Methodology for Aggregate Gradation Test

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The aggregate gradation test is conducted to determine the distribution of particle sizes in a given aggregate sample. The procedure for conducting this test in India is outlined by the Bureau of Indian Standards (BIS). As of my last knowledge update in January 2022, the relevant standard is IS 2386 (Part 1): 2016, “Methods of Test for Aggregates for Concrete – Part 1: Particle Size and Shape.”

Please note that standards may be revised, and new versions may be released, so it’s crucial to check for the latest edition of the standard. Here is a general methodology based on the 2016 version:

Methodology for Aggregate Gradation Test (IS 2386 Part 1: 2016)

Equipment and Materials:

  1. Sieve Set:
    • Standard sieves conforming to IS 460 (Part 1).
    • Sieve sizes: 80 mm, 40 mm, 20 mm, 10 mm, 4.75 mm, 2.36 mm, 1.18 mm, 600 µm, 300 µm, and 150 µm.
  2. Balances: A balance accurate to 0.1% of the weight of the test sample.
  3. Oven: Capable of maintaining a temperature of 100 to 110°C.
  4. Sample: The aggregate sample should be representative of the material to be tested.

Procedure:

  1. Preparation of Sample: The test sample is prepared by thoroughly mixing and reducing a representative portion of the aggregate to obtain a test sample.
  2. Sieve Analysis:
    • The prepared sample is sieved through the series of sieves mentioned above, starting from the coarsest sieve to the finest.
    • Weigh each fraction retained on the sieves.
  3. Calculations:
    • Calculate the cumulative percentage passing each sieve by dividing the sum of the weights of the material retained on all the finer sieves by the total sample weight.
    • Calculate the cumulative percentage retained on each sieve.
  4. Graphical Representation:
    • Plot the cumulative percentage passing against the sieve size to obtain the gradation curve.
    • Identify the percentage passing specific sieve sizes, such as D10, D30, D60, and D90.

Definitions:

  • D10, D30, D60, D90: These represent the particle sizes below which 10%, 30%, 60%, and 90%, respectively, of the aggregate particles are finer.

Reporting:

  • Report the results of the test, including the gradation curve and the percentage passing specific sieve sizes.

Example Aggregate Gradation Test

Equipment and Materials:

  1. Sieve Set: Standard sieves (80 mm, 40 mm, 20 mm, 10 mm, 4.75 mm, 2.36 mm, 1.18 mm, 600 µm, 300 µm, 150 µm).
  2. Balances: Precision balance.
  3. Oven: Set to 100-110°C.
  4. Sample: Representative aggregate sample.

Procedure:

  1. Preparation of Sample: A 2 kg sample is collected and oven-dried to constant weight.
  2. Sieve Analysis:
    • The dried sample is sieved using the specified sieves.
    • Weights of material retained on each sieve are recorded.
  3. Calculations:
    • Cumulative percentages passing and retained are calculated.
    • For example: If the weight retained on the 4.75 mm sieve is 300 g, and the total sample weight is 2000 g, then the cumulative percentage passing the 4.75 mm sieve is (2000 – 300) / 2000 * 100 = 85%.
  4. Graphical Representation: The cumulative percentages passing are plotted against the sieve sizes to create a gradation curve.

Reporting:

  • Graph:The gradation curve visually represents the distribution of particle sizes.
  • Specific Values:D10, D30, D60, D90 values are identified from the graph.
  • Report:A report includes the gradation curve and specific values, along with any other relevant information.

This is a basic example, and in a real-world scenario, the testing would involve more precise measurements and adherence to the standard procedures outlined in IS 2386 (Part 1): 2016. Always refer to the latest standard for accurate testing procedures and requirements.