Methods of Test for Autoclaved Cellular Concrete Products, Part II: Determination of Drying Shrinkage
1972 Edition

IS 6441 Part 2 - Scope and Essential Details

Scope:

• Describes the standardized approach for measuring drying shrinkage in autoclaved cellular concrete products.
• Part of a multipart series covering different test methods for ACC (see table below).

Key Criteria & Formulas for Drying Shrinkage (Clauses 4.2.3 & 6.1)

• Shrinkage stabilization:
  Two sequential length measurements taken 7 days apart should not differ by more than 0.007% of the specimen's length.

• Report must include:

  • Standard code reference
  • Product identification
  • Manufacturing date
  • Sampling details (location, method, time)
  • Specimen dimensions and age at test commencement
  • Individual prism linear shrinkage and average values

Visual Overview of Shrinkage Testing

flowchart TD
    A[Prepare Test Specimens] --> B[Record Initial Length]
    B --> C[Subject Specimens to Drying]
    C --> D[Periodically Measure Length]
    D --> E{Are two measurements 7 days apart within 0.007%?}
    E -- No --> C
    E -- Yes --> F[Record Final Shrinkage Data]
    F --> G[Compile Report as per Clause 6.1]

This concise section defines the compliance requirements for drying shrinkage measurement under IS 6441 Part 2.

IS 6441 Part 2 (1972) - Essential References and Details

Part Series Summary (from Foreword)

Reporting Details (Clause 6.1)

Mandatory report contents:

• Reference to IS 6441 Part II
• Product identification
• Manufacture date
• Sampling location, procedure, and timing
• Specimen size and age at testing
• Linear shrinkage values (individual and mean)

Additional Points

• The standard is harmonized with international guidelines but customized for Indian environmental conditions.
• Contact information for BIS regional branches is provided for further assistance.

Fundamental Equation for Linear Shrinkage

[ \text{Linear Shrinkage (%) }= \frac{L_0 - L_t}{L_0} \times 100 ]

where:

• (L_0) = initial specimen length
• (L_t) = length at time (t)

flowchart TD
    A[Sample Preparation] --> B[Initial Length Measurement \(L_0\)]
    B --> C[Drying Period]
    C --> D[Length Measurement at Time \(t\) \(L_t\)]
    D --> E[Calculate Shrinkage]
    E --> F[Report Results Following Clause 6.1]

Refer to the full IS 6441 Part 2 document for detailed procedures and specimen specifications.

IS 6441 Part 2: Key Definitions and Specifications

• Scope: Focuses on measuring drying shrinkage in autoclaved cellular concrete products.

• Definition:

  • Drying Shrinkage refers to the contraction in length of ACC prisms due to moisture loss over time.

• Measurement Protocol (Clause 4.2.3):

  • Length readings are repeated until length stability is reached.
  • Stability is defined as two length measurements spaced 7 days apart differing by no more than 0.007% of the specimen length.

• Additional Notes:

  • The standard aligns with global practices, ensuring suitability for Indian field conditions (Clause 0.3).
  • The method monitors dimensional changes of prisms under controlled drying.

Summary Table: Length Measurement Stability Criteria

This guarantees consistent and accurate drying shrinkage determination for ACC materials.

IS 6441 Part 2: Equipment and Materials for Drying Shrinkage Testing

Instrument Specifications (Clause 3.1)

• Measurement Accuracy: ±0.003% of specimen length.
• Range: Must accommodate minor variations in gauge length.
• Contact: Ensure positive and stable contact with gauge plugs.
• Calibration: Instruments should be periodically checked against a standard reference.

Measurement Conditions (Clauses 4.2.2 & 4.2.3)

• Temperature: Maintain at 27 ± 2°C during measurements.
• Specimen Orientation: Consistent placement; take two measurements at 0° and after rotating specimen 90° about its longitudinal axis.
• Result Processing: Use average if two readings differ.
• Length Stability: Considered achieved when two readings 7 days apart differ by ≤ 0.007%.

