Objective:
This method of test covers the procedure for determining the aggregate crushing value of coarse aggregate.
Reference :
IS : 2386 ( Part IV) – 1963, IS: 383-1970
Theory :
The aggregate crushing value‘ gives a relative measure of the resistance of an aggregate to crushing under a gradually applied compressive load. With aggregate of aggregate crushing value‘ 30 or higher, the result may be anomalous, and in such cases the ten percent fines value‘ should be determined instead.
Apparatus:
A 15-cm diameter open-ended steel cylinder, with plunger and base-plate, of the general form and dimensions shown in Fig. ,A straight metal tamping rod, A balance of capacity 3 kg, readable and accurate to one gram, IS Sieves of sizes 12.5, 10 and 2.36 mm, For measuring the sample, cylindrical metal measure of sufficient rigidity to retain its form under rough usage and of the following internal dimensions: Diameter 11.5 cm and Height 18.0 cm.
Procedure :
1. The material for the standard test shall consist of aggregate passing a 12.5 mm IS Sieve and retained on a 10 mm IS Sieve, and shall be thoroughly separated on these sieves before testing.
2. The aggregate shall be tested in a surface-dry condition. If dried by heating, the period of drying shall not exceed four hours, the temperature shall be 100 to 110°C and the aggregate shall be cooled to room temperature before testing.
3. The appropriate quantity may be found conveniently by filling the cylindrical measure in three layers of approximately equal depth, each layer being tamped 25 times with the rounded end of the tamping rod and finally leveled off, using the tamping rod as a straight-edge.
4. The weight of material comprising the test sample shall be determined (Weight A) and the same
weight of sample shall be taken for the repeat test.
5. The apparatus, with the test sample and plunger in position, shall then be placed between the platens of the testing machine and loaded at as uniform a rate as possible so that the total load is reached in 10 minutes. The total load shall be 400 kN.
6. The load shall be released and the whole of the material removed from the cylinder and sieved on a
2.36 mm IS Sieve for the standard test. The fraction passing the sieve shall be weighed (Weight B).
Calculation :
The ratio of the weight of fines formed to the total sample weight in each test shall be expressed as a
percentage, the result being recorded to the first decimal place:
Aggregate Crushing Value =B/A*100
B=weight in g of fraction passing through appropriate sieves
A=weight in g of saturated surface - dry sample,
Conclusion / Result :
The aggregate crushing value of given sample of coarse aggregate is ……….. %
The aggregate crushing value should not be more than 45 percent for aggregate used for concrete other
than for wearing surfaces, and 30 percent for concrete used for wearing surfaces such a runways, roads and air field pavements.
This method of test covers the procedure for determining the aggregate crushing value of coarse aggregate.
Reference :
IS : 2386 ( Part IV) – 1963, IS: 383-1970
Theory :
The aggregate crushing value‘ gives a relative measure of the resistance of an aggregate to crushing under a gradually applied compressive load. With aggregate of aggregate crushing value‘ 30 or higher, the result may be anomalous, and in such cases the ten percent fines value‘ should be determined instead.
Apparatus:
A 15-cm diameter open-ended steel cylinder, with plunger and base-plate, of the general form and dimensions shown in Fig. ,A straight metal tamping rod, A balance of capacity 3 kg, readable and accurate to one gram, IS Sieves of sizes 12.5, 10 and 2.36 mm, For measuring the sample, cylindrical metal measure of sufficient rigidity to retain its form under rough usage and of the following internal dimensions: Diameter 11.5 cm and Height 18.0 cm.
Procedure :
1. The material for the standard test shall consist of aggregate passing a 12.5 mm IS Sieve and retained on a 10 mm IS Sieve, and shall be thoroughly separated on these sieves before testing.
2. The aggregate shall be tested in a surface-dry condition. If dried by heating, the period of drying shall not exceed four hours, the temperature shall be 100 to 110°C and the aggregate shall be cooled to room temperature before testing.
3. The appropriate quantity may be found conveniently by filling the cylindrical measure in three layers of approximately equal depth, each layer being tamped 25 times with the rounded end of the tamping rod and finally leveled off, using the tamping rod as a straight-edge.
4. The weight of material comprising the test sample shall be determined (Weight A) and the same
weight of sample shall be taken for the repeat test.
5. The apparatus, with the test sample and plunger in position, shall then be placed between the platens of the testing machine and loaded at as uniform a rate as possible so that the total load is reached in 10 minutes. The total load shall be 400 kN.
6. The load shall be released and the whole of the material removed from the cylinder and sieved on a
2.36 mm IS Sieve for the standard test. The fraction passing the sieve shall be weighed (Weight B).
Calculation :
The ratio of the weight of fines formed to the total sample weight in each test shall be expressed as a
percentage, the result being recorded to the first decimal place:
Aggregate Crushing Value =B/A*100
B=weight in g of fraction passing through appropriate sieves
A=weight in g of saturated surface - dry sample,
Conclusion / Result :
The aggregate crushing value of given sample of coarse aggregate is ……….. %
The aggregate crushing value should not be more than 45 percent for aggregate used for concrete other
than for wearing surfaces, and 30 percent for concrete used for wearing surfaces such a runways, roads and air field pavements.
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