To determine the aggregate impact value of coarse aggregates as per IS: 2386 (Part IV) – 1963.
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
PREPARATION OF SAMPLE:
i) The test sample should conform to the following grading:
– Passing through 12.5mm IS Sieve 100%
– Retention on 10mm IS Sieve 100%
ii) The sample should be oven-dried for 4hrs. at a temperature of 100 to 110oC and cooled.
iii) 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’).
i) 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.
ii) 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.
i) 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.
ii) The ratio of the weight of the fines formed to the total
sample weight should be expressed as a percentage.
Aggregate impact value = B/A x 100%
iii) Two such tests should be carried out and the mean of the results should be reported.
A sample proforma for the record of the test results is given in the below table.
APPLICATION S OF AGGREGATE IMPACT VALUE
- Aggregate having AIV % less 50% is better to use in construction where as those having value more than 50% are bad for construction.
- It is reliable to calculate the AIV % of the aggregate use as road construction as it will give us the capacity of road to bear the load on it. Aggregate having AIV % equal or greater than 35 % is considered bad to use in road construction.
PURPOSE OF TEST:
Aggregate Impact Value test determines the Aggregate Impact Value (AIV) of aggregates which provides a relative measure of the resistance of an aggregate to sudden shock or impact.
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.
Lower the aggregate crushing value greater will be the “resistance to to sudden shock or impact (toughness)”.
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