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

Scope & Key Specifications from IS 1121 (Part 1) - 1974

• Scope: Methods for determining compressive strength of natural building stones.
• Test Piece Size & Shape (Clause 6.6): Size and shape must be clearly indicated.
• Preparation Description (Clause 6.7): Detailed description of test piece preparation to be included.

Key Formula for Compressive Strength Correction (Clause 6.2)

When height-to-diameter (or lateral dimension) ratio differs from 1 by ≥ 25%, use:

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

• (C_c) = Compressive strength of standard test piece (height = diameter)
• (C_p) = Compressive strength of specimen tested
• (b) = Diameter or lateral dimension
• (h) = Height of specimen

Notes:

• This formula corrects strength values to a standard specimen shape.
• Test pieces should conform to standard dimensions for valid results.
• Preparation method impacts test accuracy; document it thoroughly.

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

This ensures consistent, comparable compressive strength values across different specimen sizes.

IS 1121 Part 1: Selection of Samples for Compressive Strength Testing of Natural Stones

Key Specifications from Clauses:

• Clause 2.1:

  • Samples must represent the true average quality of the stone type or grade.

• Clause 2.2:

  • Samples are taken either from quarried stone or natural rock.
  • Sample size must be adequate to prepare the required number of test specimens.

• Clause 6.6:

  • The size and shape of test pieces must be clearly indicated.

Practical Guidelines:

Notes on Sampling:

• Ensure homogeneity by avoiding weathered or fractured parts.
• Samples should be marked and preserved properly before testing.

Summary Diagram:

flowchart TD
    A[Select Quarry/Natural Rock] --> B[Random Sampling]
    B --> C[Ensure True Average Quality]
    C --> D[Collect Adequate Size Sample]
    D --> E[Prepare Test Pieces (Cubic/Cylindrical)]
    E --> F[Conduct Compressive Strength Test]

This ensures reliable, representative compressive strength results per IS 1121 (Part 1).

IS 1121 Part 1: Test Pieces and Conditioning – Key Points

1. Size and Shape of Test Pieces (Clause 6.6)

• The size and shape must be clearly indicated.
• Typical test pieces: cubes, cylinders, or cores depending on the test.

2. Conditioning of Test Pieces

3. Sample Selection (Clause 2.2.2)

• Inspect quarry site thoroughly.
• Select separate samples for each stone class based on visual inspection.

Summary Table of Conditioning:

flowchart TD
    A[Test Pieces] --> B{Conditioning}
    B --> C[Saturated]
    B --> D[Dry]
    C --> E[Water immersion 20-30℃ for 72h]
    D --> F[Oven dry 105±5℃ for 24h]
    F --> G[Cool in desiccator 20-30℃]

Note: Proper conditioning ensures consistent and comparable test results for stone strength and durability.

IS 1121 Part 1: Testing Machine and Apparatus - Key Specifications

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

• Must have sufficient capacity for the test load.
• Load applied at specified rate (controlled).
• Equipped with two steel bearing plates with hardened faces:
  • One plate with spherical ball seating (centre coincides with plate face centre) to allow free rotation and slight tilting.
  • Other plate is a plain rigid bearing block.
• Bearing faces larger than nominal test piece size.
• Flatness tolerance of bearing surfaces: max deviation 0.0125 mm.

2. Test Pieces (Clause 3.1 & 6.6):

• Shape: Cubes or cylinders.
• Minimum lateral dimension/diameter: 50 mm.
• Height to diameter ratio: ≥ 1:1.
• Preparation method must be documented (Clause 6.7).

Summary Table: Test Piece Dimensions

Diagram: Compression Plate Setup

graph TD
    A[Upper Compression Plate]
    B[Ball Seating (Spherical)]
    C[Test Piece]
    D[Plain Rigid Bearing Plate]
    
    A --> B --> C --> D

Note: Proper alignment and bearing plate conditions are critical for valid compressive strength test results as per IS 1121 (Part 1).

IS 1121 Part 1 — Test Procedure Key Points

Test Piece Specifications (Clauses 3.1, 6.6, 6.7)

• Shape & Size: Cubes or cylinders.
• Minimum dimension: ≥ 50 mm (diameter or lateral face).
• Height to diameter/lateral dimension ratio: ≥ 1:1.
• Preparation: Test pieces must be cut or drilled from samples; details of preparation must be documented.

Testing Machine Requirements (Clause 4.1)

• Capacity: Sufficient for the test load.
• Load application: At specified rate.
• Bearing plates:
  • Two steel plates with hardened faces.
  • One plate with spherical seating to allow rotation and tilt.
  • Other plate plain and rigid.
  • Bearing faces larger than test piece size.
  • Flatness tolerance: max deviation 0.0125 mm.

Summary Table of Test Piece Dimensions

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

This ensures uniformity and reliability in compressive strength testing per IS 1121 Part 1.

IS 1121 Part 1: Evaluation and Report of Test Results

Key Specifications & Formulas:

• Load Application (Clause 5.1):
  Load shall be applied without shock, increasing continuously at approx.
  [ \textbf{Rate} = 140 \text{ kg/cm}^2 \text{ per minute} ]
  until failure. Record the maximum load and note failure type and stone appearance.

• Test Piece Details (Clause 6.6 & 6.7):

  • Indicate size and shape of test pieces.
  • Describe the preparation method of test pieces.

• Compressive Strength Calculation (Clause 6.3):
  Average compressive strength from three tests:
  [ f_c = \frac{P_{\max}}{A} ]
  where:

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

• Reporting:

  • Include average strength, specimen details, preparation method, failure mode, and any unusual observations.

Summary Table for Reporting

flowchart TD
    A[Start Test] --> B[Apply Load at 140 kg/cm²/min]
    B --> C{Failure Occurs?}
    C -- No --> B
    C -- Yes --> D[Record Max Load & Note Failure]
    D --> E[Calculate Compressive Strength]
    E --> F[Report Results with Specimen Details]
    F --> G[End]

This ensures consistent, standardized evaluation and reporting per IS 1121 Part 1.

IS 1121 (Part 1) - 1974: Amendments and Revisions Key Points

• Amendment No. 1 (Sept 1980) is incorporated in Edition 2.1 (2008-09).

• The amendment modifies Clause 3.1 (details not specified here).

• Clause 6.7 requires a description of test piece preparation in reports.

• Results rounding must follow IS 2:1960 rules.

• For compressive strength correction when height/diameter ratio deviates ≥ 25%:

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

  Where:

  • (C_c) = compressive strength of standard test piece (height = diameter)
  • (C_p) = compressive strength of specimen with height > diameter
  • (b) = diameter or lateral dimension
  • (h) = height

• The standard is split into four parts for specific properties, Part I covers compressive strength.

Summary Table: Amendments

Notes:

• Always refer to the latest edition for updated amendments.
• The standard is protected under BIS copyright; use details only for implementation.

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

For detailed test procedures and full amendment text, consult the official BIS publication.