Aggregate Crushing Value

Dnyan Deshmukh

Staff member
Aggregate-Crushing-Value-75mm.jpg

Ref : IS : 2386 (Part IV)

Purpose : To determine the crushing value of aggregates.

Significance : The aggregate crushing value gives relative measure of the resistance to

crush under a gradually applied compressive load.

Definition : It is defined as the ratio of the weight of fines to the total sample weight

expressed as a percent when tested as per the IS procedure.

Apparatus : Steel cylinder with open ends, Cylindrical measure, Steel tamping rod,

Balance, Compression testing machine.


Preparation of sample:


a) Take a sample of about 6.5 Kg aggregate for 150mm diameter cylinder and 1 Kg for 75mm diameter cylinder, passing through 12.5mm and retained on 10mm sieves for 20mm down aggregate and passing through 6.3mm sieve and retained on 4.75mm sieve for 10mm down aggregate, to provide two test samples.

b) Dry the aggregate at the temperature of 100 0C to 110 0C and then cool at room temperature.

c) Fill up the cylindrical measure in three equal depth layers by tamping each layer 25 times by tamping rod.

d) Take weight (A) of aggregate sample.


Procedure:


a) Add the test sample in three layers. Compact each layer by 25 strokes of tamping rod.

b) Level the surface of the aggregate and insert the plunger.

c) Place the apparatus with the test sample and plunger in position between the platens of the testing machine.

d) Apply uniform load, so that load is reached in 10 minutes. The total load shall be 40 tonnes for 20mm down aggregate and 10 tonnes for 10mm down aggregate.

e) Release the load and remove the whole material from the cylinder.

f) Sieve the material on 2.36mm sieve for 20mm down aggregate and on 1.18mm sieve for 10mm down aggregate.

g) Take weight (B) of material passing through is 2.36mm sieve for 20mm down aggregate and 1.18mm sieve for 10mm down aggregate.


Calculation:


Aggregate Crushing Value (%) = (B) x 100

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(A)
 

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