Methods of test for determination of strength properties of natural building stones, Part I: Compressive strength
1974 Edition

Scope & Principal Guidelines as per IS 1121 Part 1 (1974)

• Scope: Procedures for determining the compressive strength of natural construction stones.
• Specimen Dimensions (Clause 6.6): Exact size and shape must be specified.
• Preparation Details (Clause 6.7): Comprehensive description of specimen preparation required.

Correction Formula for Compressive Strength (Clause 6.2)

When the height-to-diameter (or lateral) ratio varies by 25% or more from unity:

[ C_c = \left[0.778 + 0.222 \times \frac{b}{h}\right] C_p ]

• (C_c): Corrected compressive strength for standard specimen (height = diameter)
• (C_p): Measured compressive strength of test specimen
• (b): Diameter or lateral dimension
• (h): Height of specimen

Notes:

• This formula standardizes strength values to a uniform specimen shape.
• Specimens must conform to standard sizes for valid comparisons.
• Preparation techniques influence test accuracy and must be well documented.

flowchart TD
    A[Specimen] --> B{Height/Diameter Ratio}
    B -- Ratio ≈ 1 --> C[Use Measured Strength]
    B -- Ratio ≥ 1.25 or ≤ 0.75 --> D[Apply Correction Formula]
    D --> E[Calculate Corrected Strength \(C_c\)]

This approach guarantees consistent compressive strength values across various specimen dimensions.

IS 1121 Part 1: Guidelines for Sampling Natural Stones for Strength Testing

Relevant Clauses:

• Clause 2.1:

  • Samples should represent the average quality of the stone type/grade.

• Clause 2.2:

  • Samples may be sourced from quarried stone or natural rock outcrops.
  • The sample size must be sufficient to prepare the required number of test specimens.

• Clause 6.6:

  • Test specimen dimensions and shapes must be clearly documented.

Practical Recommendations:

Additional Guidelines:

• Avoid weathered, fractured, or altered stone portions.
• Samples must be properly labeled and stored prior to testing.

Process Flowchart:

flowchart TD
    A[Choose Quarry or Rock Face] --> B[Perform Random Sampling]
    B --> C[Ensure Representative Average Quality]
    C --> D[Collect Adequate Sample Size]
    D --> E[Prepare Test Specimens (Cube/Cylinder)]
    E --> F[Conduct Compressive Strength Tests]

Following these steps helps achieve reliable and representative compressive strength results in accordance with IS 1121 (Part 1).

IS 1121 Part 1: Specimen Preparation and Conditioning Highlights

1. Specimen Size and Shape (Clause 6.6)

• Clearly specify size and geometry.
• Common specimen shapes include cubes, cylinders, or cores.

2. Conditioning Requirements

3. Sample Inspection (Clause 2.2.2)

• Examine quarry face carefully.
• Separate samples for each stone category based on visual assessment.

Conditioning Summary Table:

flowchart TD
    A[Test Specimens] --> B{Conditioning}
    B --> C[Saturated]
    B --> D[Dry]
    C --> E[Water Immersion at 20-30°C for 72h]
    D --> F[Oven Dry at 105±5°C for 24h]
    F --> G[Cooling in Desiccator at 20-30°C]

Proper conditioning is vital to ensure consistent and comparable compressive strength measurements.

IS 1121 Part 1: Specifications for Testing Apparatus

1. Testing Machine Capacity and Load Application (Clause 4.1):

• Machine must support the required test load.
• Load applied at a controlled, specified rate.
• Equipped with two steel bearing plates with hardened surfaces:
  • One plate fitted with a spherical ball seating allowing free rotation and slight tilt, centered on the plate face.
  • The other plate is a flat rigid bearing block.
• Bearing surfaces must exceed the nominal specimen size.
• Maximum allowable flatness deviation of bearing surfaces: 0.0125 mm.

2. Test Specimen Requirements (Clauses 3.1 & 6.6):

• Shapes: Cubic or cylindrical.
• Minimum lateral dimension or diameter: 50 mm.
• Height-to-diameter ratio: at least 1:1.
• Specimen preparation method must be documented (Clause 6.7).

