Aggregate impact value

AIM
To determine the aggregate impact value of coarse aggregates as per
IS: 2386 (Part IV) - 1963.

APPARATUS
AGGREGATE IMPACT TEST MACHINE
  1. Impact testing machine conforming to IS: 2386 (Part IV) - 1963
  2. IS Sieves of sizes - 12.5mm, 10mm and 2.36mm
  3. A cylindrical metal measure of 75mm dia. and 50mm depth
  4. A tamping rod of 10mm circular cross section and 230mm length, rounded at one end
  5. Oven 
PREPARATION OF SAMPLE 
  1. The test sample should conform to the following grading: - Passing through 12.5mm IS Sieve 100% - Retention on 10mm IS Sieve 100%
  2. The sample should be oven-dried for 4hrs. at a temperature  of 100 to 110oC and cooled.
  3. The measure should be about one-third full with the prepared  aggregates and tamped with 25 strokes of the tamping rod.  A further similar quantity of aggregates should be added and  a further tamping of 25 strokes given. The measure should  finally be filled to overflow, tamped 25 times and the surplus aggregates struck off, using a tamping rod as a straight edge. The net weight of the aggregates in the measure should be determined to the nearest gram (Weight 'A'). 
PROCEDURE
  1. The cup of the impact testing machine should be fixed firmly in position on the base of the machine and the whole of the test sample placed in it and compacted by 25 strokes of the tamping rod.
  2. The hammer should be raised to 380mm above the upper surface of the aggregates in the cup and allowed to fall freely onto the aggregates. The test sample should be subjected to a total of 15 such blows, each being delivered at an interval of not less than one second. 
REPORTING OF RESULTS 
  1. The sample should be removed and sieved through a 2.36mm IS Sieve. The fraction passing through should be weighed (Weight 'B'). The fraction 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 should be discarded and a fresh test done.
  2. The ratio of the weight of the fines formed to the total sample weight should be expressed as a percentage.
                                           B
Aggregate impact value = ——– x 100%
                                           A


   3. Two such tests should be carried out and the mean of the results should be reported.

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