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

IS 6925: Scope - Key Points & Formula

Scope Summary:

• IS 6925 covers the determination of chloride content in admixtures.
• Chloride content is critical as it affects corrosion in reinforced concrete.
• Test involves preparing a sample solution, adding reagents, and measuring turbidity to find chloride concentration.

Key Formula for % Chloride:

[ \text{Percentage chloride} = \frac{\text{Weight of chloride in g}}{\text{Weight of sample taken}} \times 100 ]

Test Procedure Highlights (Clause 5.3.2):

• Weigh admixture containing ~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 + 5 ml silver nitrate.
• Make volume to 100 ml; shake well.
• Measure turbidity and read chloride ppm from calibration plot.
• Calculate chloride % using the formula above.

Important Notes:

• Dilutions may be necessary to keep galvanometer reading within 2-15 ppm.
• Use distilled water as per IS:2-1960 for rounding off values.
• Ammonium thiocyanate solution (0.1 N) is used in related procedures.

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

This scope ensures accurate chloride quantification to assess admixture quality per IS 6925.

IS 6925: Selection of Method for Chloride Determination

Key Points from Clauses:

• Methods Available (Clause 1.1):

  • Volumetric
  • Gravimetric
  • Turbidimetric

• Selection Criteria (Clause 2.0 & 2.1):

  • Use volumetric method if chloride concentration ≥ 1%.
  • Use gravimetric method or turbidimetric method for lower concentrations.
  • Turbidimetric method is preferred when chloride concentration is very low.
  • Volumetric method is quicker and less laborious than gravimetric (Clause 2.4).

Summary Table for Method Selection:

Additional Notes:

• The volumetric method typically involves titration with silver nitrate.
• Gravimetric involves precipitation and weighing of silver chloride.
• Turbidimetric measures turbidity caused by silver chloride precipitate.

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

This approach ensures accurate and efficient chloride determination as per IS 6925.

IS 6925: Key Formulas and Specifications for Reagents and Solutions

• Quality of Reagents (3.1.0):
  Use pure chemicals (free from impurities affecting analysis) and distilled water (per IS:1070-1960) for all tests.

• Ammonium Thiocyanate Solution (3.1.7):
  Prepare a 0.1 N solution for titrations.

  • Normality (N) relates to equivalents per liter.
  • For 0.1 N, dissolve the equivalent weight accordingly in distilled water.

• Silver Nitrate Solution (5.2.2):
  Refer to clause 4.1.3 for preparation details (typically standardized for titrations).

• Standard Sodium Chloride Solution (5.2.3):
  Used as a reference; prepare by dissolving a known mass of NaCl in distilled water to a fixed volume.

Typical Preparation Formula: Normality (N)

[ N = \frac{\text{grams of solute} \times \text{valency}}{\text{equivalent weight} \times \text{volume in liters}} ]

Summary Table for Common Solutions

flowchart LR
    A[Pure Chemicals & Distilled Water] --> B[Prepare Reagents]
    B --> C[Ammonium Thiocyanate 0.1 N]
    B --> D[Silver Nitrate Solution]
    B --> E[Sodium Chloride Solution]

Use these specifications to ensure reagent quality and accurate test results per IS 6925.

IS 6925: Volumetric Method for Chloride Determination

Applicability

• Used when chloride concentration ≥ 1% (Clause 2.1).
• Preferred over gravimetric if choice is open, as it is quicker and less laborious (Clause 2.4).
• Turbidimetric method is for very low chloride concentrations.

Key Points

• Volumetric titration involves reacting chloride ions with a standard silver nitrate (AgNO3) solution.
• Endpoint detected by color change using potassium chromate indicator (formation of red silver chromate precipitate).

