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

IS 6441 Part 2 - Scope & Key Specifications

Scope:

• Covers Determination of drying shrinkage of autoclaved cellular concrete products.
• Part of a 9-part series on test methods for autoclaved cellular concrete (see table below).

Key Formulas & Specifications for Drying Shrinkage (Clause 4.2.3 & 6.1)

• Shrinkage stabilization criterion:
  Two consecutive length measurements, 7 days apart, must differ by ≤ 0.007% of specimen length.

• Report must include:

  • Code designation
  • Product ID
  • Manufacture date
  • Sampling details (place, method, time)
  • Specimen size & age at test start
  • Linear shrinkage of each prism & mean value

Summary Diagram of Shrinkage Test Process

flowchart TD
    A[Prepare Specimens] --> B[Measure Initial Length]
    B --> C[Drying Period]
    C --> D[Measure Length Repeatedly]
    D --> E{Two readings 7 days apart differ ≤ 0.007%?}
    E -- No --> C
    E -- Yes --> F[Record Final Shrinkage]
    F --> G[Prepare Report as per Clause 6.1]

This concise scope and key points ensure compliance with IS 6441 Part 2 for drying shrinkage testing.

IS 6441 Part 2 (1972) - Key References and Specifications

Part Breakdown (from Foreword)

Reporting Requirements (Clause 6.1)

Test report must include:

• Code designation (IS 6441 Part II)
• Product identification
• Manufacture date
• Sampling place, method, time
• Specimen size & age at test start
• Linear shrinkage values (individual and mean)

Additional Notes

• The standard aligns with international practices but tailored for Indian conditions.
• Contact details for BIS regional and branch offices are provided for further clarifications.

Typical Formula for Linear Shrinkage (General Knowledge)

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

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

This is the key parameter measured under Part II.

flowchart TD
    A[Start: Sample Preparation] --> B[Measure Initial Length \(L_0\)]
    B --> C[Drying Period]
    C --> D[Measure Length at time \(t\) \(L_t\)]
    D --> E[Calculate Linear Shrinkage]
    E --> F[Report Results as per Clause 6.1]

For detailed test procedures and specimen sizes, refer to the full IS 6441 Part II document.

IS 6441 Part 2: Definitions & Key Specifications

• Scope: Part II covers the Determination of Drying Shrinkage of autoclaved cellular concrete (ACC) products.

• Key Definition:

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

• Measurement Protocol (Clause 4.2.3):

  • Length measurements are repeated until constant length is achieved.
  • Constant length = when two consecutive readings, taken 7 days apart, differ by ≤ 0.007% of specimen length.

• General Notes:

  • The standard aligns with international practices, ensuring relevance to Indian field conditions (Clause 0.3).
  • The test involves monitoring length changes of prisms under controlled drying.

Summary Table: Length Measurement Criterion for Drying Shrinkage

This ensures repeatability and accuracy in drying shrinkage determination for ACC products.

IS 6441 Part 2: Apparatus and Materials for Drying Shrinkage Measurement

Key Specifications for Measuring Instruments (Clause 3.1)

• Accuracy: ±0.003% of specimen length.
• Range: Must accommodate small gauge length variations.
• Contact: Positive contact with gauge plugs to ensure reproducibility.
• Calibration: Regular checks against a standard reference.

Measurement Conditions (Clauses 4.2.2 & 4.2.3)

• Temperature: 27 ± 2°C during measurement.
• Specimen Position: Consistent placement; take two readings at 0° and 90° rotation.
• Result: Use average if readings differ.
• Stability: Length considered stable when two readings 7 days apart differ by ≤0.007% of length.

Summary Table: Measurement Accuracy and Conditions

flowchart LR
    A[Specimen Preparation] --> B[Initial Length Measurement]
    B --> C{Rotate Specimen 90°?}
    C -- Yes --> D[Second Length Measurement]
    D --> E[Average Length]
    E --> F[Repeat Measurements Weekly]
    F --> G{Length Change ≤ 0.007%?}
    G -- No --> F
    G -- Yes --> H[Stable Length Achieved]

This ensures precise and reproducible drying shrinkage measurements as per IS 6441 Part 2.

IS 6441 Part 2: Preparation of Specimens for Drying Shrinkage Test

Key Specifications (Clause 2.3)

• Specimen Cutting: Use rotating carbo-rundum blades or similar for clean, plane cuts.
• Surface Planeness: Largest surface deviation ≤ 0.1 mm diagonally.
• Specimen Axis Orientation:
  • If sample height < 24 cm: length axis ⟂ to rise direction.
  • If sample height ≥ 24 cm: length axis ∥ to rise direction.

Water Saturation (Clause 4.1)

• Immerse prismatic specimens with gauge plugs in water until constant weight.
• Minimum immersion time: 72 hours.
• Specimens initially float if bulk density < 1 g/cm³; weigh down after 2 hours for full immersion.

