4. Specific Gravity of the Soil

Specific Gravity (Standard Test Method for Relative Density and Absorption of Fine Aggregate) I.

Statement of Problem Purpose 

To determine the specific gravity of the soil. The specific gravity may be expressed as bulk specific gravity, bulk specific gravity SSD (Saturated-Surface Dry), or Apparent Specific Gravity.

Significance and Use 

Bulk specific gravity is generally used for calculation of the volume occupied by the aggregate on various mixtures containing aggregate, including Portland cement concrete, bituminous concrete, and other mixtures that are proportioned or analyzed on an absolute volume basis. Bulk specific gravity SSD is used to determine the surface moisture on fine aggregates. Apparent density pertain to the solid making up the constituent particles not including pore space within the particles which is accessible to the water. Lastly, absorption values are used to calculate the change in the mass of an aggregate due to water absorbed in the pore spaces within the constituent particles, compared to the dry condition.

ASTM Designation ASTM C128 – Standard Test Method for Relative Density (Specific Gravity) and Absorption of Fine Aggregate II.

Apparatus 1. Balance—A balance or scale having a capacity of 1 kg or more, sensitive to 0.1 g or less, and accurate within 0.1 % of the test load at any point within the range of use for this test method. Within any 100-g range of test load, a difference between readings shall be accurate within 0.1 g. 2. Pycnometer (for Use with Gravimetric Procedure)—A flask or other suitable container into which the fine aggregate test sample can be readily introduced and in which the volume content can be reproduced within 6 0.1 cm3. The volume of the container filled to mark shall be at least 50 % greater than C 128 – 01e12 the space required to accommodate the test sample. A volumetric flask of 500-cm3 capacity or a fruit jar fitted with a pycnometer top is satisfactory for a 500-g test sample of most fine aggregates. 3. Flask (for Use with Volumetric Procedure)—A LeChatelier flask as described in Test Method C 188 is satisfactory for an approximately 55-g test sample.

4. Mold and Tamper for Surface Moisture Test—The metal mold shall be in the form of a frustum of a cone with dimensions as follows: 40 6 3-mm inside diameter at the top, 906 3-mm inside diameter at the bottom, and 75 6 3 mm in height, with the metal having a minimum thickness of 0.8 mm. The metal tamper shall have a mass of 340 6 15 g and a flat circular tamping face 25 6 3 mm in diameter. Test Specimen The soil sample was obtained in accordance with ASTM D854. The sample should be thoroughly mixed and reduced to obtain a test specimen of approximately 100 (+ or -) 10 grams. III.

Test Procedure 1. Subsequently immerse the dry aggregate in water in at room temperature for a period of 24 (+ or -) 4 hours. 2. Decant excess water with care to avoid loss of soil, spread the sample on a flat nonabsorbent surface exposed to a gently moving current of warm air, and stir frequently secure homogenous drying. 3. Continue drying with constant stirring and test at frequent interval until the test indicates the specimen has reach a surface-dry condition. 4. For test for surface moisture, hold the mold firmly on a smooth nonabsorbent surface with the large diameter down. 5. Place a portion of the partially dried aggregate loosely in the mold by filling it to overflowing and heaping additional material above the top of the mold by holding it with the cupped fingers of the hand holding the mold. 6. Lightly tamp the fine aggregate into the mold with 25 light drops of the tamper. 7. Remove loose sand from the base and lift the mold vertically. If surface moisture is still present, the fine aggregate will retain the molded shape. Slight slumping of the molded fine aggregate indicates that it has reached a surface-dry condition. 8. Test the specimen by gravimetric procedure: 8.1. Partially fill the pycnometer with water. Introduce into the pycnometer 500 (+ or -) 10 grams of SSD fine aggregate, and fill with additional water to approximately 90% of capacity. 8.2. Manually roll, invert, and agitate the pycnometer to eliminate air bubbles. 8.3. After eliminating all air bubbles, adjust the temperature of the pycnometer and its contents to 232 if necessary by partial immersion in circulating water, and bring the water level by partial pycnometer to its calibrated capacity. 8.4. Determine the total mass of the pycnometer, specimen, and water. 8.5. Remove the fine aggregate from pycnometer, dry to constant mass at a temperature of 100 ± 5, cool in air at room temperature for 1 ± ½ hour and determine the mass. 8.6. Determine the mass of the pycnometer filled to its calibrated capacity with water 23 ± 2.

IV.

Computations Weight of pycnometer - 170 g Weight of beaker - 240 g Weight of beaker + soil sample - 346 g Weight of soil sample - 106 g Weight of pycnometer and water - 665 g Weight of water - 495 g Weight of pycnometer + water + sand - 726 g Saturated Surface Dry Soil - 112 g ITEM

MASS (g)

SYMBOL

Oven-Dry Specimen

98

A

Pycnometer with Water

665

B

Pycnometer with Water and Specimen

726

C

Saturated Surface-Dry Specimen

112

S

A. Bulk Specific Gravity

A 98 = = 1.92 665  112  726 B  S C

=

B. Bulk Specific Gravity (SSD) = C. Apparent Specific Gravity

D. Absorption V.

=

=

S 112  B  S  C 665  112  726

A 98  = 2.65 B  A  C 665  98  726

 S  A  112  98  100   100  A  98   

Summary of Results Bulk Specific Gravity

1.92

Bulk Specific Gravity (SSD)

2.12

Apparent Specific Gravity

2.65

Absorption

14.29 %

VI. Discussion on Findings

= 2.12

= 14.29％

The specific gravity of soil is an important parameter that is used together with other soil parameters (such as void ratio and degree of saturation) to compute additional useful information. It may be expressed as Bulk Specific Gravity, Bulk Specific Gravity SSD (Saturated-Surface Dry), or Apparent Specific Gravity. And based on ASTM D 854 Table 6-3, we conclude that the soil sample (s.g. = 2.65) is "Sand", having an Apparent Specific Gravity ranging from 2.65 - 2.67.