Specification for Methods of Test for Determination of Water Soluble Chlorides in Concrete Admixtures
1973 Edition

Overview of the Standard Scope

• Defines procedures for measuring chloride levels in concrete admixtures.
• Chloride measurement is critical to prevent steel reinforcement corrosion.
• Involves preparing test solutions, reagent addition, and turbidity measurement to estimate chloride concentration.

Core Formula for Chloride Percentage:

[ \text{Chloride %} = \frac{\text{Mass of chloride (g)}}{\text{Mass of sample (g)}} \times 100 ]

Summary of Test Steps (Clause 5.3.2):

• Weigh admixture targeting ~0.01 g chloride.
• Boil with 100-150 ml distilled water; filter and rinse.
• Dilute filtrate to 500 ml.
• Take 50 ml aliquot, add 5 ml dilute nitric acid and 5 ml silver nitrate.
• Dilute to 100 ml, mix thoroughly.
• Measure turbidity and determine chloride concentration from calibration.
• Calculate chloride percentage using the formula.

Notes:

• Adjust dilution to keep readings within 2-15 ppm.
• Use distilled water conforming to IS:2-1960.
• Utilize 0.1 N ammonium thiocyanate in related steps.

flowchart TD
    A[Sample Weighing (~0.01 g Cl)] --> B[Boil with Distilled Water]
    B --> C[Filter and Wash]
    C --> D[Dilute to 500 ml]
    D --> E[Take 50 ml Aliquot]
    E --> F[Add 5 ml Dilute HNO3 + 5 ml AgNO3]
    F --> G[Dilute to 100 ml and Mix]
    G --> H[Measure Turbidity]
    H --> I[Read Chloride ppm from Calibration]
    I --> J[Calculate Chloride Percentage]

This section ensures precise chloride determination to evaluate admixture quality.

Guidelines for Method Selection (IS 6925)

• Available methods include volumetric, gravimetric, and turbidimetric techniques.
• Selection depends on chloride concentration:
  • For chloride content ≥ 1%, use volumetric titration.
  • For concentrations below 1%, gravimetric or turbidimetric methods are suitable.
  • Turbidimetric is preferred for very low chloride levels.
• Volumetric method is faster and less cumbersome compared to gravimetric.

Method Selection Table:

Method Summaries:

• Volumetric involves titration with silver nitrate.
• Gravimetric precipitates silver chloride for weighing.
• Turbidimetric measures turbidity caused by silver chloride formation.

flowchart TD
    A[Chloride Level] --> B{≥ 1%?}
    B -- Yes --> C[Volumetric Method]
    B -- No --> D{Very Low?}
    D -- Yes --> E[Turbidimetric Method]
    D -- No --> F[Gravimetric Method]

This structure guarantees accurate chloride analysis per IS 6925.

Reagents and Their Preparation According to IS 6925

• Purity Requirements (Clause 3.1.0): Use chemicals free from contaminants and distilled water per IS:1070-1960.

• Ammonium Thiocyanate Solution (0.1 N) (Clause 3.1.7): Prepare by dissolving the appropriate equivalent weight in distilled water to achieve 0.1 normality.

• Silver Nitrate Solution (Clause 5.2.2): Prepare as specified, typically standardized for titrations.

• Standard Sodium Chloride Solution (Clause 5.2.3): Dissolve a known quantity of sodium chloride in distilled water to create a reference solution.

Normality Calculation:

[ N = \frac{\text{grams of solute} \times \text{valence}}{\text{equivalent weight} \times \text{volume (liters)}} ]

Reagent Preparation Summary:

flowchart LR
    A[High Purity Chemicals & Distilled Water] --> B[Prepare Ammonium Thiocyanate]
    B --> C[Prepare Silver Nitrate Solution]
    B --> D[Prepare Sodium Chloride Solution]

Following these specifications ensures consistent reagent quality and test accuracy.

