Ten Percent Fines Value

The ten percent fines value is a measure of an aggregate’s resistance to crushing, and it is applicable to all aggregates. This test is quite similar to the aggregate crushing test, which measures the amount of fines material crushed as a percentage of the initial mass.

When aggregate is subjected to mechanical degradation, its characteristics can be disclosed using a 10% fines value.

Apparatus

1. A 15.2 cm diameter steel cylinder with a plunger and a base plate.
2. A straight metal tamping rod with a circular cross-section of 16 mm in diameter and a height of 45 to 60 cm, rounded at one end.
3. IS sieves with diameters of 12.5, 10, and 2.36 mm.
4. A 3 kilogram capacity balance that is readable and accurate to one gram.
5. A compression testing machine capable of applying a load of 50 tonnes and operating at a consistent rate of loading to achieve the maximum load in 10 minutes. This load may vary from 0.5 to 50 tonnes.
6. Cylindrical metal measure with enough strength to withstand hard use, 11.5 cm diameter, and 18 cm height.
7. Dial Gauge

Preparation of Sample

1. The material for the standard test must be aggregate that passes a 12.5 mm IS Sieve and is retained on a 10 mm IS Sieve, and
2. It must be properly separated on these sieves before testing.
3. The aggregate shall be tested in a surface-dry condition. If necessary, the aggregates can be dried by heating at 100°C – 110°C for not more than 4 hours and cooled to room temperature before testing.
4. 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 with the tamping rod as a straight-edge, gives the necessary quantity.
5. The weight of the material that comprises up the test sample (Weight A) must be calculated, and
6. The same weight of sample must be used for the repeat test.

Procedure

1. Place the cylinder on the base plate and weigh it (Initial Weight W).
2. Arrange the sample in three layers, with each layer undergoing 25 strokes with the tamping rod. In the case of weak materials, care must be taken not to shatter the particles and weigh them (Weight W1).
3. Carefully level the aggregate surface and insert the plunger so that it lies horizontally on the surface. The plunger is being carefully monitored to ensure that it does not become stuck in the cylinder.
4. Place the cylinder with plunger on the compression testing machine’s loading platform.
5. Apply an uniform rate of load such that a total load of 50 Tonnes is applied in 10 minutes is approximately:
   • 15.0 mm for rounded or partially rounded aggregates
   • 20.0 mm for normal crushed aggregates, and
   • 24.0 mm for honeycombed aggregates
6. Release the load
7. Remove the material from the cylinder.
8. Using a 2.36 mm IS sieve, sieve the material. Weigh this fraction going through it to 0.1 gram precision. This fraction represents the quantity of material lost due to crushing. Determine the proportion that passes through the IS sieve as (Weight W2).

Note: About 6.5 kg of natural aggregate is required to provide the two test samples. It takes less light-weight aggregate.

In each test, the weight of fines generated to total sample weight must be represented as a percentage of the weight of the test sample.

using, Aggregate Crushing Value = 100(W2/W1) percent

where,

W2 = Weight of fraction passing the appropriate 2.36 mm IS sieve, and

W1 = Weight of surface-dry sample.

Normally, this percentage will fall between 7.5 and 12.5, but if it does not, a new test at a load adjusted as required to bring the percentage fines within the range of 7.5 to 12.5.

Observations

The mean percentage fines from the two tests at this load must be used in the following calculation to determine the load required to produce 10% fines:

Load required for 10 percent fines = (14xA)/(B+4)

where,

A = Load in tonnes, and

B = Mean percentage fines from two tests at A tonnes load.

Final Verdict

The load required to produce 10% fines must be recorded to the closest whole number for loads of 10 tonnes or more, and to the nearest 0.5 tonne for weights less than 10 tonnes.

Reference

1. IS : 2386 (Part IV) – 1963 – Methods of Test for aggregates for Concrete – Part IV : Mechanical Properties

If you like this article, please do share this with your friends

And, tell us your queries in the below comment box.

Also Read: Aggregate Crushing Value Test