Basic Formula

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

Where:

• (V) = volume of AgNO3 used (ml)
• (N) = normality of AgNO3
• (35.45) = molecular weight of chloride ion
• (W) = weight of sample (g)

Typical Table: Normality vs. Chloride Range

flowchart TD
    A[Sample Preparation] --> B[Add Potassium Chromate Indicator]
    B --> C[Titrate with AgNO3]
    C --> D{Color Change?}
    D -- No --> C
    D -- Yes --> E[Record Volume of AgNO3]
    E --> F[Calculate Chloride % using formula]

Summary: Use volumetric method for chloride ≥1%, titrate with AgNO3, calculate chloride % using volume and normality. Preferred for speed and ease.

Gravimetric Method for Chloride Determination (IS 6925)

Key Specifications (Clause 4.2.1)

• Sample quantity: Enough to contain ~0.05 g Cl⁻.
• Dissolve in 150 ml hot water, add 1-2 ml conc. HNO₃.
• Add AgNO₃ solution slowly with stirring; add slight excess (5-10 ml).
• Heat near boiling until precipitate coagulates and supernatant clears.
• Set aside in dark for 1 hour.
• Filter through pre-weighed sintered glass/porcelain crucible.
• Wash precipitate with 1:50 HNO₃ until washings show no turbidity with dilute HCl.
• Dry at 130-150°C for 1 hour, cool in desiccator, weigh.
• Repeat drying/cooling until constant weight.

Calculation

• Weight of AgCl precipitate gives chloride content.
• Chloride % = (\frac{\text{Weight of AgCl} \times 35.453}{143.32 \times \text{Weight of sample}}) × 100
  (Molar masses: AgCl = 143.32 g/mol, Cl = 35.453 g/mol)

Notes

• Preferred when chloride > 2.5%.
• More accurate but laborious than volumetric method.
• Ensure complete precipitation and thorough washing to avoid impurities.

flowchart TD
    A[Weigh Sample (~0.05g Cl)] --> B[Dissolve in 150 ml hot water + 1-2 ml HNO3]
    B --> C[Add AgNO3 slowly with stirring + slight excess]
    C --> D[Heat near boiling, stir until coagulation]
    D --> E[Set aside 1 hour in dark]
    E --> F[Filter through pre-weighed crucible]
    F --> G[Wash with 1:50 HNO3 until clear]
    G --> H[Dry at 130-150°C, cool, weigh]
    H --> I[Repeat drying until constant weight]
    I --> J[Calculate % Chloride from AgCl weight]

This method ensures precise chloride quantification via silver chloride precipitation and gravimetric measurement.

Turbidimetric Method (IS 6925)

Key Specifications & Procedure

• Calibration (Clause 5.3.1):

  • Prepare blank:
    • 5 ml dilute nitric acid + 5 ml silver nitrate in 100 ml flask, make up with distilled water.
    • Adjust galvanometer zero with this.
  • Prepare full scale:
    • 20 ml standard NaCl + 5 ml dilute nitric acid + 50–60 ml distilled water + 5 ml silver nitrate solution in 100 ml flask.
    • Adjust galvanometer full scale deflection.

• Standard Curve Preparation (Clause 5.3.1.1):

  • Use volumes of standard chloride solution: 1.0, 2.5, 5.0, 7.5, 10.0, 15.0, 17.5, 20.0 ml.
  • For each: add 5 ml dilute nitric acid + 50–60 ml distilled water + 5 ml silver nitrate, make up to 100 ml.
  • Measure turbidity (galvanometer deflection) after zero adjustment.

Important Calculation (Clause 4.2.2):

• Chloride content:
  [ 0.1,g,AgCl = 0.024737,g,Cl ]

Summary Table: Standard Chloride Volume vs Turbidity

This calibration curve allows determination of chloride concentration in unknown samples by comparing turbidity readings.

flowchart LR
A[Prepare Blank] --> B[Set Galvanometer Zero]
C[Prepare Full Scale Solution] --> D[Set Galvanometer Full Scale]
E[Prepare Standard Solutions (1-20 ml)] --> F[Measure Tur

IS 6925: Procedure for Sample Preparation - Key Points

Sample Preparation (Clause 3.2.1)

• Weigh admixture to contain ~0.1 g chloride.
• Add hot water to make 150 ml, stir until dissolved.
• Filter if insoluble matter present; wash residue.
• Make up clear solution to 250 ml with water, shake well.

