Objective

For determination of specific gravity & water absorption of aggregates. 

Reference Standards

IS : 2386 (Part 3) – 1963 – Method of test for aggregates for concrete (Part I) Particle size and shape.

Equipment & Apparatus

• Wire basket
• Oven (300⁰c)
• Container for filling water and suspending the basket
• An air tight container
• Balance[0-10 kg]
• Shallow tray & absorbent clothes. 

Preparation of sample

The sample to be tested is separated from the bulk by quartering or by using sample divider.

Procedure

1. About 2kg of  the aggregate sample is washed thoroughly to remove fines, drained and then placed in the wire basket and immersed in distilled water at a temperature between 22 to 32⁰C with a cover of at least 50 mm of water  above the top of the basket
2. Immediately after the 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 second. The basket and the aggregate should remain completely immersed in water for a period of 24±0.5 hours afterwards.
3. The basket and the sample are then weighed while suspended in water at a temperature of 22 to 32⁰C. The weight is noted while suspended in water (W₁) g.
4. The basket and the aggregate are then removed from water and allowed to drain for a few minutes, after which the aggregates are transferred to one of the dry absorbent clothes.
5. The empty basket is then returned to the tank of water, jolted 25 times and weights in water (W₂) g.
6. The aggregates placed in the dry absorbent clothes are surface dried till no further moisture could be removed by this clothe.
7. Then the aggregate is transferred to the second dry cloth spread in a single layer, covered and allowed to dry for at least 10 minutes until the aggregates are completely surface dry. 10 to 60 minutes drying may be needed. The surface dried aggregate is then weighed W₃ g.
8. The aggregate is placed in a shallow tray and kept in an oven maintained at a temperature of 110⁰C for 24 hours. It is then removed from the oven, cooled in air tight container and weighed W₄ g. 

Calculation

Weight of saturated aggregate suspended in water with basket = W₁ g

Weight of basket suspended in water = W₂ g

Weight of saturated aggregate in water = (W₁-W₂)g = W_s g

Weight of saturated surface dry aggregate in air = W₄ g

Weight of water equal to the volume of the aggregate = (W₃-W_s) g

 Safety & Precautions

• Use hand gloves while removing containers from oven after switching off the oven.
• Thoroughly clean & dry the container before testing.
• Special care should be taken that no outer air enters when using the balance.
• Use apron & safety shoes at the time of testing.
• All parts of the equipment should always be kept clean.