Measurement Accuracy (Clause 3.1)

• Length measurement accuracy: 0.003% of specimen length.
• Instruments must:
  • Have sufficient range for gauge length variations.
  • Ensure positive contact with gauge plugs.
  • Be regularly calibrated against a standard.

Summary Table for Specimen Orientation

flowchart TD
    A[Large Sample Piece] --> B[Cut Specimens with Carbo-Rundum Blade]
    B --> C{Sample Height < 24 cm?}
    C -- Yes --> D[Length Axis ⟂ Rise Direction]
    C -- No --> E[Length Axis ∥ Rise Direction]
    D & E --> F[Check Surface Planeness ≤ 0.1 mm]
    F --> G[Attach Gauge Plugs]
    G --> H[Water Saturation: Immerse ≥ 72 h]
    H --> I[Measure Length with 0.003% Accuracy]

This ensures standardized specimen preparation for reliable drying shrinkage measurement as per IS 6441 Part 2.

IS 6441 Part 2: Test Procedure for Drying Shrinkage

Key Specifications & Procedures

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

• Specimen Positioning:
  Place specimens consistently in the measuring unit. Take two readings:

  • First reading
  • Second reading after rotating specimen 90° around its length axis
    Use the average if readings differ.

• Measuring Instrument Requirements (Clause 3.1):

  • Accuracy: 0.003% of specimen length
  • Adequate range for small gauge length variations
  • Positive contact with gauge plugs for reproducibility
  • Regular calibration against a standard reference

• Rounding Off Results:
  Follow IS 2-1960 for rounding final values.

Summary Table: Measurement Accuracy

flowchart LR
    A[Specimen Placement] --> B[First Measurement]
    B --> C[Rotate Specimen 90°]
    C --> D[Second Measurement]
    D --> E{Are readings equal?}
    E -- Yes --> F[Use reading]
    E -- No --> G[Average of two readings]
    F & G --> H[Report value (rounded as per IS 2-1960)]

This ensures precise, reproducible drying shrinkage measurements per IS 6441 Part 2.

IS 6441 Part 2: Measurement of Drying Shrinkage - Key Points

• Specimen Dimensions (Clause 2.1):

  • Cross-section: 40 mm x 40 mm (square prism)
  • Length: Minimum 150 mm (to fit measuring apparatus)

• Specimen Type:

  • Unreinforced prisms

• Drying Shrinkage Measurement:

  • Length change is measured over time as the specimen dries.
  • Shrinkage strain, ε_sh, is calculated as:
    [ \varepsilon_{sh} = \frac{\Delta L}{L_0} \times 10^6 \quad \text{(in microstrain, µε)} ]
    where:
    • (\Delta L = L_0 - L_t) (change in length)
    • (L_0) = initial length
    • (L_t) = length at time (t)

• Testing Environment:

  • Specimens are stored in controlled drying conditions (usually 50% RH, 23°C) after initial curing.

Summary Table: Specimen Dimensions

flowchart TD
    A[Prepare Concrete Prism] --> B[Initial Curing]
    B --> C[Measure Initial Length (L0)]
    C --> D[Drying in Controlled Environment]
    D --> E[Measure Length at Time t (Lt)]
    E --> F[Calculate Shrinkage Strain εsh = ((L0 - Lt)/L0)*10^6]

This method ensures consistent and comparable drying shrinkage data for concrete prisms per IS 6441 Part 2.

IS 6441 Part 2: Environmental Conditions Key Points

• Storage Room / Humidity Chamber (Clause 3.4):

  • Temperature: 27 ± 2°C
  • Relative Humidity: Maintained at equilibrium over a saturated potassium carbonate (K2CO3) solution.
  • Purpose: To dry specimens under controlled humidity and temperature.

• Measurement Conditions (Clause 4.2.2):

  • Temperature during measurements: 27 ± 2°C
  • Specimen positioning:
    • Place specimen consistently in the measuring unit.
    • Take two readings: first in initial position, second after rotating specimen 90° around its length axis.
    • Use the average if readings differ.

Saturated K2CO3 Solution Humidity Reference

• Provides about 43% relative humidity at 27°C (equilibrium condition).

Summary Table:

flowchart LR
    A[Specimen Storage] --> B[Humidity Chamber]
    B -->|Temp 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 Reading if Different]

This ensures consistent environmental conditions per IS 6441 Part 2 for accurate and repeatable specimen testing.

IS 6441 Part 2: Calculation and Expression of Results

Key Specifications from Clauses

• Length Stability (Clause 4.2.3):
  Repeated length measurements are taken until two consecutive readings, 7 days apart, differ by ≤ 0.007% of the specimen length. This confirms constant length.

