Determination of Specific Gravity and Water Absorption of Course Aggregate

The coarse aggregate specific gravity test is used to calculate the specific gravity of a coarse aggregate sample by determining the ratio of the weight of a given volume of aggregate to the weight of an equal volume of water.

AIM:

To determine specific gravity of a given sample of course aggregate.

Apparatus:

·         Wire basket

·         Watertight container

·         Well-ventilated oven

·         Airtight container

·         Balance

FIGURE:

 

Procedure:

1.   A sample of not less than 2000 g of the aggregate shall be thoroughly washed to remove finer particles and dust, drained and then placed in the wire basket and immersed in distilled water at a temperature between 22°C to 32°C with a cover of at least 5 cm of water above the top of the basket.

2.   Immediately. after immersion the entrapped air shall be removed from the sample by lifting the basket containing it 25 mm above the base of the tank and allowing it to drop 25 times at the rate of about one drop per second. The basket and aggregate shall remain completely immersed during the operation and for a period of 24 ± 1/2 hours afterwards.

3.   The basket and the sample shall then be jolted and weighed in water at a temperature of 22°C to 32°C (weight A1).

4.   The basket and the aggregate shall then be removed from the water and allowed to drain for a few minutes, after which the, aggregate shall be gently emptied from the basket on to one of the dry clothes, and the empty basket shall be returned to the water and weighed in water (weight A2).

5.   The aggregate placed on the dry cloth shall be gently surface dried with the cloth, transferring it to the second dry cloth when the first will remove no further moisture. The aggregate shall then be weighed (weight B).

6.   The aggregate shall then be placed in the oven in the shallow tray, at a temperature of 100 to 110°C and maintained at this temperature for 24 ± 1/2 hours. It shall then be removed from the oven, cooled in the airtight container and weighed (weight C).

Calculations:

Specific gravity, apparent specific gravity and water absorption shall be calculated as follows: 

Specific Gravity =C/(A-B)

Apparent specific Gravity =C/(C-B)

Water Absorption =(100(B-C))/B

A = Weight of saturated aggregate in water = (A1-A2)

B = Weight of the saturated surface-dry aggregate in air.

C = Weight of oven-dried aggregate in air.

A1=Weight of aggregate and basket in water.

A2=Weight of empty basket in water.

Conclusion / Result :

i) The Specific Gravity of a given sample of course aggregate is found to be …….
ii) The Water Absorption of a given sample of course aggregate is found to be ……. %