Test Specimen Dimension Summary

Compression Plate Arrangement

graph TD
    A[Upper Compression Plate]
    B[Spherical Ball Seating]
    C[Test Specimen]
    D[Flat Rigid Bearing Plate]

    A --> B --> C --> D

Correct alignment and condition of bearing plates are crucial for valid compressive strength measurements as per IS 1121 Part 1.

IS 1121 Part 1: Procedure for Compressive Strength Testing

Specimen Details (Clauses 3.1, 6.6, 6.7)

• Shape: Cubes or cylinders.
• Minimum lateral dimension: 50 mm.
• Height-to-lateral dimension ratio: minimum 1:1.
• Specimens must be cut or drilled from samples; preparation details recorded.

Testing Machine Requirements (Clause 4.1)

• Capacity adequate for expected loads.
• Load applied at specified, controlled rate.
• Bearing plates:
  • Two steel plates with hardened faces.
  • One with spherical seating for rotation and tilt.
  • One plain rigid plate.
  • Bearing area larger than specimen face.
  • Flatness tolerance: max deviation 0.0125 mm.

Summary Table: Specimen Dimensions

flowchart LR
    A[Sample] --> B[Cut/Drill Specimen]
    B --> C{Shape}
    C -->|Cube| D[Dimension ≥ 50 mm]
    C -->|Cylinder| D
    D --> E[Height ≥ Diameter]
    E --> F[Position Between Bearing Plates]
    F --> G[Apply Load at Controlled Rate]

This ensures standardized and reliable compressive strength testing as per IS 1121 Part 1.

IS 1121 Part 1: Guidelines for Evaluation and Reporting

Key Points and Formulas:

• Load Application (Clause 5.1):

  • Load must be applied smoothly, without shock.
  • Loading rate approximately:

  [ 140 \text{ kg/cm}^2 \text{ per minute} ]

• Specimen Details (Clauses 6.6 & 6.7):

  • Clearly specify specimen size and shape.
  • Provide detailed description of preparation.

• Compressive Strength Calculation (Clause 6.3):

  [ f_c = \frac{P_{max}}{A} ]

  where:

  • (P_{max}) = maximum load at failure (Newtons or kgf)
  • (A) = cross-sectional area of specimen (mm² or cm²)

• Reporting:

  • Report average compressive strength from at least three specimens.
  • Include specimen details, preparation method, failure mode, and any notable observations.

Reporting Summary Table

flowchart TD
    A[Begin Test] --> B[Apply Load at 140 kg/cm²/min]
    B --> C{Failure Occurs?}
    C -- No --> B
    C -- Yes --> D[Record Maximum Load and Failure Mode]
    D --> E[Calculate Compressive Strength]
    E --> F[Compile and Report Results]
    F --> G[End of Test]

This procedure ensures uniform evaluation and reporting consistent with IS 1121 Part 1.

IS 1121 (Part 1) - 1974: Amendments and Updates Overview

• Amendment No. 1 (September 1980): Integrated into Edition 2.1 (2008-09).

• Modified Clause 3.1 (specific changes not detailed here).

• Mandates description of specimen preparation in test reports (Clause 6.7).

• Numerical results must be rounded according to IS 2:1960.

• Correction formula for compressive strength when specimen height-to-diameter ratio deviates by 25% or more:

  [ C_c = 0.778 + 0.222 \times \frac{b}{h} \times C_p ]

  Where:

  • (C_c) = corrected standard compressive strength (height = diameter)
  • (C_p) = measured strength of specimen
  • (b) = diameter or lateral dimension
  • (h) = specimen height

• The overall standard is divided into four parts addressing various stone properties; Part I addresses compressive strength.

Amendment Summary Table

Summary Flowchart

flowchart LR
    A[IS 1121 Part 1: Compressive Strength] --> B[Amendment No. 1 (1980)]
    B --> C[Revision of Clause 3.1]
    B --> D[Specimen Preparation Description (Clause 6.7)]
    A --> E[Correction Formula for Height-Diameter Ratio]

For comprehensive procedures and amendment details, refer to the official BIS documentation.