# MATERIAL TESTING Specific Gravity of Soils

### Specific Gravity of Soils

Standard AASHTO T 100-15 / ASTM D 854-00

The specific gravity of soils composed of particles smaller than the 4.75-mm (No. 4) sieve is determined by means of a pycnometer as per AASHTO T 100-15 test method. For soils with particles larger than the 4.75-mm (No. 4) sieve, the method outlined in AASHTO T 85 is followed.
Ii the soil is composed of particles both larger and smaller than the 4.75-mm (No. 4) sieve, the sample is first separated on the 4.75-mm (No. 4) sieve. AASHTO T 85 test procedure is adopted on the particles retained on 4.75-mm (No. 4) sieve and AASHTO T 84 for particles passing 4.75-mm (No. 4) sieve, and a weighted average is calculated.

Specific Gravity is defined as the ratio of the mass of a unit volume of a material at a stated temperature to the mass of the same volume of gas-free distilled or deionized water at a stated temperature.
The weighted average is calculated using the following formula; $G a v g = 1 R 1 100 G 1 + P 1 100 G 2$ where:
Gavg = weighted average specific gravity of soils composed of particles larger and smaller than the 4.75-mm (No. 4) sieve.
R1 = percent of soil particles retained on the 4.75 mm sieve.
P1 = percent of soil particles passing the 4.75 mm sieve.
G1 = apparent specific gravity of soil particles retained on the 4.75 mm sieve as determined by AASHTO T 85.
G2 = specific gravity of soil particles passing the 4.75 mm sieve as determined by AASHTO T 84.

## Pycnometer

Volumetric flask having a capacity of atleast 100 mL or a stoppered bottle having of atleast 50 mL.

## Drying Oven

Thermostatically controlled drying oven capable of maintaining a temperature of 110 ± 5°C (230 ± 9°F).

## Thermometer

Specific gravity test is carried out on either oven-dried soils or soils at its natural moisture content.
Either a volumetric flask or a stoppered bottle is used as pycnometer for conducting the tests.
At least 25 g of the oven-dry soil test sample is used when the volumetric flask is used and at least 10 g of the oven-dry soil test sample is used when stoppered bottle is used.
When the sample contains natural moisture, the mass of the oven-dried soil, W0 is determined at the end of the test by evaporating the water in an oven maintained at 110° ± 5°C (230 ± 9°F). When oven-dry samples are used, dry the sample for at least 12 h, or to constant mass, in an oven maintained at 110° ± 5°C (230 ± 9°F), cool it to room temperature, record its mass, and transfer it to the pycnometer.

Standardization of Pycnometer:

Step 1: Record the mass of dry pycnometer (Wf).

Step 2: Fill the pycnometer with distilled water and determine and record the mass of the pycnometer and water (Wa). Immediately, insert the thermometer into the water and determine its temperature Ti.

Calculation: To determine Wa at the desired temperature Tx;
Wa@Tx=(Density of water at Tx/Density of water at Ti) × (Wa@Ti - Wf) + Wf.

Test Procedure:

Step 1: Add distilled water io the prepared soil sample transferred to volumetric bottle/stoppered flask in such a way that the water will cover the soil to a maximum of about three-fourths full in the volumetric flask or about one half full in the stoppered bottle.

Step 2: Remove entrapped air by either boiling the pycnometer gently for atleast 10 minutes or by applying a partial vacuum of 13.33 kPa (100 mm Hg).

Step 2: Fill the pycnometer to its calibrated capacity. Clean the outside of the pycnometer with a dry cloth and determine the mass of pycnometer and its contents (Wb) and the temperature (Tx) of the contents.

Specific Gravity of soil based on water at temperature Tx is calculated as; where:
Tx=Temperature of the contents of the pycnometer when mass Wb was determined.
W0=Mass of oven dried soil sample in grams.
Wb = Mass of pycnometer filled with water and soil at temperature Tx.
Wa = Mass of pycnometer filled with water at temperature Tx (determined during the calibration of pycnometer).

AASHTO T 100 requires the specific gravity values to be reported based on water at 20°C. Specific Gravity of soil based on water at temperature 20°C is calculated as;
Specific Gravity @ 20°C = K × Specific Gravity @ Tx°C.
where;
K = ratio of relative density of water at Tx°C to the relative density of water at 20°C = ρw/0.99820
The following Density of water-Temperature correlation as provided in ASTM D 854 has been used to calculate the density of water, ρw (mg/litre) in this TransCalc tool.

$ρ w = 1.00034038 − ( 7.77 × 10 − 6 ) × T − ( 4.95 × 10 − 6 ) × T 2$
where:
T = the test temperature in °C.

SPECIFIC GRAVITY OF SOILS

Please enter the measured mass of pycnometer during the calibration of pycnometer.

Please enter the measured temperature of water during the calibration of pycnometer.

Please enter the mass of pycnometer and water during the calibration of pycnometer at calibration temperature (Ti).

Specific Gravity of Soils: Output

Test Temperature Tx:

Density of Water at Test Temperature Tx:

Density of Water at 20 °C:

Specific Gravity of Soils at Temperature Tx:

Specific Gravity of Soils @ 20°C:

Weighted Average Specific Gravity

Specific Gravity Mass Percentage

Weighted Average Specific Gravity

Weighted Average Specific Gravity:

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