Determination of Aggregate Abrasion Value

Objective : This method of test methods of determining the abrasion value of coarse aggregate, by the use of Los Angeles machine.

Reference : IS : 2386 ( Part IV) – 1963, IS: 383-1970

Theory : Abrasive Charge-The abrasive charge shall consist of cast iron spheres or steel spheres approximately 48 mm in. diameter and each weight between 390 and 445 g.

The test sample consist of clean aggregate which has been dried in an oven at 105°C to 110°C and it should conform to one of the gradings shown in Table 3.22.

Apparatus :
Los Angeles machine - The Los Angeles abrasion testing machine shall consist of a hollow steel cylinder, closed at both ends, having an inside diameter of 700 mm and an inside length of 500 mm. The cylinder shall be mounted on stub shafts attached to the ends of the cylinders but not entering it, and shall be mounted in such, a manner that it may be rotated about its axis in a horizontal position. An opening in the cylinder shall be provided for the introduction of the test sample. A removable steel shelf, projecting radially 88 mm into the cylinder and extending its full length, shall be mounted along one element of the interior surface of the cylinder. The shelf shall be of such thickness and so mounted, by bolts or other approved means, as to be firm and rigid. The 1.70 mm IS Sieve.

Figure :

Procedure :
1. The test sample shall consist of clean aggregate which has been dried in an oven at 105 to 110°C to substantially constant weight and shall conform to one of the gradings shown in Table 3.22. The grading or gradings used shall be those most nearly representing the aggregate furnished for the work.

2. The test sample and the abrasive charge shall be placed in the Los Angeles abrasion testing machine and the machine rotated at a speed of 20 to 33 rev/min. For gradings A, B, C and D, the machine shall be rotated for 500 revolutions; for gradings E, F and G, it shall be rotated for 1 000 revolutions.

3. The machine shall be so driven and so counter-balanced as to maintain a substantially uniform peripheral speed. If an angle is used as the shelf, the machine shall be rotated in such a direction that the charge is caught on the outside surface of the angle.

4. At the completion of the test, the material shall be discharged from the machine and a preliminary separation of the sample made on a sieve coarser than the l.70 mm IS Sieve.

5. The material coarser than the 1.70 mm IS Sieve shall be washed dried in an oven at 105 to 110°C to a substantially constant weight, and accurately weighed to the nearest gram.

Calculation :
The difference between the original weight and the final weight of the test sample is expressed as a percentage of the original weight of the test sample. This value is reported as the percentage of wear.

Aggregate Abrassion Value=B/A*100

B weight in g of fraction passing through 1.70 mm IS Sievs
A weight in g of saturated surface - dry sample,

Conclusion / Result :
The aggregate Abrasion Value of given sample of coarse aggregate is ……….. %
The percentage of wear should not be more than 16 per cent for concrete aggregates.

Determination of Aggregate Impact Value

Objective : This method of test covers the procedure for determining the aggregate impact
value of coarse aggregate.

Reference : IS : 2386 ( Part IV) – 1963, IS: 383-1970

Theory : The aggregate impact value‘ gives a relative measure of the resistance of an aggregate to sudden shock or impact, which in some aggregates differs from its resistance to a slow compressive load.

Apparatus : An impact testing machine of the general form shown in Fig. 2 and complying with the following:

1. A cylindrical steel cup of internal dimensions: Diameter 102 mm, Depth 50 mm and not less than 6.3 mm thick

2. A metal hammer weighing 13.5 to 14.0 kg, the lower end of which shall be cylindrical in shape, 100.0 mm in diameter and 5 cm long, with a 2 mm chamber at the lower edge, and case-hardened. The hammer shall slide freely between vertical guides so arranged that the lower (cylindrical) part of the hammer is above and concentric with the cup.

3. Means for raising the hammer and allowing it to fall freely between the vertical guides from a height of 380.0 mm on to the test sample in the cup, and means for adjusting the height of fall within 5 mm. Sieves-The IS Sieves of sizes 12.5, 10 and 2.36 mm, Tamping Rod, balance of capacity not less than 500 g, Oven etc.

Procedure : 
1. The test sample shall consist of aggregate the whole of which passes a 12.5 mm IS Sieve and is retained on a 10 mm IS Sieve. The aggregate comprising the test sample shall be dried in an oven for a period of four hours at a temperature of 100 to 110°C and cooled.

2. The measure shall be filled about one-third full with the aggregate and tamped with 25 strokes of the rounded end of the tamping rod. The net weight of aggregate in the measure shall be determined to the nearest gram (Weight A)

3. The impact machine shall rest without wedging or packing upon the level plate, block or floor, so
that it is rigid and the hammer guide columns are vertical.

4. The cup shall be fixed firmly in position on the base of the machine and the whole of the test sample placed in it and compacted by a single tamping of 25 strokes of the tamping rod.

5. The hammer shall be raised until its lower face is 380 mm above the upper surface of the aggregate
in the cup, and allowed to fall freely on to the aggregate. The test sample shall be subjected to a total
of 15 such blows each being delivered at an interval of not less than one second.

6. The crushed‘ aggregate shall then be removed from the cup and the whole of it sieved on the 2.36
mm IS Sieve until no further significant amount passes in one minute. The fraction passing the sieve
shall be weighed to an accuracy of 0.1 g (Weight. B).

7. The fraction retained on the sieve shall also be weighed (Weight C) and, if the total weight (C+B) is less than the initial weight (Weight A) by more than one gram, the result shall be discarded and a
fresh test made. Two tests shall be made.

Calculation :
The ratio of the weight of fines formed to the total sample weight in each test shall he expressed as a
percentage, the result being recorded to the first decimal place:

Aggregate Impact Value=B/A*100

B weight in g of fraction passing through 2.36 mm IS Sievs
A weight in g of saturated surface - dry sample,

Conclusion / Result :
The aggregate Impact value of given sample of coarse aggregate is ……….. %
The aggregate impact 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.

Determination of Aggregate Crushing value

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.