TM-79, Procedure to Prepare Aggregate to Determine the Plasticity Index

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This test method prepares Minus No. 40 materials to determine the plasticity index. Apparatus

1) No. 40 (425μm) sieve

2) Miscellaneous containers and pans with lids – for washing, drying and storing.

3) Mortar and pestle.

4) Oven or other improvised drying unit capable of maintaining a temperature of less than 140° F (60° C). Procedure

1) Obtain a representative sample of 30 to 40 pounds (15 to 20 kg) in the “as received” or “as obtained” condition.

2) Reduce the sample to 500 – 2500 grams, depending on the maximum size of the material.

3) Sieve the sample over a No. 40 (425μm) sieve and save both fractions. Save the minus No. 40 material as part (a).

4) Place the sieve with the plus No. 40 (425μm) portion in a pan, cover with water and scrub the material between the hands, breaking up all lumps.

5) Wash the material on the No. 40 (425μm0 sieve until the water is clear, retaining the water and material washed through.

6) The plus No. 40 (425μm) material should be dried sufficiently to allow the minus No. 40 (425μm) particles to be removed by sieving, with care being taken to avoid splattering and loss of material from the sample. Retain all minus No. 40 (425μm) material after sieving and save as part (b).

7) All of the minus No. 40 [425μm] material that was washed from the coarse portion is allowed to settle out. Most of the liquid may then be siphoned off after one or two hours, depending on the type of material being tested. It is suggested that a small quantity of vinegar (a bottle-cap full should be sufficient) be added to the water to reduce surface tension and aid settlement of particles.

8) The remaining material should be dried in an oven, sand bath, or improvised drying unit with a maximum temperature of 140 degrees F. Care should be taken to prevent splattering and loss of material from the pan. Care shall also be taken to clean the pan thoroughly so that all material will be recovered. Break the material down to pass a No. 40 (425μm) sieve using mortar and pestle. Sieve over a No. 40 (425μm0 sieve and save minus No. 40 material as part (c).

9) Combine all three parts (a), (b), and (c) of minus No. 40 (425μm) material, mix thoroughly and select a sample for test.