Methods of testing bond in reinforced concrete, Part 1: Pull-out test
1967 Edition

Overview of Pull-Out Test Procedure - Essential Concepts, Formulas & Data Tables

1. Nominal Diameter of Deformed Reinforcement (Clause 5.2.1)

• Defined as the diameter or side length of a smooth bar with equivalent weight per meter as the deformed bar (per IS 1139-1966).
• Used to determine the effective surface area for bond assessment.

2. Dimensions of Test Specimens (Clause 3.1)

• Bars positioned centrally with 10 mm projection below the cube.
• Sufficient bar length above the cube for gripping and load application.

3. Documentation of Test Data (Clause 6.1)

• Concrete cube compressive strength at testing age.
• Specimen age at testing.
• Loads corresponding to slips of 0.025 mm and 0.25 mm at the free end.
• Recorded slips at both loaded and free ends during loading.
• Maximum failure load and nature of failure.

4. Bond Strength Considerations

• No fixed numeric definition of bond strength exists.
• Load-slip curves are preferred for comparative evaluation.
• Load at 0.025 mm slip serves as a reliable comparative parameter.

Common Test Setup (Fig. 1 Synopsis)

• Concrete cube containing embedded reinforcing bar.
• Dial gauge with 0.0025 mm precision for slip measurement.
• Slotted and spherical bearing blocks to transfer loads.
• Rubber gasket and pipe sleeves ensure correct seating.

flowchart TD
    Cube[Concrete Cube] --> Bar[Embedded Reinforcing Bar]
    Bar --> Load[Load Application]
    Load --> Slip[Slip Measurement via Dial Gauge]
    Slip --> Record[Log Load-Slip Data]

For comprehensive procedures and reporting methods, refer to IS 2770 Part 1 and IS 456.

Scope of the Pull-Out Test Method (IS 2770 Part 1): Key Specifications & Tables

1. Nominal Diameter of Deformed Bars (Clause 5.2.1)

• Surface area calculation is based on the nominal diameter.
• Nominal diameter corresponds to a plain bar diameter having identical weight per meter as the deformed bar (per IS 1139-1966).

2. Specimen Size Requirements (Clause 3.1)

• Bars embedded vertically with 10 mm projection below cube bottom.
• Adequate bar length above cube for gripping and loading.

3. Data Recording Criteria (Clause 6.1)

• Concrete cube compressive strength at test age.
• Specimen age.
• Loads at slips of 0.025 mm and 0.25 mm at free end.
• Slips at loaded and free ends throughout loading.
• Maximum failure load and failure mode.

4. Tamping Rod Details (Clause 2.4)

• Round steel rod, 15 mm diameter, approximately 0.6 m length.
• Hemispherical tip with 15 mm diameter.

This ensures consistency in testing bond strength of reinforcement in concrete. Refer to Fig. 1 in IS 2770 Part 1 for apparatus details.

flowchart TD
    Bar[Deformed Bar] --> Nominal[Determine Nominal Size (IS 1139)]
    Nominal --> Surface[Calculate Surface Area]
    Surface --> Specimen[Prepare Test Specimen]
    Specimen --> Diameter{Bar Diameter}
    Diameter -->|≤12 mm| Cube100[Cube 100 mm]
    Diameter -->|>12 to 25 mm| Cube150[Cube 150 mm]
    Diameter -->|>25 mm| Cube225[Cube 225 mm]
    Cube100 & Cube150 & Cube225 --> Embed[Embed Bar Vertically]
    Embed --> Test[Conduct Test and Record Data]

Please ask if bond stress formulas or additional details are needed.

Equipment Specifications as per IS 2770 Part 1

1. Tamping Rod (Clause 2.4)

• Constructed from round, straight steel.
• Diameter: 15 mm.
• Length: approximately 0.6 meters.
• Rounded hemispherical tip with 15 mm diameter.

2. Measuring Instruments (Clause 2.2)

• Used to gauge relative displacement between reinforcing bar and concrete at both loaded and unloaded ends.
• Dial micrometers with minimum graduation of 0.0025 mm are recommended.

3. Test Specimens (Clause 3.1)

• Reinforcing bar embedded vertically with about 10 mm extension below the cube.
• Bar length above cube sufficient for gripping and load application.