Summary Table: Equipment Accuracy and Test Conditions

flowchart LR
    A[Prepare Specimen] --> B[Initial Length Measurement]
    B --> C{Rotate specimen 90°?}
    C -- Yes --> D[Second Measurement]
    D --> E[Average Length]
    E --> F[Repeat Weekly Measurements]
    F --> G{Length change ≤ 0.007%?}
    G -- No --> F
    G -- Yes --> H[Length Stability Confirmed]

These requirements ensure precise and repeatable drying shrinkage measurements per IS 6441 Part 2.

IS 6441 Part 2: Guidelines for Preparing Specimens for Drying Shrinkage Tests

Essential Requirements (Clause 2.3)

• Cutting: Use rotating carbo-rundum blades or equivalent tools to produce clean, flat cuts.
• Surface Flatness: Maximum diagonal deviation on the largest surface should not exceed 0.1 mm.
• Orientation of Specimens:
  • For samples shorter than 24 cm: length axis should be perpendicular to the rise direction.
  • For samples 24 cm or longer: length axis should be parallel to the rise direction.

Water Saturation Procedure (Clause 4.1)

• Immerse specimens with gauge plugs in water until their weight remains constant.
• Minimum soaking duration is 72 hours.
• Specimens with bulk density below 1 g/cm³ initially float; after 2 hours, they should be weighted down for full immersion.

Measurement Accuracy (Clause 3.1)

• Length measurements require an accuracy of ±0.003% of specimen length.
• Instruments must have adequate range and ensure positive contact with gauge plugs.
• Regular calibration is mandatory.

Summary Table: Orientation Based on Sample Height

flowchart TD
    A[Raw Sample] --> B[Cut Specimens Using Carbo-Rundum Blade]
    B --> C{Is Sample Height < 24 cm?}
    C -- Yes --> D[Set Length Axis ⟂ to Rise Direction]
    C -- No --> E[Set Length Axis ∥ to Rise Direction]
    D & E --> F[Verify Surface Flatness ≤ 0.1 mm]
    F --> G[Attach Gauge Plugs]
    G --> H[Soak Specimens in Water ≥ 72 hours]
    H --> I[Ready for Length Measurement]

This procedure standardizes specimen preparation for reliable drying shrinkage testing.

IS 6441 Part 2: Procedure for Conducting Drying Shrinkage Tests

Core Requirements

• Measurement Temperature:
  Conduct length measurements at 27 ± 2°C to maintain consistency (Clause 4.2.2).

• Specimen Positioning and Reading:
  Place specimens uniformly within the measuring apparatus. Take two readings:

  • First measurement
  • Second measurement after rotating the specimen by 90° along its longitudinal axis Use the average value if readings differ.

• Instrument Specifications (Clause 3.1):

  • Accuracy of 0.003% of specimen length
  • Sufficient measurement range for small variations
  • Positive contact with gauge plugs to ensure reproducibility
  • Regular calibration against a certified reference

• Rounding of Results:
  Final figures should be rounded according to IS 2-1960.

Summary Table: Measurement Parameters

flowchart LR
    A[Place Specimen in Device] --> B[Take First Measurement]
    B --> C[Rotate Specimen 90°]
    C --> D[Take Second Measurement]
    D --> E{Readings Identical?}
    E -- Yes --> F[Use Reading]
    E -- No --> G[Calculate Average]
    F & G --> H[Round and Record per IS 2-1960]

This sequence ensures accurate and reproducible drying shrinkage results.

