How to Find specific gravity of coarse aggregate


specific gravity of coarse aggregate  



Apparatus and materials

1.      Spring balance

2.      Weight balance

3.      Coarse aggregate of weight 2kg

4.      Bucket
                     
5.      Water tank

6.      Oven



Procedure


1.      Aggregate not less than 2 kg was taken. It was carefully washed to eliminate the finer particles and dust.

2.      It was then positioned in a wire basket and deep in distilled water at a temperature between 22° to 32°C.
3.      Immediately after absorption, the entrapped air was removed from the sample by lifting the basket it 25 mm above the base of the tank and allowing it to drop 25 times at the rate of about one drop per sec. During the operation, caution was taken that the basket and aggregate remain completely immersed in water.




4.      They were kept in water for a period of 24 ± 1/2 hours afterwards.

5.      The basket and aggregate were then jolted and weighed (weight A1) in water at a temperature 22° to 32° C.

6.  The basket and the aggregate were then removed from water and allowed to drain for a few minutes and then the aggregate was taken out from the basket and placed on dry cloth and the surface was gently dried with the cloth. The aggregate was transferred to the second dry cloth and further dried.

7.  The empty basket was again immersed in water, jolted 25 times and weighed in water (weight A2).

8.  The aggregate was exposed to atmosphere away from direct sunlight for not less than 10 minutes until it appears completely surface dry. Then the aggregate were weighed in air (weight B).

9.  Then the aggregate were kept in the oven at a temperature of 100 to 110°C and maintained at this temperature for 24 ± 1/2 hours. It was then cooled in the air-tight container, and weighed (weight C).
A= the weight in gm of the saturated aggregate in water (A1 – A2),

B = the weight in gm of the saturated surface-dry aggregate in air, and

C = the weight in gm of oven-dried aggregate in air.

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