Crushing value test (IS 2386 part 4).
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. 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:
Aggregates crushing value =(B/A)*100
Where A=weight of fraction passing the appropriate sieves.
B=weight of surface dry sample.
Ten percent fineness test (IS 2386 Part 4)
The ten per cent fines value gives a measure of the resistance of an aggregate to crushing, that is, applicable to all aggregates.
The material for the test consists of surface-dry aggregate passing a 12.5 mm sieve and retained on a 10 mm sieve. The weight of material comprising the test sample is determined (weight A).
The cylinder of the test apparatus is put in position 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 inserted so that it rests horizontally on this surface, care being taken to ensure that the plunger does not jam in the cylinder.
The apparatus with the test sample and plunger in position is then placed in the compression testing machine. The load is applied at a uniform rate so as to cause a total penetration of the plunger in 10 minutes of about: 15.0 mm for rounded or partially rounded aggregate (for example, uncrushed gravels), 20.0 mm for normal crushed aggregate, and 24.0 mm for honeycombed aggregate (for example, expanded shales and slags).
These figures may be varied according to the extent of the rounding or honeycombing. After reaching the required maximum penetration, the load is released and the whole of the material removed from the cylinder is sieved on a 2.36 mm sieve. The fines passing the sieve are weighed, and expressed as a percentage of the weight of the test sample.
Normally, this percentage will fall within the range 7.5 to 12.5, but if it does not, a further test is made at a load adjusted as seems appropriate to bring the percentage fines within the range of 7.5 to 12.5.
The mean percentage fines from the two tests at this load are used in the following formula to calculate the load required to give 10 per cent fines:
Load required for 10 per cent fines = 14x/y+4
Where x = loads in tonnes
y= mean percentages fines from two test at x tonnes.
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