Specific Gravity and Water Absorption Test of Coarse Aggregate | Specific Gravity of Coarse Aggregate

Specific gravity and Water Absorption Test of Aggregates are major important tests to be performed on aggregate.

These two parameters or properties of aggregate play an important role in the mix design of concrete.

As we know that aggregate occupies 70 to 80% volume of concrete, and its testing becomes essential before use.

As per IS: 2386 (Part III) – 1963 –  (Indian Standard- Methods of Test for Aggregates for Concrete – Specific Gravity, Density, Voids, Absorption, and Bulking),

Specific Gravity and Water Absorption Test of Coarse Aggregate

Specific Gravity and Water Absorption Test of Coarse Aggregate are two important tests of coarse aggregate used in construction. Let’s discuss them in detail,

Specific Gravity

“Specific Gravity is defined as the ratio of the weight of a given volume of aggregate to the weight of an equal volume of water.”

The specific gravity usually showed the strength and quality of the material. The specific gravity of aggregates test is usually used for the identification of stones or aggregates.

Aggregates with low specific gravity values are mostly weaker than those with higher specific gravity values.

Water Absorption

Water absorption of aggregates is the % of water absorbed by an air-dried aggregate when immersed in water at 27°C for a period of 24 hours. 

Significance of Water Absorption Test On Aggregates

The water absorption test uses to find the water-holding capacity of the aggregates.

The water is absorbed by the aggregates or stones in their pores known as water absorption. Usually, water absorption gives an idea about the strength of the aggregates.

That aggregate has more water absorption and is usually unsuitable for construction.

There is a basic 3 methods specified to find out the specific gravity of aggregates based on their sizes.

1. The aggregates are larger than the 10mm (Basket method)
2. The aggregates are between 10mm and 40mm (Basket method)
3. The aggregates are smaller than 10mm (Pycnometer bottle)

Read More: Flakiness and Elongation Index Test of Coarse Aggregate

Objectives of Specific Gravity and Water Absorption Test

To Determine the Specific Gravity and Water Absorption Value of the Aggregate Sample.

Reference:- Specific Gravity of Fine Aggregate as per IS Code 2386 (Part 3) – 1963 PDF

Reference: water absorption test for coarse aggregate is code 2386 (Part 3) – 1963 PDF

Apparatus

1. Balance

The balance used to measure the aggregate has sufficient capacity (3kg minimum). Accuracy of balance readable up to 0.5gm.

The balance is such a type and its shape also permits the basket containing the sample to be hung from the beam and weight in water.

2. Oven

The oven used for the test is well-ventilated or thermostatically controlled to maintain the temperature of the oven up to 100*C to 110*C.

3. Wire Basket

The wire basket used for the test is not more than 6.3mm mesh or it is also a perforated container of convenient size.

• It is usually chromium-plated and well-polished.
• It has wire hangers that are not thicker than 1mm for hanging it from the balance.
• A basket has freely hanged this type of watertight container is used.
• Dry and soft absorbent clothes are used. (2nos.). Min. size of the clothes is 75*45cm.
• A tray is used for test Min. an area not less than 650cm^2.
• An airtight container is also used. The capacity o container is similar to the basket.

Specific Gravity and Water Absorption Test of Aggregates

Following the procedure used for specific gravity and water absorption test of aggregate,

1. Take about 2 kg of an aggregate sample (Aggregate which has been artificially heated shall not be used).

2. The aggregates are thoroughly washed so, the finer particles of the dust are removed from their surface.

3. Then the washed aggregates are placed in the wire basket and immersed in the distilled water at a temperature between 22° C to 32° C with a cover from the water surface of at least 5 cm on top of the basket.

4. The basket immersed in the water requires immediate removal of entrapped air. This entrapped air was removed by lifting the basket 25 mm above the base of the tank and allowing 25 drops at the rate of about 1 drop/sec. Then basket filled with aggregate is allowed to be immersed in water for a period of 24 hrs.

5. After 24 hours the basket and the aggregates are weighed in the water at a temperature of 22° C to 32° C. (W1)

6. Then the basket and the aggregates are taken out from the water and allowed to drain for a couple of minutes after these aggregates are removed from the basket and placed on the dry cloths.

 7. After this the empty basket is again immersed in the water, apply 25 drops, and weighed in water. (W2)

8. The aggregates are placed on the dry cloth and are gently surface dried with a cloth if 1st cloth is not taken moisture then aggregates are transferred to the second one.

After these aggregates are spread on the cloth and less exposed to the atmosphere away from direct sunlight or also away from another source of heat until it appears to be completely surface dried.

10. For accelerating the unheated air may be used after the first 10 minutes for those aggregates which are difficult to dry and weigh it. (W3)

11. Then the aggregates are placed in the shallow tray and put in the oven at a temperature of 100° C to 110° C for 24 hours.

12. After 24 hours the aggregates are removed from the oven and filled in the airtight container for the cooling of it and weighed. (W4)

Read More: You can download the IS Codes of Aggregates for FREE Here: IS: 2386 (Part I-VII) PDF

Observations

Weight of saturated aggregate sample suspended in wire basket = W1

Weight of basket suspended in water = W2

Weight of saturating aggregate in water = (W1-W2) = Ws

Weight of surface dry aggregate in air = W3

Weight of water equal volume of aggregate = (W3 – Ws)

Calculation

Specific Gravity of Aggregate = Dry Wt. Of Aggregate / Wt. Of Equal Volume Water

                                                    = W4 / (W3- Ws)

Apparent Specific Gravity = Dry. Wt. of Aggregate / Wt. Of the equal volume of water excluding air

                                             = W4 / (W4-Ws)

Water Absorption of Aggregate = %  by weight of  water absorbed  in terms of oven-dried  weight of aggregate

                                           = (W3 – W4) x 100) / W4

Specific gravity and water absorption of a coarse aggregate lab report are prepared after calculating the above values.

IS Reccomanded Values

The specific gravity of coarse aggregate as per its code is 2.5 to 3.

The water absorption of aggregate ranges from  0.1 to 2%.

Conclusion

In conclusion the specific gravity of coarse aggregate and water absorption tests are crucial in assessing the quality and suitability of aggregate for use in construction projects.

The specific gravity of coarse aggregate determines its density and weight to volume ratio, which can impact the overall strength and durability of concrete or asphalt mixtures and it provides valuable information for proportioning and designing concrete mixes as well as evaluating the potential for segregation and bleeding.

On the other hand, the water absorption test measure the amount of water absorbed by the coarse aggregate, indicating its porosity and ability to resist moisture.

Excessive water absorption can lead to reduced workability, increased shrinkage, and decreased durability of the concrete, this test helps in selecting aggregates with appropriate absorption characteristics to ensure long term performance and resistance to weathering effects.

Both tests are typically conducted according to standardized procedures and specification ensuring consistency and comparability of result.

The specific gravity and water absorption values obtained from this tests assist engineers, contractors and suppliers in making information decision regarding aggregate selection proportioning and mix design.

By evaluating the specific gravity and water absorption of coarse aggregates, construction professionals can optimize the performance of concrete mixes, enhance the durability of structure and mitigate potential issues related to moisture content and segregation.

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