SPECIFIC GRAVITY AND WATER ABSORPTION OF AGGREGATE BY WIRE BASKET METHOD

Method of specific gravity and water absorption of coarse aggregate by wire basket method (Buoyancy Balance method). Specific gravity test of aggregates is done to measure the quality of the aggregates and the water absorption test determines the water holding capacity of the coarse and fine aggregate.

Test Standard : IS 2386-Part III: 1963

Test Apparatus :

• Weighing Balance
• Wire basket of mesh size not more than 6.3mm
• Water tank mounted on a platform and Mechanical lifting device used to raise the water tank through the frame height immersing the specimen suspended below the balance (Buoyancy Balance).
• Hot air oven of temperature range 100-110 °C
• Dry soft absorbent cloths.

Test procedure :

1. Sieve the aggregate from 6.3 mm sieve and Take about 2.0 kg retained sample. Wash the sample and remove all fine particles of dust,
2. Place the sample in wire basket & immerse in distilled water at a temperature between 22 °C to 32°C with a cover of at least 5.0 cm of water above the top of the bucket.
3. After immersion, the entrapped air shall be removed from the sample by lifting the basket 25 mm above the base of the tank and drop 25 times at the rate of one drop per sec.
4. The basket and the aggregate sample shall remain completely immersed during the operation and for a period of 24± ½ hours.
5. Record the weight of both the sample and the basket is to be immersed in water at the temperature between 22 °C to 32°C, say A1 gms.
6. The basket and the aggregate remove from the water and allowed to drain for few minutes, after draining out water, dry aggregate by dry cloth, and the emptied basket shall be returned to the water, jolted 25 times and weighed in water, say A2, gms. Weight the surface dried aggregate,say B, gms.
7. The aggregate shall then be placed in a hot air oven at a temperature of 100 °C to 110°C for a period of 24± ½ hours.
8. After 24± ½ hours remove the sample from the oven and cooled in a airtight container and weighed, say C, gms

Calculation of Specific gravity & water absorption

Specific gravity= {C/[B-A]}
Apparent specific gravity= {C/[C-A]}
Water absorption (%)= {(B-C)/C}x100
Where A= A1-A2 (Weight in gms of the saturated aggregate in water)

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