Silt Content Test of Sand (Fine Aggregates)

AIM

To find-out the silt content in sand (fine aggregates)

Apparatus

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Measuring cylinder
  1. Measuring cylinder – 250ml
  2. Sand  – Specimen
  3. Water
  4. Salt Solution

Procedure

  • The measuring cylinder should be free from moisture and dry.
  • Fill the water up to 50 ml with 1% salt solution.
  • Then add sand to it until the level reaches 100 ml. 
  • Again add salt solution up to the level of 150 ml.
  • Close the mouth of the cylinder and shake well then keep the cylinder on a flat surface.
  • The silt content shall be settled over the sand layer after 2 hours.
  • Now note down the silt layer alone volume as V1 ml (settled over the sand)
  • Then note down the sand volume (below the silt) as V2 ml
  • Repeat the procedure two more times to get the average.

How to calculate the percentage of Silt?

  1. V1 = Volume of Silt layer (Silt settled over the sand layer).
  2. V2 = Volume of the Sand layer (which is settled under the silt).

Percentage of Silt = (V1/V2) x 100

The permissible Silt content in sand percentage is only 6%.

Report/Observation Table 

S.NO DESCRIPTION SAMPLE NO
SAMPLE 1 SAMPLE 2 SAMPLE 3
1 Volume of Sample (V1) ml
2 Volume of Silt (V2) ml
3 Percentage of Silt (V2/V1) x 100
Average 

Technical Discussion

Effect of Silt fines on concrete properties:
  • Increase in water/cement ratio result to a decrease in the compressive strength of concrete 
  • The increase in sand fines content has also been found to decrease the compressive and tensile strengths of concrete
  • Inadequate sand fine content also has adverse effect of the strength of concrete due to poor adhesion
  • The decrease in slump value as a result of increase in fines percentage in sand can be attributed to the fact that finer particles have larger surface area which absorbs more water in concrete mix.
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