IS 6441 Part 2: Key Aspects of Drying Shrinkage Measurement

• Specimen Size and Shape (Clause 2.1):

  • Square prism cross-section of 40 mm × 40 mm
  • Minimum length of 150 mm to fit measurement equipment

• Specimen Type:

  • Unreinforced prisms

• Measurement Method:

  • Measure length changes over drying time.
  • Calculate drying shrinkage strain (\varepsilon_{sh}) as:

[ \varepsilon_{sh} = \frac{\Delta L}{L_0} \times 10^6 \quad \text{(microstrain, } \mu\varepsilon\text{)} ]

where:

• (\Delta L = L_0 - L_t)

• (L_0) = initial length

• (L_t) = length at time (t)

• Testing Environment:

  • Specimens are conditioned in controlled drying surroundings (typically 50% relative humidity at 23°C) after curing.

Summary Table: Specimen Dimensions

flowchart TD
    A[Fabricate Concrete Prism] --> B[Initial Curing]
    B --> C[Measure Initial Length (L0)]
    C --> D[Drying Under Controlled Conditions]
    D --> E[Measure Length at Time t (Lt)]
    E --> F[Compute Shrinkage Strain \(\varepsilon_{sh}\)]

This approach guarantees uniform and comparable drying shrinkage data for autoclaved cellular concrete.

IS 6441 Part 2: Environmental Conditions for Testing

• Storage and Humidity Chamber (Clause 3.4):

  • Temperature maintained at 27 ± 2°C
  • Relative humidity stabilized using saturated potassium carbonate (K₂CO₃) solution
  • Purpose is to subject specimens to controlled drying conditions.

• Measurement Environment (Clause 4.2.2):

  • Maintain temperature at 27 ± 2°C during length measurements
  • Specimens measured twice: initially and after 90° rotation about the longitudinal axis
  • Use average if readings differ

Potassium Carbonate Solution Humidity Reference

• Saturated K₂CO₃ solution provides approximately 43% relative humidity at 27°C (equilibrium state).

Summary Table:

flowchart LR
    A[Specimen Storage] --> B[Humidity Chamber with K2CO3 Solution]
    B -->|Maintain 27 ± 2°C| C[Specimen Conditioning]
    C --> D[Measurement Unit]
    D --> E[Reading 1 (0°)]
    D --> F[Reading 2 (90° rotation)]
    E & F --> G[Average Readings if Different]

This ensures stable environmental conditions for accurate and repeatable testing.

IS 6441 Part 2: Computation and Reporting of Shrinkage Data

Key Clauses

• Length Stability (Clause 4.2.3):
  Length measurements continue until two consecutive values, spaced 7 days apart, differ by no more than 0.007% of specimen length.

• Measurement Accuracy (Clause 3.1):

  • Accuracy: ±0.003% of specimen length
  • Instruments must cover small gauge length variations
  • Positive contact with gauge plugs required
  • Regular calibration against standard references

• Rounding:
  Values should be rounded as per IS 2-1960.

Formula for Length Change (%)

[ \text{Length Change (5)} = \frac{L_t - L_0}{L_0} \times 100 ]

where:

• (L_0) = initial length
• (L_t) = length at time (t)

Summary Table: Measurement Criteria

flowchart TD
    A[Begin Measurement] --> B[Record Initial Length L0]
    B --> C[Wait 7 Days]
    C --> D[Record Length Lt]
    D --> E{Is difference ≤ 0.007% of L0?}
    E -- No --> C
    E -- Yes --> F[Length Stability Achieved]
    F --> G[Calculate Percentage Length Change]
    G --> H[Report Rounded Results]

This method ensures standardized, reliable length measurement and reporting.

IS 6441 Part 2 - Test Reporting Requirements (Clause 6.1)

The report on linear shrinkage testing must specify:

• a) Code reference: Identification of the applicable IS standard.
• b) Product details: Type and brand of cement.
• c) Manufacture date: Date when the cement was produced.
• d) Sampling information: Location, method, and timing of sample collection.
• e) Specimen details: Size and age at the start of testing.
• f) Linear shrinkage data: Values for individual prisms and the average shrinkage.