Volumetric Technique for Chloride Estimation (IS 6925)

Applicability

• Recommended for chloride levels ≥ 1%.
• Favoured for being faster and less labor intensive than gravimetric.
• Turbidimetric is reserved for very low concentrations.

Procedure Highlights

• Titrate chloride ions with a standardized silver nitrate solution.
• Use potassium chromate as an indicator; endpoint detected by red silver chromate formation.

Calculation Formula:

[ \text{Chloride %} = \frac{V \times N \times 35.45}{W} \times 100 ]

Where:

• (V) = volume of silver nitrate used (ml)
• (N) = normality of silver nitrate
• 35.45 = atomic mass of chloride
• (W) = sample weight (g)

Typical Normality Selection Table:

flowchart TD
    A[Prepare Sample] --> B[Add Potassium Chromate Indicator]
    B --> C[Titrate with Silver Nitrate]
    C --> D{Color Change Observed?}
    D -- No --> C
    D -- Yes --> E[Record Volume Used]
    E --> F[Calculate Chloride Percentage]

This method provides a rapid and straightforward approach for chloride concentrations above 1%.

Gravimetric Procedure for Chloride Quantification (IS 6925)

Key Steps (Clause 4.2.1)

• Prepare a sample containing approximately 0.05 g chloride.
• Dissolve in about 150 ml hot water, then add 1-2 ml concentrated nitric acid.
• Slowly add silver nitrate solution with stirring, including a 5-10 ml excess.
• Heat near boiling until precipitate coagulates and supernatant clears.
• Allow to stand in darkness for one hour.
• Filter through a pre-weighed sintered glass or porcelain crucible.
• Wash precipitate with 1:50 nitric acid until washings show no turbidity with dilute hydrochloric acid.
• Dry at 130-150°C for 1 hour, cool in a desiccator, weigh.
• Repeat drying and weighing until constant mass is achieved.

Calculation:

[ \text{Chloride %} = \frac{\text{Mass of AgCl} \times 35.453}{143.32 \times \text{Mass of sample}} \times 100 ]

(Molar masses: AgCl = 143.32 g/mol, Cl = 35.453 g/mol)

Notes:

• Typically used when chloride content exceeds 2.5%.
• More precise but more time-consuming than volumetric.
• Ensures thorough precipitation and washing to avoid impurities.

flowchart TD
    A[Weigh Sample (~0.05 g Cl)] --> B[Dissolve in Hot Water + Nitric Acid]
    B --> C[Add Silver Nitrate Slowly + Excess]
    C --> D[Heat till Precipitate Coagulates]
    D --> E[Stand in Dark for 1 Hour]
    E --> F[Filter Precipitate]
    F --> G[Wash with Dilute Nitric Acid]
    G --> H[Dry and Weigh]
    H --> I[Repeat Drying till Constant Weight]
    I --> J[Calculate Chloride Percentage]

This gravimetric method offers accurate chloride measurement through precipitate mass.

Turbidimetric Analysis of Chloride (IS 6925)

Calibration and Measurement

• Prepare a blank solution with 5 ml dilute nitric acid and 5 ml silver nitrate in a 100 ml volumetric flask; set galvanometer zero.
• Prepare full-scale calibration solution with 20 ml standard sodium chloride, 5 ml dilute nitric acid, 50-60 ml distilled water, and 5 ml silver nitrate; set galvanometer full scale deflection.
• Generate calibration curve using standard chloride volumes (1.0 to 20.0 ml) treated similarly.
• Measure turbidity (galvanometer deflection) of each standard after zeroing.