Chloride Precipitation (Clause 4.2.1)

• Weigh admixture for ~0.05 g chloride.
• Add hot water to 150 ml, dissolve completely.
• Filter if insoluble matter present.
• Add 1-2 ml concentrated nitric acid.
• Add silver nitrate slowly with stirring until precipitation complete.
• Add excess silver nitrate (5-10 ml).
• Heat near boiling; maintain until precipitate coagulates and supernatant clears.
• Keep in dark for 1 hour.
• Filter through weighed sintered glass/porcelain crucible.
• Wash precipitate with 1:50 nitric acid until washings show no turbidity with dilute HCl.
• Dry at 130-150°C for 1 hour, cool in desiccator, weigh.
• Repeat drying/cooling till constant weight.

Standard Chloride Solution (Clause 5.2.3.1)

• Dissolve 0.1649 g NaCl (dried at 105-110°C for 2 hours) in 1000 ml distilled water.
• This yields 100 ppm chloride (100 mg/L) standard solution.

Reporting (Clause 0.3)

• Round off results as per IS 2-1960 guidelines.

Summary Table for Sample Preparation

flowchart TD
    A[Weigh admixture (~0.05-0.1 g

IS 6925: Calculation of Chloride Content in Concrete Admixtures

Key Methods:

• Volumetric Method (Clause 2.1 & 3.2.1)

  • Suitable for chloride concentration ≥ 1%.
  • Procedure:
    • Weigh admixture to contain ~0.1 g chloride.
    • Dissolve in hot water, make volume to 150 ml.
    • Filter if insoluble matter present.
    • Dilute filtrate to 250 ml.
    • Perform titration (usually with silver nitrate) to find chloride content.

• Gravimetric Method (Clause 2.2)

  • Suitable for chloride concentration > 2.5%.
  • Chloride is precipitated (e.g., as AgCl), filtered, dried, and weighed.

Typical Calculation (Volumetric Method):

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

Where:

• ( V ) = Volume of titrant (AgNO₃) used (ml)
• ( N ) = Normality of AgNO₃
• 35.45 = Atomic weight of chlorine
• ( W ) = Weight of sample (g)

Summary Table:

flowchart TD
    A[Weigh Sample] --> B[Dissolve in Hot Water]
    B --> C[Filter if Insoluble]
    C --> D[Dilute to 250 ml]
    D --> E[Titrate with AgNO3]
    E --> F[Calculate Chloride %]

This ensures chloride content in admixtures is accurately determined per IS 6925.

IS 6925: Reporting of Results - Key Points

1. Rounding Off Results

   • Follow IS 2-1960 for rounding off final observed or calculated values.

2. Quality of Reagents

   • Use pure chemicals and distilled water as per IS 1070-1960.
   • Pure chemicals must be free from impurities affecting analysis.

3. Determination of Chloride Content (Clause 5.3.2)

   • Weigh admixture containing ~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 + 5 ml silver nitrate, dilute to 100 ml.
   • Measure turbidity; read chloride ppm from calibration plot.
   • Calculate % chloride:

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

   • Adjust dilution so galvanometer reading is between 2 to 15 ppm chloride.

