Determination of Plastic limit Test IS 2720 Part 5

(IS: 2720 – Part V) Apparatus 1. Porcelain evaporating dish. 2. Glass plate. 3. Spatula. 4. Moisture containers. 5. Rod of 3 mm dia. 6. Balance sensitive to 0.01 gm. 7. Oven, controlled at temperature of 1050C to 1100C. Soil Sample A sample weighing about 20 gm from thoroughly mixed portion of the material passing 425 micron IS sieve. Procedure 1. About 20 gm of dry pulverized soil passing 425 micron sieve is weighed. 2. The soil is mixed thoroughly with distilled water in the evaporating dish till the soil paste is plastic enough to be easily molded with fingers. 3. A small ball is formed with the fingers and this is rolled between the fingers and the glass plate to a thread. 4. Rate of rolling should be between 80 to 90 strokes/minutes counting a stroke as one complete motion of hand forward and back to the starting position again. 5. The rolling is done till the diameter of thread is 3 mm. 6. By trial, the thread that starts crumbling at 3 mm dia under normal rolling should be obtained and this should be immediately transferred to moisture container. 7. The above process is repeated to get at least three consistent values of the moisture content. 8. The moisture content determined as above is the Plastic Limit (WP) of soil. Calculation of Plasticity Index: Plasticity Index (%) = Liquid Limit (WL) – Plastic Limit (WP)