Important Calculation:

[ 0.1 \text{ g AgCl} = 0.024737 \text{ g chloride} ]

Calibration Data Example:

This calibration enables determination of chloride in unknown samples by comparing turbidity readings.

flowchart LR
    A[Prepare Blank Solution] --> B[Set Galvanometer Zero]
    C[Prepare Full Scale Solution] --> D[Set Galvanometer Full Scale]
    E[Prepare Standard Solutions with Varying NaCl Volumes] --> F[Measure Turbidity]
    F --> G[Plot Calibration Curve]
    G --> H[Determine Chloride in Samples]

Sample Preparation Procedure (IS 6925)

Steps (Clause 3.2.1):

• Weigh admixture to contain approximately 0.1 g chloride.
• Add hot water to make 150 ml, stirring until fully dissolved.
• Filter to remove insoluble matter; wash residue.
• Dilute the clear filtrate to 250 ml and mix well.

Chloride Precipitation (Clause 4.2.1):

• Take sample with ~0.05 g chloride.
• Dissolve in 150 ml hot water.
• Filter if insolubles are present.
• Add 1-2 ml concentrated nitric acid.
• Add silver nitrate gradually while stirring until precipitation finishes.
• Add excess silver nitrate (5-10 ml).
• Heat near boiling until precipitate coagulates and supernatant clears.
• Leave in dark for 1 hour.
• Filter through pre-weighed sintered glass or porcelain crucible.
• Wash precipitate with 1:50 nitric acid until washings become clear.
• Dry at 130-150°C for 1 hour, cool in desiccator, weigh.
• Repeat drying and weighing till constant weight achieved.

Standard Sodium Chloride Solution (Clause 5.2.3.1):

• Dissolve 0.1649 g dried sodium chloride in 1000 ml distilled water.
• This yields a 100 ppm chloride solution.

Reporting Guidelines:

• Round results as per IS 2-1960.

Summary Table:

flowchart TD
    A[Weigh Sample (~0.05-0.1 g Cl)] --> B[Dissolve in Hot Water (150 ml)]
    B --> C[Filter if Insoluble Matter]
    C --> D[Add Nitric Acid (1-2 ml)]
    D --> E[Add Silver Nitrate Slowly + Excess]
    E --> F[Heat and Coagulate Precipitate]
    F --> G[Stand in Dark for 1 Hour]
    G --> H[Filter Precipitate]
    H --> I[Wash with Dilute Nitric Acid]
    I --> J[Dry and Weigh Until Constant Weight]

This ensures proper sample preparation for accurate chloride testing.

Calculation of Chloride Content as per IS 6925

Volumetric Method (Clauses 2.1 & 3.2.1):

• Suitable for chloride levels ≥ 1%.
• Weigh sample to contain ~0.1 g chloride.
• Dissolve in hot water, make volume to 150 ml.
• Filter if necessary.
• Dilute to 250 ml.
• Titrate with silver nitrate to find chloride concentration.

Gravimetric Method (Clause 2.2):

• Suitable for chloride above 2.5%.
• Precipitate chloride as silver chloride, filter, dry, and weigh.

Volumetric Calculation Formula:

[ \text{Chloride %} = \frac{V \times N \times 35.45 \times 100}{W} ]

Where:

• (V) = volume of silver nitrate titrant (ml)
• (N) = normality of silver nitrate
• 35.45 = atomic weight of chloride
• (W) = sample weight (g)

Summary Table:

flowchart TD
    A[Weigh Sample] --> B[Dissolve in Hot Water]
    B --> C[Filter if Required]
    C --> D[Dilute to 250 ml]
    D --> E[Titrate with Silver Nitrate]
    E --> F[Calculate Chloride Percentage]

This ensures precise quantification of chloride content in admixtures.

Reporting Protocols for Chloride Determination (IS 6925)

1. Rounding Off:

   • Follow IS 2-1960 for rounding numerical results.

2. Chemical Quality:

   • Use only pure reagents and distilled water per IS 1070-1960.

3. Chloride Determination (Clause 5.3.2):

   • Weigh admixture with ~0.01 g chloride.
   • Boil with 100-150 ml distilled water, filter and wash.
   • Dilute filtrate to 500 ml.
   • Take 50 ml aliquot, add 5 ml dilute nitric acid and 5 ml silver nitrate.
   • Dilute to 100 ml, mix well.
   • Measure turbidity using galvanometer.
   • Record chloride concentration from calibration graph.
   • Calculate chloride percentage:

   [ \text{Chloride %} = \frac{\text{Mass of chloride (g)}}{\text{Mass of sample (g)}} \times 100 ]

   • Adjust dilution to keep galvanometer reading between 2 and 15 ppm.

