IS: 2386 - Part 4 

1. Introduction

The aggregate impact value (AIV) indicates a relative measure of the resistance of the aggregate to sudden impact or shock, which differs from its resistance to slow compressive load. This method covers the procedure for determining the aggregate impact value of coarse aggregate.

2. Apparatus

(i) Aggregate Impact Testing machine which consists of a heavy metal base, detachable cylindrical steel cup 10. 2 cm dia and 5.0 cm height which can be secured to the base, a metal hammer of weight 13.5 kg to 14.0 kg, moving between vertical guides with lower end cylindrical in shape which can fall freely into the cup. There is arrangement to raise the hammer and drop from a height of 38±0.5 cm. A key is provided to lock the hammer while fastening or removing the cup.

(ii) A cylindrical metal measure having internal dia 7.5 cm and depth 5.0 cm for measuring the required quantity of test sample.

(iii) A straight metal tamping rod of circular cross section, 1.0 cm in dia and 23.0 cm long, rounded at one end.

(iv) IS sieves of sizes 12.5 mm, 10.0 mm and 2.36 mm for sieving aggregates.

(v) A balance of capacity not less than 500 gm with sensitivity of 0.1 gm.

(vi) Drying oven, thermostatically controlled, capable of maintaining temperatures of 100°C to 110°C

3. Procedure

a) Test samples of aggregate passing 12.5 mm and retaining on 10.0 mm sieve is dried in the oven for four hours at 105±5°C and cooled to room temperature.

b) The measuring cup is filled with the sample aggregates to one-third full and given 25 tamping with the tamping rod.

c) Another layer to reach up to two-third of the cup is filled and given 25 tamping.

d) The measure is then filled to over flow and tamped 25 times. Struck off the excess aggregates using the tamping rod as straight edge.

e) The net weight of the aggregate is determined and the same weight of aggregate is used for the duplicate test.

f) The steel cup is now clamped to the base and the whole sample in the measure is transferred to the steel cup.

g) 25 tamping are given to the sample in the steel cup.

h) The hammer is raised, until its lower face is 380 mm above the above the upper surface of the aggregate sample in the cup, and allowed to fall freely on the aggregates.

i) The test sample is subjected to a total number of 15 such blows and each delivered at an interval of not less than one second. 

j) The crushed aggregate is removed from the steel cup and sieved through 2.36 mm sieve till no significant amount of material pass.

k) The fraction passing the sieve is weighed accurately to the nearest 0.1 gm. The weight retained is also determined and the total should agree with the weight of sample taken for test.  If the difference is more than 1.0 gm, the sample is discarded and test shall be repeated.

l) Another sample of similar weight is taken and the test is carried on this second sample also.

4. Calculations

The aggregate impact value is expressed as a percentage of the fines formed against the weight of sample tested.

Let the weight of sample taken = W1 gm.

Weight of material passing 2.36 mm sieve = W2 gm.

Aggregate impact value = (W2/W1) x 100 percent.

The mean of the 2 results rounded to the nearest whole number is reported as the aggregate impact value (AIV) of the tested material.