STANDARD
- IS: 2720 (Part 3/Sec-1) 1980.
DEFINITION
- Specific gravity is defined as the ratio of the mass of a given volume of the substance to the mass of an equal volume of water.
APPARATUS
- Density Bottles (Pycnometer) of approximately 50m1 capacity with stopper.
- Thermostatically controlled water bath maintained with in 27 ± 0.2°C.
- Thermostatically controlled oven of capacity 250°C.
- Analytical balance of sensitivity 0.00l gram.
- 2 mm IS sieve.
- Vacuum pump.
- A wash bottle preferably made of plastics.
- Riffle box.
- A length of rubber tubing to fit the vacuum pump.
PROCEDURE
- Dry the pycnometer in the oven at a temperature of 105 to 110°C and cool it and weigh (m1)
- Take approximately 5 to 10 gram from 50 gram of oven dried soil sample obtained by riffling and well pulverized to pass 2 mm IS sieve if necessary.
- Transfer the cooled soil sample in to the pycnometer.
- Weigh the pycnometer and the soil sample together with the stopper (m2).
- Add sufficient air free distilled water in to the pycnometer so that the soil in the bottle is just covered.
- Carefully stir the soil in the pycnometer with a stirrer.
- Wash out all the particles of soil that adhering to the stirrer with a few drops of air free liquid.
- Transfer the pycnometer in to the constant temperature bath maintained within 27 ± 0.2°C and immersed up to the neck of the bottle.
- Allow the pycnometer to remain in the constant temperature bath for approximately about one hour or until it has attained the constant temperature of the bath.
- Remove the pycnometer from the water bath wipe it dry and weight (m3) .
- Clean the pycnometer and fill it with air free liquid, replace the stopper and keep it in the constant temperature bath for approximately about one hour or until it attains the constant temperature of the bath and weigh (m4).
- Make at least two determinations for each test.
CALCULATIONS
- If distilled water is used as an air free liquid, calculate the specific gravity of the soil particles ‘G’ from the equation
m2— m1
G= ———————-
(m4-m1)-(m3—m2)
G= Specific gravity of the liquid used at the constant temperature.
m1= mass of pycnometer.
m2 = mass of pycnometer + dry soil.
m3 = mass of pycnometer, soil and water.
rn4 = mass of pycnometer and water.
REPORT
- Report the individual and the mean results to the nearest 0.01 at 27°C.
- If the two results differ by more than 0.03 repeat the test.
PRECAUTIONS
- Soil should not be dried more than 80°C if there is any doubt in change of specific gravity by oven drying due to loss of water during hydration.
- It has been observed that largest source of error in the test is due to the difficulty in ensuring the complete removal of air from the sample.
- To obtain reliable and quicker results the soil should be left under vacuum for several hours, preferably overnight shaking the bottle in hand once or twice interrupting the vacuum.
DETERMINATION OF SPECIFIC GRAVITY
IS:2720 (Part 3/Section 1)1980
| Description | Units | Test I | Test 2 |
| Weight of the Pycnometer with lid (m1) |
gm |
||
| Weight of the Pycnometer + soil (m2) |
gm |
||
| Weight of Pycnometer + soil + water (m3) |
gm |
||
| Weight of Pycnometer filled with water (m4) |
gm |
||
| ( m2—m1) Specific gravity G= —————————— ( m4—m1 )—(m3—m2) |
– | ||
| Average Specific gravity | . | ||
| Remarks: | |||