Summary Table: Chloride Determination Procedure

flowchart TD
    A[Weigh sample (~0.01 g Cl)] --> B[Boil with 100-150 ml distilled water]
    B --> C[Filter and wash]
    C --> D[Make up volume to 500 ml]
    D --> E[Take 50 ml aliquot]
    E --> F[Add 5 ml dilute H

IS 6925: Accuracy and Precision - Key Points

The code primarily addresses calibration and measurement procedures for turbidity, which impact accuracy and precision indirectly:

Calibration Procedure (Clause 5.3.1 & 5.3.1.1)

• Use standard solutions with known chloride concentrations (1.0 to 20.0 ml of standard chloride solution diluted to 100 ml).
• Prepare a blank solution with dilute nitric acid and silver nitrate to set galvanometer zero.
• Adjust galvanometer deflection to full scale using turbid standard solution.
• Measure turbidity of each standard solution to create a calibration curve.

Accuracy & Precision Control

• Use pure chemicals and distilled water (Clause 3.1.0) to avoid impurities affecting results.
• Repeat measurements for multiple standard concentrations to ensure repeatability and linearity.
• Round off results per IS 2-1960 for consistent reporting.

Summary Table: Calibration Concentrations for Turbidimeter

flowchart LR
    A[Prepare Blank Solution] --> B[Set Galvanometer Zero]
    C[Prepare Standard Solutions] --> D[Adjust Galvanometer Full Scale]
    D --> E[Measure Turbidity of Each Solution]
    E --> F[Plot Calibration Curve]
    F --> G[Use Curve for Sample Measurement]

Note: IS 6925 does not provide explicit formulas for accuracy/precision; these are ensured by strict calibration and reagent purity.

IS 6925: Safety Precautions - Key Points

The provided context from IS 6925 (1973) mainly covers chemical testing procedures and references to related IS codes, with no explicit clause on safety precautions. However, standard safety practices in handling chemicals and testing admixtures apply:

General Safety Precautions for Chemical Testing (IS 6925 context):

• Use Personal Protective Equipment (PPE): Gloves, goggles, lab coat.
• Handle Chemicals Carefully: Silver nitrate and nitric acid are corrosive; avoid skin contact.
• Work in Ventilated Areas: To avoid inhalation of fumes.
• Proper Disposal: Follow local regulations for chemical waste.
• Calibration and Measurement: Ensure instruments (e.g., galvanometer) are zeroed and readings are within specified ranges (2-15 ppm chloride).

Key Formula from Clause 5.3.2 for Chloride Percentage:

[ \text{Percentage Chloride} = \frac{\text{Weight of chloride in g}}{\text{Weight of sample taken}} \times 100 ]

References for Rounding Off:

• Follow IS 2:1960 for rounding off test values.

Summary Table: Chloride Determination Procedure (Clause 5.3.2)

If you need detailed safety clauses, refer to IS 4031 (Physical tests for hydraulic cement) or IS 4032 (Chemical analysis of hydraulic cement) for laboratory safety norms.

flowchart TD
    A[Sample Weighing] --> B[Boil with Distilled Water]
    B --> C[Filter & Wash]
    C --> D[Make up to 500 ml]
    D --> E[Take 50 ml

IS 6925 - Key Formulas & Specifications for Chloride Determination

Chloride Percentage Calculation (Clause 5.3.2)

• Weigh admixture containing ~0.01 g chloride.
• Boil with 100-150 ml distilled water, filter, and dilute to 500 ml.
• Take 50 ml aliquot, add 5 ml dilute nitric acid + 5 ml silver nitrate, dilute to 100 ml.
• Measure turbidity; read chloride ppm from calibration plot.
• Calculate % chloride as:

[ \text{Percentage chloride} = \frac{\text{Weight of chloride in g}}{\text{Weight of sample taken}} \times 100 ]

Note: Dilute sample to keep galvanometer reading between 2-15 ppm chloride.

References to Other IS Codes

• IS 2-1960: Rounding off rules.
• IS 269-1967, 455-1967, 650-1966, 1489-1967: Types of cement.
• IS 4031-1968, 4032-1968: Physical and chemical tests for cement.
• IS 4845-1968: Cement terminology.

Summary Table: Chloride Test Procedure

This concise summary aligns with IS 6925:1973 requirements for chloride content testing in admixtures.