Objective
To determine the approximate percentage of light weight pieces (i.e. coal & lignite) in aggregate by means of sink-float separation in a heavy liquid of suitable specific gravity.
Apparatus
| Name | Capacity | Least Count |
| Balance | 500 g | 0.1 g |
| Balance | 5000 g | 1 g |
| Oven | 100 to 1100C | |
| Sieve | 300 micron, 4.75 mm | |
| Container | As per requirement | |
| Skimmer | Having 300 micron sieve cloth |
Heavy Liquid
Bromotrichloromethane having specific gravity of 2.00
(a) Procedure For Fine Aggregate
- Take minimum of 200 g of sample and dry it in an oven till it attains a constant mass.
- After drying the sample, cool it to room temperature and sieve it through a 300 micron sieve until all the material finer than 300 micron get separated.
- Weigh the material retained on the 300 micron sieve to the nearest 0.1 g.
- Take heavy liquid (Bromotrichloromethane) in a container of suitable volume. (The volume of heavy liquid to be taken being at least three times the absolute volume of aggregate)
- Introduce all the material coarser than 300 micron into this heavy liquid and stir it gently.
- Pour the liquid off into a second container, passing it through the skimmer and taking care that only the floating pieces are poured off with the liquid and that non of the sand is decanted onto the skimmer.
- The liquid which has been collected in the second container is again poured into the first container. Agitate the remaining sample by stirring and repeat the decantation process as described in step-6, until the sample is free of floating pieces.
- Wash the decanted pieces contained on the skimmer in carbon tetrachloride to remove heavy liquid, and then dry it.
- Weigh the decanted pieces to the nearest 0.1 g.
Calculation
Calculate the percentage of light weight (pieces floating on heavy liquid) as follows
L = (W1/W2)*100
Where,
L = percentage of light weight pieces
W1 = dry weight in g of decanted pieces
W2 = dry weight in g of portion of sample coarser than 300 micron IS sieve.
(b) Procedure For Coarse Aggregate
- Take minimum of 2000 g of sample and dry it in an oven till it attains a constant mass.
- After drying the sample, cool it to room temperature and sieve it through a 4.75 mm sieve until all the material finer than 4.75 mm get separated.
- Weigh the material retained on the 4.75 mm sieve to the nearest 1 g.
- Take heavy liquid (Bromotrichloromethane) in a container of suitable volume. (The volume of heavy liquid to be taken being at least three times the absolute volume of aggregate)
- Introduce all the material coarser than 4.75 mm into this heavy liquid and stir it gently.
- Using skimmer remove the pieces that rise to the surface, and save them.
- Repeatedly agitate the remaining pieces and remove the floating pieces until no additional pieces rise to the surface.
- Wash the decanted pieces in carbon tetrachloride until all of the heavy liquid is removed, and allow it to dry.
- Weigh the decanted pieces to the nearest on gram.
Calculation
Calculate the percentage of light weight (pieces floating on heavy liquid) as follows
L = (W1/W2)*100
Where,
L = percentage of light weight pieces
W1 = dry weight in g of decanted pieces
W2 = dry weight in g of portion of sample coarser than 4.75 mm IS sieve.
Report
The percentage of light weight pieces (coal & lignite) in the aggregate is reported to the nearest 0.1 percent.
Precautions
- Chemicals used in this test are highly toxic, both by absorption through the skin and by inhalation.
- While testing, use a hood and care shall be taken to avoid contact with the skin or inhalation of fumes.
Reference
- IS:2386 (Part-2) – Methods of test for aggregates for concrete (Part-2 – Estimation of deleterious materials and organic impurities)