Procedure Summary Table:

flowchart TD
    A[Weigh Sample (~0.01 g Cl)] --> B[Boil with Distilled Water]
    B --> C[Filter and Wash]
    C --> D[Make up to 500 ml]
    D --> E[Take 50 ml Aliquot]
    E --> F[Add Dilute HNO3 and AgNO3]
    F --> G[Dilute to 100 ml and Mix]
    G --> H[Measure Turbidity]
    H --> I[Determine Chloride Concentration]

These guidelines ensure consistent and accurate reporting.

Accuracy and Precision Considerations (IS 6925)

• Emphasis on calibration and measurement techniques affecting test reliability.

Calibration Process (Clauses 5.3.1 & 5.3.1.1):

• Prepare blank solution of dilute nitric acid and silver nitrate to zero galvanometer.
• Prepare full-scale calibration with standard sodium chloride and reagents.
• Generate a calibration curve by measuring turbidity of standard chloride solutions at various concentrations.

Maintaining Accuracy and Precision:

• Use high-purity chemicals and distilled water to minimize contamination.
• Repeat measurements to ensure reproducibility.
• Apply IS 2-1960 rounding rules for uniform reporting.

Calibration Concentrations:

flowchart LR
    A[Prepare Blank] --> B[Set Galvanometer Zero]
    C[Prepare Calibration Standards] --> D[Set Full Scale Deflection]
    D --> E[Measure Turbidity]
    E --> F[Plot Calibration Curve]
    F --> G[Use Curve for Sample Testing]

No explicit formulas for precision are provided but adherence to calibration and reagent purity ensures dependable results.

Safety Measures in Chloride Testing (IS 6925 Context)

Though IS 6925 does not explicitly detail safety protocols, general laboratory practices apply:

• Always wear appropriate personal protective equipment (PPE): gloves, goggles, lab coat.
• Handle corrosive chemicals such as silver nitrate and nitric acid with care to avoid skin contact.
• Ensure adequate ventilation when working with volatile reagents.
• Dispose of chemical wastes in accordance with local environmental regulations.
• Confirm galvanometer calibration and maintain readings within specified ranges (2-15 ppm chloride).

Chloride Percentage Formula (Clause 5.3.2):

[ \text{Chloride %} = \frac{\text{Mass of chloride (g)}}{\text{Mass of sample (g)}} \times 100 ]

Rounding Guidance:

• Apply IS 2-1960 for numerical rounding.

Chloride Determination Process Summary:

For detailed safety rules, refer to IS 4031 and IS 4032 covering physical and chemical laboratory protocols.

Key Formulas and References in IS 6925

Chloride Percentage Computation (Clause 5.3.2):

• Weigh admixture with ~0.01 g chloride.
• Boil with 100-150 ml distilled water, filter, dilute to 500 ml.
• Take 50 ml aliquot, add 5 ml dilute nitric acid and 5 ml silver nitrate.
• Dilute to 100 ml, measure turbidity.
• Calculate chloride percentage:

[ \text{Chloride %} = \frac{\text{Mass of chloride (g)}}{\text{Mass of sample (g)}} \times 100 ]

Note: Dilute samples to maintain galvanometer readings between 2 and 15 ppm.

Cross References to IS Standards:

• IS 2-1960: Guidelines for rounding off numbers.
• IS 269-1967, 455-1967, 650-1966, 1489-1967: Cement types.
• IS 4031-1968, 4032-1968: Physical and chemical cement tests.
• IS 4845-1968: Cement terminology.

Chloride Testing Procedure Summary:

This synopsis aligns with IS 6925:1973 requirements for chloride testing in concrete admixtures.