sieved through a 2.36mm IS Sieve. The fraction passing through is weighed (Weight ‘B’).
v) The fraction is retained on the sieve should also be weighed (Weight ‘C’) and if the total weight (B+C) is less than the initial weight (A) by more than one gram, the result is discarded and a fresh test is done.
vi) The ratio of the weight of the fines formed to the total sample weight is expressed as a percentage.
vii) Aggregate impact value is obtained by the relation (B/A) x 100%
viii) Two such tests are carried out and the mean of the results is reported.
Observation in this experiment
The Aggregate Impact Value can be found by referring to below table.