Soundness test on aggregates as per IS: 2386 (Part-5)

[Srinivasan]

Soundness test on aggregates as per IS: 2386 (Part-5)

OBJECTIVE
To determine the soundness of aggregates

APPARATUS/REAGENTS

1. Sieves 80 to 4.75 mm for CA & 4.75 mm to 150 mic for FA
2. Temperature regulation
3. Containers
4. Balance
5. Oven
6. Sodium sulphate
7. Magnesium sulphate

THEORY
Soundness is the property of aggregate to resist disintegration when subjected to freezing and thawing. The test is intended to study the resistance of Aggregates to weathering condition in concrete or other applications. It is carried out to judge the durability of soundness of the Aggregate.
In order to quicken the effect of weathering due to alternate set-dry and or freeze-thaw cycles in the laboratory, the resistance to disintegration of aggregate is determined by soaking the aggregate specimen in saturated solution of sodium sulphate or magnesium sulphate.

PREPARATION OF REAGENT.
Saturated solution of sodium sulphate (the anhydrous Na2SO4 or the crystalline Na2SO4.10 H2O) is prepared in water at a temperature of 250 to 300C. It should be ensured that the solution is saturated and excess salt is present.
The solution is maintained at a temperature of 27° ± 2° C and stirred at frequent intervals until it is used. At the time of using the solution should have a specific gravity of not less than 1.151 and not greater than 1.171 and discolored solution should not be used.
It may be necessary to use not less than 420 gm of anhydrous salt or 1300 gm of the crystalline decahydrate salt per liter of water.
Alternatively saturated solution of magnesium sulphate may be prepared by dissolving either anhydrous (Mg SO4) or crystalline (Mg SO4. 7H2O) magnesium sulphate. At the time of using, the solution should have a specific gravity of not less than 1.295 and not more than 1.308. Not less than 400 gm of the anhydrous salt or 1600 gm of the crystalline hepta hydrate may be used per liter of water.

Coarse Aggregate:
The specimen of coarse aggregate for the test may be prepared after removing the fraction finer than 4.75 mm is sieve. The sample should be of such a size that it will yield not less than the following amounts of the different size which should be available in amounts of 5 % or more

Fine Aggregate
Fine aggregate for the test shall be passed through a 10 mm IS Sieve. The sample shall be of such a size that it will yield not less than 100 gm of each of the following sizes which shall be available in amount of 5 % or more, expressed in terms of the following sieves;

PROCEDURE

1. The sample of coarse aggregate should be thoroughly washed and dried to a constant weight at 105° to 110°C and is separated to different size ranges.
2. The proper weight of the sample for each fraction is weighed and placed in separate containers for the test. In the case of fraction coarser than 20 mm, the particles are also counted.
3. The samples are immersed in the prepared solution of sodium suplhate or magnesium sulphate for 16 to 18 hours in such a manner that the solution covers them to a depth of at least 15 mm.
4. The containers are kept covered to reduce evaporation and during the period of immersion, the temperature of the solution is maintained at 27°± 1°C.
5. After the immersion period, the aggregates are removed from the solution, drained for about 15 minutes and placed in the drying oven at 105° to 110°C.
6. The samples are dried to a constant weight at this temperature by checking the weights after 4 hours upto 18 hours.
7. When the successive weights differ by less than 1 g, it may be considered that constant weight has been attained and then it may be allowed to cool to room temperature. Then the aggregates are again immersed in the prepared solution, for the next cycle of immersion and drying. The number of cycles of alternate immersion and drying are minimum five (5) for road aggregates.
8. After completion of the final cycle, the sample is cooled washed free from the sulphate. This may be determined when there is no more reaction of the wash water with barium chloride (i.e. when there is no white precipitation when barium chloride is added to wash water it can be said that there is no sulphate with wash water).
9. Each fraction of the sample is then dried to constant temperature of 105° to 110°C and weighed. Coarse aggregate fractions are sieved by IS sieves of sizes indicated below:
10. Each fraction of aggregate is examined visually to see if there is any evidence of excessive splitting crumbling or disintegration of the grains. A combined sieve analysis of all the material subjected to the above test cycles may also be carried out to note the variation from the original grain size distribution of the sample.

Detailed procedure along with calculation is attached below.