DETERMINATION OF SPECIFIC GRAVITY AND WATER ABSORPTION OF COURSE AGGREGATE

Relevant IS code – IS: 2386 (Pt. – III) –1963

For aggregates larger than 10 mm & up to 40 mm:

A sample of aggregates not less than 2 kg is taken. 

It is thoroughly washed to remove the finer particles and dust adhering to the aggregate. 

It is then placed in a wire basket and immersed in distilled water at a temperature between 220 to 320 C. 

Immediately after immersion the entrapped air is 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 sec. 

During the operation, care is taken that the basket and aggregate remain completely immersed in water.

They are kept in water for a period of 24 + ½ hours afterwards. The basket and aggregate are then jolted and weighed (weight A1) in water at a temperature 220 to 320 C. 

the basket and the aggregate are then removed from water and allowed to drain for a few minutes and then the aggregate is taken out from the transferred to the second dry cloth and further dried. The empty basket is again immersed in water, jolted 25 times and weighed in water (weight A2). 

The aggregate is exposed to atmosphere away from direct sunlight for not less than 10 minutes until it appears completely surface dry. 

Then the aggregate is weighed in air (weight B). Then the aggregates is kept in the oven at a temperature of 100 to 1100C and maintained at this temperature of 24 + ½ hours. It is then cooled in the airtight container, and weighed (weight C).

\[Where,\]

\[ A = ~the ~weight ~in ~gram ~of ~the~ saturated \]

\[ aggregate~ in ~water ~(A1 – A2) \]

\[ B = ~the~ weight ~in~ grams ~of ~the ~saturated \]

\[ ~surface ~dry~ aggregate~ in ~air \]

\[ C =~the~ weight ~in~ grams~ of~ oven \]

\[ ~dried ~aggregate~ in ~air. \]

Water absorption:

Generally water absorption of coarse aggregate can be taken as 1% by weight of aggregate. The above described wire basket method can be adopted or in the field the following method can be adopted.

The method to check absorption is to take a sample of about 2 kg and to heat it up in oven. It will become bone dry. Its weight (W1) should be taken. Later this should be immersed in water for 24 hours. After that it should be taken and should be spread on a plate not exposed to sun and let it dry for 2 to 3 hours. Thus it gets air-dried. It weight (W2) should be taken. The difference between the weights gives the water absorption.

\[{Absorption ~ in~ \%  } = {{{W2 – W1  } \over {W1 }} {X 100} }\]