Additional Information:

• Length measurements are continued until length stabilization is confirmed (two measurements 7 days apart within 0.007% difference).
• Final results should be rounded according to IS 2-1960.
• Linear shrinkage is calculated as:

[ \text{Shrinkage (%) }= \frac{L_0 - L_t}{L_0} \times 100 ]

where:

• (L_0) is the initial length
• (L_t) is the length at time (t)

Summary Table: Reporting Elements

flowchart TD
    A[Test Initiation] --> B[Document Specimen Size & Age]
    B --> C[Measure Initial Length L0]
    C --> D[Periodic Length Measurements Lt]
    D --> E{Are two measurements 7 days apart within 0.007%?}
    E -- No --> D
    E -- Yes --> F[Calculate Shrinkage Percentage]
    F --> G[Generate Report Following Clause 6.1]
    G --> H[Test Completion]

This ensures thorough and standardized documentation in accordance with IS 6441 Part 2.

IS 6441 Part 2: Key Points on Measurement Accuracy and Precision

1. Measurement Accuracy (Clause 3.1a)

• Required accuracy is 0.003% of specimen length.
• For example, a 100 mm specimen must have a maximum error of ±0.003 mm.

2. Repeatability of Measurements (Clause 4.2.3)

• Two consecutive measurements taken 7 days apart must be within 0.007% of specimen length.
• This confirms length stabilization prior to final reporting.

3. Measurement Process (Clause 4.2.2)

• Temperature controlled at 27 ± 2°C.
• Specimen consistently positioned.
• Two readings taken with specimen rotated 90° around its axis.
• Average used if readings differ.

4. Instrument Specifications (Clause 3.1)

• Sufficient measurement range to cover gauge length variations.
• Positive contact with gauge plugs to ensure reproducibility.
• Regular calibration against a traceable standard.

5. Result Reporting (Clause 0.5)

• Round values according to IS 2-1960.

Summary Table: Accuracy and Repeatability

flowchart TD
    A[Start Measurement] --> B[Set Temperature 27 ± 2°C]
    B --> C[Place Specimen Uniformly]
    C --> D[Take First Reading]
    D --> E[Rotate Specimen 90°]
    E --> F[Take Second Reading]
    F --> G{Difference ≤ 0.003%?}
    G -- Yes --> H[Average Readings]
    G -- No --> I[Repeat Measurement]
    H --> J[Repeat After 7 Days]
    J --> K{Difference ≤ 0.007%?}
    K -- Yes --> L[Accept Measurement]
    K -- No --> I

This guarantees high precision and reproducibility as per the standard.

IS 6441 Part 2 (1972) — Summary of Notes and Recommendations

This section covers the determination of drying shrinkage for autoclaved cellular concrete products.

Reporting Requirements (Clause 6.1)

• Reports must include:
  • Standard code reference
  • Product identification
  • Manufacture date
  • Sampling details (location, method, time)
  • Specimen size and test age
  • Individual and average linear shrinkage values

Measurement Stability (Clause 4.2.3)

• Length measurements continue until a constant length is confirmed.
• Constant length is defined as two consecutive readings 7 days apart differing by no more than 0.007% of specimen length.

Shrinkage Calculation (Clause 5)

• Linear shrinkage (%) is calculated as:

[ \frac{L_0 - L_t}{L_0} \times 100 ]

where:

• (L_0) is the initial length
• (L_t) is the length after drying

Overview of IS 6441 Series

This standard aligns with international norms and is customized for Indian climatic and field conditions.

flowchart TD
    A[Start Drying Shrinkage Test] --> B[Record Initial Length (L0)]
    B --> C[Dry Specimen Under Controlled Conditions]
    C --> D[Periodic Length Measurements (Lt)]
    D --> E{Is difference between consecutive measurements ≤ 0.007%?}
    E -- No --> C
    E -- Yes --> F[Calculate Shrinkage Percentage]
    F --> G[Prepare and Submit Report]