How to determine the soft particles in coarse aggregates?

There is a method of aggregate-test which deals with the procedure of determining the quantity of soft particles in coarse aggregates on the basis of scratch-hardness. This method is intended to be used to identify material that are soft, including those which are so poorly bonded that the separate particles in the piece are easily detached from the mass.

The test is not intended to identify other types or deleterious materials in aggregates.


Soft Particles in Coarse Aggregates as per IS: 2386 Part-2
Soft Particles in Coarse Aggregates

Determination of Soft Particles in Coarse Aggregates as per IS: 2386 Part-2


Hi friends, you are welcomed in the world of Civil Allied Gyan. Here I have explained about determination of lightweight pieces (coal and lignite) in aggregate. Read definition, apparatus list, IS code, test procedure, formula, result, lab report about determination of soft particles in coarse aggregates.


IS Code for Determination of Soft Particles in Coarse Aggregates:-

  • IS: 2386 (Part-2) 1963, Method of estimation of deleterious materials and organic impurities.


Apparatus Required for Determination of Soft Particles in Coarse Aggregates:-

  • A brass rod of 1·6 mm diameter with Rockwell hardness of 65 RHB to 75 RHB inserted into the wood shaft of an ordinary lead pencil.
  • IS Sieves of size 50 mm, 40 mm, 25 mm, 20 mm, 12.5 mm and 10 mm.


Sampling of the Test Specimen:-

The test sample of aggregates shall consist of all material from which the sizes finer than the 10-mm IS Sieve have been removed. The test sample shall be of such size that it will yield not less than the following amounts of the different sizes.

Sample should be available in amounts of 10 % or more:

Sieve Size in mm (Square Opening Sieves)

Sample Weight in gram

Over 10 to 12·5

200

Over 12·5 to 20

600

Over 20 to 25

1500

Over  25 to 40

4500

Over 40 to 50

12000


If the test sample of aggregate contains less than 10 % of any of the sizes specified under the above table, the size shall not be tested but, for the purpose of calculating the test results, it shall be considered to contain the same percentage of the soft particles as the average of the next smaller and the next larger size. If one of these sizes is absent, it shall be considered to have the same percentage of soft particles as the next larger or next smaller size, whichever is present.



Procedure for Determination of Soft Particles in Aggregates:-

  1. Each particle of aggregates shall be scratched with the brass rod using about 1 kg of pressure.
  2. Particles are considered as soft particles if a groove is made in them without deposition of metal from the brass rod or if the separate particles are detached from the rock mass, during the scratching process.

  3. Weight and number of particles of each size of each sample classified as soft in the test (let m₁, m₂, m₃, m₄, m are their weight and n, n, n, n, nare numbers).
  4. Weight and number of particles of each size of each sample tested with the brass rod (let M₁, M₂, M₃, M₄, M are their weight and N, N, N, N, Nare numbers).

Note:- In the case of some sandstones, brass fragments may be deposited on hard individual grains while at the same time separate particles are detached from the mess due to a weak binding medium. Such particles are to be considered as soft particles.



Calculation for Soft Particles in Aggregates:-

Percentage of soft particles classified as by weight and by number of particles using given formula.

Formula for soft particles in coarse aggregates:-


Soft Particles in Coarse Aggregates as per IS: 2386 Part-2


Report for Soft Particles in Aggregates:-

Weighted average percentage of soft particles calculated from the calculated percentage and based on the grading of sample of aggregate received for examination or, preferably, on the average grading of the material from that portion of the supply of which the sample is representative. In these calculations, sizes finer than the 10-mm IS Sieve shall not be included.


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