Silt Content In Sand: Test, Procedure & IS Code Recommendation

Silt content in sand refers to the proportion of fine particles of silt (typically smaller than 75 microns) present in a sample of sand.

Silt is a type of sedimentary material that can be found in natural sand deposits, and it can affect the quality of sand used in construction.

High levels of silt content in the sand can reduce its strength, cohesion, and permeability, making it less suitable for use in certain types of construction projects. Testing for silt content in the sand is important to ensure that it meets industry standards and requirements, and to prevent potential issues that may arise during construction.

The permissible silt content in the sand must not exceed the values as specified in the IS standards. This methodology is only applicable to natural sand; it should not be used for crushed rock sand.

A good quality generally has a particle size between 150 microns to 4.75 mm sieve size and if the particle size in the sand is less than this size, it is known as silt in the sand.

If silt content in sand exceeds more than 8% that may result in a reduction in the binding capacity of mixed materials, and also affect the strength and durability of the final product.

IS Code for Silt Content Test of Sand: IS 2386-2 (1963)

Silt Content In Sand Limit

Silt content in the sand must not exceed 8% as per IS 2386-2. If the silt content on sand exceeds 8 % that may result in a reduction in the binding capacity of mixed materials, which also affects the strength and durability of the final product.

Silt Content Test

Apparatus

• 250 ml glass measuring cylinder
• Water
• Sand

Silt Content Test of Sand Procedure

• The measuring cylinder is filled with the salt-water solution (the concentration of the solution will be a teaspoon full of common salt for every 570 ml) up to the 50 ml mark on the cylinder.
• Add sand until the level of the sand is reached the 100 ml mark.
• Add further salt-water solution till the 150 ml mark is reached.
• Place the palm on the mouth of the glass cylinder and shake it vigorously.
• Place the measuring cylinder on a hard leveled surface and tap it all around so that the sand is leveled.
• Wait for three hours for the silt to settle on top of the sand.
• Measure the thickness of the silt layer and the height of the sand.

Observation Table

DETERMINATION OF SILT CONTENT

Silt content in sand (%) = [(Thickness of silt layer / Height of sand + Silt) x 100%]

If silt content is exceeding 3% by weight, then the washing of sand is necessary. After performing a few tests, a co-relation can be developed for silt layer thicknesses at various intervals of time. The silt content after a time interval of 10 minutes can be fixed as inspection criteria.

Sample Calculation

If the following observations are taken from the silt content of the sand test,

• Silt Layer Thickness = 1 cm
• Sand + Silt Layer Height or Thickness = 10 cm
• Silt Content of Sand = (1 cm / 10 cm) x 100 %
• Silt Content of Sand = 1%

So, from the above Test and calculations, we can say that this sand has a 1% silt content.

The silt content limit in the sand as per IS code is 8%, so this sand we can use this for construction purposes.

Watch Video: Silt Content of Sand Determination

Conclusion:

In conclusion, the determination of silt content in sand is a vital test for assessing sand quality in construction projects, excessive silt content can negatively impact the strength, workability and durability of concrete and mortar.

The test procedure involves collecting a representative sample, drying, washing sieving, and weighing the silt particles, the silt content is calculated as a percentage, the Indian Standards Institute(ISI) recommends the use of IS: 2386(part1)-1953 code for conducting the test.

Adhering to this code ensures standardized testing and accurate results.

By controlling the silt content within permissible limits, engineers can ensure the overall quality and performance of concrete and mortar structures, the silt content test, supported by the IS code recommendation, enables informed decision- making and helps maintain the integrity of construction projects.

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