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

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

v) Oven

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').

PROCEDURE

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.

REPORTING OF RESULTS

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.

B

Aggregate impact value = ——– x 100%

A

iii) Two such tests should be carried out and the mean of the

results should be reported.