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 formed in terms of the total weight of the sample is expressed as the aggregate impact value.
General Description & Specification :
Consists of base weighing between 20-30 kg with a lower surface of not less than 30cm and support columns to form a rigid framework around the quick-release trigger mechanism to ensure an effective free fall of the hammer during test. The free fall can be adjusted through 380 + 5.0mm. The hammer is provided with a locking arrangement. A metal tup (hammer) weighing 13.5 to 14.0 kg, the lower end of in cylindrical shape, 100mm in diameter and 5cm long with a 2mm chamfer at the lower edge and case hardened. Complete with a cylindrical cup, 102mm Dia x 50mm depth, one measure 75mm Dia x 50mm deep and a tamping rod of circular cross section 10mm in diameter and 230mm long, rounded at one end.
The following accessories are not part of the standard supply and are supplied at an extra cost.
- Test Sieve 10mm, 12.5mm and 2.36mm opening.
- Laboratory Oven.
- Automatic Blow Counter.
- Electronic Balance 500gm x 100 mg / Two Pan Balance.
Procedure to determine Aggregate Impact Value
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.
Aggregate impact value = (B/A) x 100%
iii) Two such tests should be carried out and the mean of the results should be reported.