• Measurement Accuracy (Clause 3.1):

  • Accuracy: ±0.003% of specimen length
  • Instrument range must cover small gauge length variations
  • Positive contact with gauge plugs for reproducibility
  • Regular calibration against a reference standard

• Rounding Off Results:
  Follow IS 2-1960 for rounding off final observed/calculated values.

Practical Formula for Length Change (%)

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

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

Summary Table: Measurement Criteria

flowchart TD
    A[Start Measurement] --> B[Measure Length L0]
    B --> C[Wait 7 Days]
    C --> D[Measure Length Lt]
    D --> E{Is |Lt - Lprev| ≤ 0.007% of L0?}
    E -- No --> C
    E -- Yes --> F[Length Constant Achieved]
    F --> G[Calculate Length Change %]
    G --> H[Report Results (Round per IS 2-1960)]

This ensures reliable and standardized length measurement and reporting per IS 6441 Part 2.

IS 6441 Part 2 - Reporting Requirements (Clause 6.1)

The test report for linear shrinkage of cement specimens must include:

• a) Code designation: Reference to the applicable IS code.
• b) Identification of product: Cement brand/type.
• c) Date of manufacture: When the cement was produced.
• d) Place, method, and time of sampling: Details on sampling procedure.
• e) Size and age of specimens at start of shrinkage test: Dimensions and curing age.
• f) Linear shrinkage: Individual prism shrinkage values and the mean shrinkage.

Additional Notes:

• Repeated length measurements continue until length stabilizes (two readings 7 days apart within 0.007% length difference).
• Rounding off results should follow IS 2-1960 guidelines.
• Linear shrinkage (%) is calculated as:

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

Where:

• (L_0) = initial length at start of test
• (L_t) = length at time (t)

Summary Table for Reporting

flowchart TD
    A[Start Test] --> B[Record Specimen Size & Age]
    B --> C[Measure Initial Length \(L_0\)]
    C --> D[Periodic Length Measurements \(L_t\)]
    D --> E{Are two readings 7 days apart within 0.007%?}
    E -- No --> D
    E -- Yes --> F[Calculate Shrinkage %]
    F --> G[Prepare Report with Clause 6.1 details]
    G --> H[End]

This ensures consistent, traceable, and standardized reporting per IS 6441 Part 2.

IS 6441 Part 2: Precision and Accuracy Key Points

1. Measurement Accuracy (Clause 3.1a)

• Accuracy must be 0.003% of specimen length.
• Example: For a 100 mm specimen, max error = 0.003 mm.

2. Measurement Repeatability (Clause 4.2.3)

• Two consecutive readings at 7-day intervals must be within 0.007% of specimen length.
• Ensures length stability before final measurement.

3. Measurement Procedure (Clause 4.2.2)

• Temperature controlled at 27 ± 2°C.
• Specimen placed consistently.
• Two readings taken: specimen rotated 90° around length axis.
• Use average if readings differ.

4. Instrument Requirements (Clause 3.1)

• Sufficient range for gauge length variation.
• Positive contact with gauge plugs for reproducibility.
• Regular calibration against a reference standard.

5. Reporting (Clause 0.5)

• Round off results as per IS 2-1960.

Summary Table: Accuracy & Repeatability

flowchart TD
    A[Start Measurement] --> B[Set Temperature 27±2°C]
    B --> C[Place specimen consistently]
    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[Re-measure]
    H --> J[Repeat after 7 days]
    J --> K{Difference ≤ 0.007%?}
    K -- Yes --> L[Accept measurement]
    K -- No --> I

This ensures precision (accuracy within 0.003%) and accuracy (repeatability within 0.007%) for length measurements per IS 6441 Part 2.

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

This part covers determination of drying shrinkage of autoclaved cellular concrete products.

Key Specifications & Reporting (Clause 6.1)

• Report must include:
  • Code designation
  • Product identification
  • Date of manufacture
  • Sampling details (place, method, time)
  • Specimen size and age at test start
  • Linear shrinkage of individual prisms & mean value

Important Notes on Measurement (Clause 4.2.3)

• Length measurements repeated until constant length is reached.
• Constant length = two consecutive readings (7 days apart) within 0.007% of specimen length.

Shrinkage Calculation (Clause 5)

• Linear Shrinkage (%) =
  [ \frac{L_0 - L_t}{L_0} \times 100 ] Where:
  • (L_0) = initial length at start of drying
  • (L_t) = length at time (t)

Summary Table: IS 6441 Parts Overview

This standard aligns with international practices and is tailored for Indian field conditions.

flowchart TD
    A[Start Shrinkage Test] --> B[Measure Initial Length (L0)]
    B --> C[Dry Specimen]
    C --> D[Measure Length at intervals (Lt)]
    D --> E{Is |Lt - previous Lt| < 0.007% of L0?}
    E -- No --> C
    E -- Yes --> F[Calculate Shrinkage %]
    F --> G[Report Results]