Crushing Value Test (IS: 2386 (Part IV))
The material for the test should consist of aggregate passing 12.5 mm sieve and retained on 10 mm sieve. For other sizes, the materials are separated on the appropriate sieves given in Table .
Table 10 Details of Aggregate Crushing Test for Non-standard Sizes of Aggregate
Note: About 6500 g of natural aggregate is required to provide samples for the 150 mm cylinder, or about 1000 g for the 75 mm cylinder.
The aggregate is tested in a surface-dry condition. The weight of material comprising the test sample is determined (weight A).
The cylinder of the test apparatus is positioned on the base-plate and the test sample is added in thirds, each being subjected to 25 strokes from the tamping rod. The surface of the aggregate is carefully levelled and the plunger is inserted so that it rests horizontally on this surface.
The apparatus, with the test sample and plunger in position is then placed between the platens of the testing machine and loaded at an uniform rate as possible, so that the total load is reached in 10 minutes. The total load should be 400 kN.
The load is released and the whole of the material is removed from the cylinder and sieved on a 2.36 mm sieve for the standard test, or on the appropriate sieve given in Table 6.5. The fraction passing the sieve is weighed.
The ratio of the weight of fines formed to the total sample weight in each test is expressed as a percentage, recorded to the first decimal place:
Aggregate crushing value = B/A ¥ 100
B = weight of fraction passing the appropriate sieve
A = weight of surface-dry sample