The crushing value of aggregate is very important to know the strength of the aggregate. For finding the resistance of aggregate under gradually applied compressive load, the crushing value test of aggregate is done. For the crushing value test, the following procedure is followed.
Procedure for finding the crushing value of aggregate.
- Aggregate passing through a12.5mm I.S. sieve and retained on 10mm I.S. sieve is taken.
- About 6.5
kgmaterial is taken.
- The aggregate in a surface dry condition is filled into the standard cylindrical measure in three layers approximately of equal depth.
- Each layer is tamped 25 times with the tamping rod as a straight edge.
- The weight of the sample contained in the cylinder measure is taken (A).
- The cylinder of the test apparatus with aggregate filled in a standard manner is put in position on the base-plate and the aggregate is carefully leveled and the plunger inserted horizontally on this surface. The plunger should not jam in the cylinder.
- The apparatus, with the test sample and plunger in position, is placed on the compressive testing machine and is loaded uniformly up to a total load of 40 tons for 10 minutes time.
- The load is then released and the whole of the material is removed from the cylinder and sieved on 2.36mm I.S. sieve. The fraction passing the sieve is weighed (B).
The aggregate crushing value= B/A*100
Where,B is weightof fraction passing 2.36mm sieve
- A is
weightof surface dry sample taken in . mould
- The aggregate crushing value should not be more than 45% for aggregate used for concrete other than the wearing surfaces.
- 30% for concrete used
the surfacessuch as runway, roads and air fieldpavements.