How impact value of coarse aggregate is determined

Impact value of coarse aggregate plays an important role to find out the moisture content of coarse aggregate.

For this purpose, the following equipments are required :-

1) Impact testing machine (metal base)

2) A cylindrical steel cup of internal dimension: 102mm & depth 50mm.

3) IS sieves of sizes 12.5, 10 & 2.36mm.

4) A straight metal tamping rod having circular cross section 16mm in dia. And 600mm long rounded at one end.

5) Weight balance of 01 gm.

6) A relevant oven thermostatically controlled to retain a temperature of 100°C to 110°C Samples:

1. i) Coarse Aggregate

The following methods should be applied :-

1. The impact machine stands devoid of wedging or packing upon the level plate.
2. The cup should be attached rigidly in exact location on the base of the machine and entire test sample should arranged in it depending on fifteen blows of the metal hammer of weight 14 kg downfallen from a height of 38 cm.
3. The quantity of fine material that goes through 2.36mm resultantly from pounding will point out the strength of the sample of aggregate. The proportion of the weight of the fines (finer than 2.36mm size) developed to be taken as weight of the total sample selected is stated as a percentage. It is called as aggregate impact value as per IS 283-1970


Aggregate impact value does not surpass 45 percent by weight for aggregate utilized for concrete apart from wearing surface and 30 percent by weight for concrete for wearing surface like run way, roads and pavements.

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How impact value of coarse aggregate is determined