The aggregate crushing value gives a relative measure of the resistance of an aggregate to crushing apply a gradually increasing compressive load. The strength of aggregate is calculated by the crushing value test. The aggregates used should be strong enough to with stand the stresses which comes on to it.
Aggregate are the important part of concrete. Aggregates contribute to a majority of proportion (70- 80 %) in concrete and thus responsible for the increase in weight of concrete. They give body of the concrete, reduce shrinkage and effect economy. Earlier researchers consider aggregate as an inert material but now its not the case. Aggregates can also have chemically active materials in it.
Test for determination of aggregate crushing value
Apparatus for aggregate crushing value:
- Steel cylinder with open ends
- cylindrical measure having internal diameter 115 mm and height 180 mm
- Steel tamping rod
- Balance
- Compression testing machine
Procedure :
- Collect aggregate passing from 12.5 mm and retained in 10 mm I.S. sieve.
- Weigh about 6.5 kg of aggregate obtain from the step 1.
- The aggregate in surface dry condition is filled in standard cylinder in three layers.
- After each layer , tamp 25 times for good compaction.
- Then take the weight of the cylinder with aggregate.
- Place the apparatus, with the test sample and plunger in position on the compression testing machine.
- Apply the compressive load of 40 tons in 10 mins.
- Then remove the specimen from machine and sieve the aggregates through 2.36 mm.
- Then weigh the aggregates passing through the sieve and express it as a percentage of total aggregates taken.
$$ The \,aggregate \,crushing \,value =\frac{ weight\, of \,aggregate\, passing \,through \,2.36 mm \,sieve}{weight \,of \,total \,surface\, dry\, aggregate\, taken\, in\, mould} $$
The aggregate crushing value should not be more than 45 % for concrete
Check this post for different tests available for aggregate.
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