MET-HODS OF TEST FOR DETERMINATION OF WATER SOLUBLE CHLORIDES IN CONCRETE ADMIXTURES
This standard specifies the following methods of test for determination
of water soluble chlorides in concrete admixtures:
a) Volumetric method,
b) Gravimetric method, and
c) Turbidimetric method.
SELECTION OF METHOD
2.0 One of the three methods may be used appropriately depending on
the concentration of the chlorides in the admixtures as per the declaration
of the manufacturer.
2.1 The volumetric method may be used when the chloride concentration
is nearly 1 percent or above.
2.2 The gravimetric method may be used when the chloride concentration
is more than 2’5 percent.
2.3 The turbidimetric method may be used when the concentration of
chloride is as low as 2 ppm and above.
2.4 Where a choice is open between volumetric and gravimetric methods
volumetric method is preferable as it is quicker and less laborious.
Turbidimetric method may be adopted when the chloride concentration
is very low.
VOLUMETRIC METHOD
3.1 Reagents
3.1.0 Qgality of Reagents-Unless otherwise specified, pure chemicals
and distilled water (see IS: 1070-1960*) shall be employed in the tests.
NOTE - ‘ Pure chemicals ’ shall mean chemicals that do not contain impurities
which affect the results of analysis.
3.1.1 .Nitric Acid - 1 : 2.5 - 6 N.
3.1.2 Sodium or Potassium Chloride Solution ( Standard) -- 0.1 N.
3.1.3 Potassium Chromate Indicator Solution
3.1.4 Silver Nitrate Solution - 0’ 1 N.
3.1.4.1 Preparation -Weigh about 8.5 g of silver nitrate, dissolve in
distilled water and make up to 500 ml in a volumetric flask. 3.1.4.2 Standardization- Standardize the solution against 0.1 N
sodium chloride or potassium chloride solution using potassium chromate
solution as indicator. Adjust the normality exactly to 0.1.
3.1.5 Mrobenzene
3.1.6 Ferric Alum Indicator Solution
3.1.7 Ammonium Thiocyanate Solution -00’1 N.
*Specification for water, distilled quality
Prejaration-Weigh about 8’5 g of ammonium thiocyanate
and dissolve it in 1 litre of water in a volumetric flask. Shake well, and
standardize by titrating against 0’1 N silver nitrate solution using ferric
alum solution as indicator. Adjust the normality exactly to O-1.
Weigh accurately sufficient quantity of the admixture such that
about 0.1 g of chloride is present in the sample. Add enough hot water
SO as to make a volume of 150 ml, stir until dissolution is complete.
If there is insoluble matter, filter and wash with water. Make up the
clear solution thus obtained to a volume of 250 ml with water, shake
well.
Pipette 50 ml of the solution into a 250-ml conical flask containing
5 ml of 6 _N nitric acid. Add 10 to 15 ml of 0’1 N silver nitrate
solution from the burette. Then add 2 to 3 ml of nitrobenzene and 1 ml
ferric alum indicator and shake vigorously to coagulate the precipitate.
Titrate the excess silver nitrate with 0.1 N ammonium thiocyanate
until a permanent faint reddish brown colouration appears. Repeat the
titration with another 50 ml portion.
From the volume of silver nitrate ( AgNOs ) solution added subtract
the volume of thiocyanate solution required. Take the average of
the two determinations. Calculate the percentage .of chloride (Cl) in the
sample:1 ml 0.1 N AgNOs = 0.003 546 g, Ci
4.1 Reagents
4.1.1 Concentrated Nitric Acid
4.1.2 Dilute Nitric Acid - 1 : 50.
4.1.3 Silver Nitrate solution - approximately 0’1 N ( see 3.1.4 ).
4.1.4 Dilute Hydrochloric Acid - 1 : 100.
Procedure
Weigh out accurately sufficient quantity of the admixture such that
about 0.05 g of chloride is present in the sample. Add enough hot water
s’o as to make a volume of 150 ml, stir until the dissolution is complete.
Filter and wash with water if, there is insoluble matter. Add 1 to 2 ml
of concentrated nitric acid. Then add the silver nitrate solution slowly
and with constant stirring until the precipitation is complete. Add a
slight excess ( 5 to 10 ml ) of the silver nitrate solution. -Heat the suspension
nearly to boiling, while stirring constantly and maintain it at this temperature until the precip2tate coagulate3 and the supernatural
liquid is clear. Set aside the beaker in the dark .for one hour and filter
through a previously weighed sintered glass or porcelain crucible. Transfer
the last traces of silver chloride adhering to the beaker with a
policeman. Wash the precipitate in the crucible with 1 : 50 nitric acid
added in small portions until 3 to 5 ml of the washings collected in a test
tube give no turbidity with 1 or .2 drops of dilute hydrochloric acid. Dry
the crucible and contents in an air-oven at 130 to 150°C for one hour.
Allow to cool in a desiccator and weigh. Repeat the process of drying
and cooling until constant weight is attained.
calculate the percentage -of chloride in the sample:
0’1 g AgCl - 0.024737 Ci
Apparatus
Turbidimeter
Reagents
Dilute Ntric Acid - 1 : 3.
Silver Ntrate Solution
Standard Sodium Chloride Solution
Preparation - Weigh accurately 0’164 9 g of sodium chloride
( previously dried at 105 to 110°C for 2 h ) and dissolve in 1 000 ml of
distilled water in a volumetric flask. This solution contains 100 ppm
chloride, that is, 100 mg/l.
Procedure
Calibration of the Turbidimeter -Take 5 ml of dilute nitric acid
in a loo-ml volumetric flask, add 5 ml of silver nitrate solution and
make up the volume with distilled water. Shake well and use the solution
as ‘ blank ’ for adjusting the ‘ z&o ’ of the galvanometer. Take
20 ml of the standard sodium chloride solution in a loo-ml volumetric
flask, add 5 ml of dilute nitric acid and 50 to 60 ml distilled water. Shake
well and add 5 ml of silver nitrate solution and make up the volume with
distilled water. Shake well and use this turbid solution to adjust the
galvanometer deflection to full ~scale.
Run in 1’0, 2’5, 5.0, 7’5, 10’0, 15’0, 17’5 and 20.0 ml standard
chloride solution from a burette into separate lOO-ml volumetric flasks.
Take the first flask, add 5 ml of dilute nitric acid and 50 to 60 ml distilled
water. Shake well, add 5 ml of silver nitrate solution and make up the volume with ~distilled water. Shake well and measure the turbidity
after checking the galvanometer c zero ’ again.
Repeat the above procedure with the remaining solutions.
Plot the galvanometer readings against chloride concentration
in ppm.
Determination of Chloride in the Test Sample-Weigh accurately
sufficient quantity of admixture such that $it contains about 0’01 g of chloride
and boil with 100 to 150 ml distilled water. Filter and wash with hot
distilled water. Collect the filtrate and washings into a 500-ml volumetric
flask and make up the volume. Take 50 ml (see Note) of this solution
into a loo-ml ‘volumetric flask, add 5 ml dilute nitric acid and 5 ml
silver nitrate solution, and make up the volume with distilled water.
Shake well and measure the turbidity after checking the galvanometer
‘ zero ‘. Read the chloride ion concentration in ppm from the calibration
plot prepared earlier and then calculate the percentage of chloride
in the sample.
Percentage chloride = ---
Weight of chloride in g x loo
Weight of the sample taken
NOTE-Suitable dilutions may have to be carried out such that the galvanometer
reading falls within the range 2 to 15 ppm chloride whenever it is found necessary
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