4. Typical Apparatus Components (Fig. 1)

• Concrete cube with embedded reinforcing bar.
• Dial gauge with 0.0025 mm sensitivity.
• Slotted steel bearing block.
• Spherical bearing block.
• 6 mm thick rubber gasket.
• Round pipe sleeves with 2 mm wall thickness.

flowchart LR
    Specimen[Concrete Cube Specimen] --> Bar[Embedded Reinforcing Bar]
    Bar --> ProjectionBelow[10 mm Projection Below Cube]
    Bar --> ProjectionAbove[Extended Length Above Cube]
    Specimen --> TampingRod[Tamping Rod: 15 mm dia, 0.6 m length]
    Specimen --> DialGauge[Dial Gauge: 0.0025 mm Graduation]
    DialGauge --> Measure[Measures Movement at Both Ends]

This setup allows precise measurement of bond strength between reinforcement and concrete.

Key Aspects of Test Specimens (IS 2770 Part 1)

1. Specimen Dimensions (Clause 3.1)

• Specimens are concrete cubes with a single reinforcing bar positioned vertically.
• Bar projects 10 mm below the cube bottom and extends sufficiently above for gripping and loading.

2. Specimen Fabrication (Clause 3.2)

• Utilize a tamping rod:
  • Diameter: 15 mm
  • Length: 0.6 m
  • Hemispherical tip of 15 mm diameter for consolidation.

3. Specimen Quantity (Clause 3.3)

• Minimum of three specimens each for deformed and plain bars (with equivalent cross-sectional area) to facilitate comparison.

Specimen Setup Diagram

graph TD
    Cube[Concrete Cube] --> Embed[Embed Reinforcing Bar Vertically]
    Embed --> ProjectBelow[Bar Projects 10 mm Below Cube]
    Embed --> ProjectAbove[Bar Extends Above Cube for Grip]
    TampingRod --> Compact[Compact Concrete During Casting]

These steps standardize specimen preparation for consistent bond strength evaluation.

Test Methodology Summary (IS 2770 Part 1)

Specimen Dimensions (Clause 3.1)

• Cube sizes depend on bar diameter:

• Bars embedded vertically with about 10 mm extension below cube bottom and sufficient length above for gripping.

Tamping Rod (Clause 2.4)

• Round steel rod
• Diameter: 15 mm
• Length: approximately 0.6 m
• Hemispherical tip, 15 mm diameter

Specimen Preparation (Clauses 3.2 & 3.4)

• Top bearing surface must be capped with either:
  • Thin layer of neat cement paste applied at least 24 hours before testing, or
  • Thin layer of high-strength gypsum plaster applied at least 2 hours prior.
• Bar alignment ensured vertical using carpenter’s level and shims.
• A 20 mm thick drilled steel plate (oiled) is pressed onto the capping layer and leveled.
• Excess capping material around the drilled hole is removed before hardening to facilitate plate removal.

Test Setup (Fig. 1 Summary)

• Assembly includes spherical bearing block, slotted steel bearing block, dial gauge with 0.0025 mm precision.
• Rubber gasket and brazed pipe sleeves on cross bar for proper load application.

Specimen Preparation Flowchart

flowchart TD
    PrepareCubeMold --> PositionBarVertically
    PositionBarVertically --> CastConcrete
    CastConcrete --> Cure
    Cure --> ApplyCappingMaterial
    ApplyCappingMaterial --> PressSteelPlate
    PressSteelPlate --> LevelPlate
    LevelPlate --> RemoveExcessMaterial
    RemoveExcessMaterial --> ReadyForTest

These steps ensure uniform specimen quality and accurate bond strength determination.

Bond Stress Calculation (IS 2770 Part 1)

Primary Formula (Clause 5.2):

[ \tau_{avg} = \frac{P}{\pi \times d \times l} ]

where:

• (P): Load at specified slip (Newtons)
• (d): Diameter of reinforcing bar (millimeters)
• (l): Embedded length of bar (millimeters)
• (\pi d l): Surface area over which bond acts

Slip Values for Load Recording (Clause 4.4):

• Load at 0.025 mm slip (free end)
• Load at 0.25 mm slip (free end)

Specimen Sizes (Clause 3.1):

Notes:

• The bond stress calculated is an average value and not directly comparable to permissible bond stresses in IS 456.
• Load-slip curves provide detailed comparative insight.
• Testing apparatus includes concrete specimen with embedded bar, dial gauge with 0.0025 mm sensitivity, and bearing blocks (see Fig. 1).

flowchart LR
    LoadApplied[P]
    LoadApplied --> MeasureSlip[Measure Slip at Free End]
    MeasureSlip --> CheckSlip{Slip = 0.025 mm or 0.25 mm?}
    CheckSlip -- Yes --> CalculateTau[Calculate Average Bond Stress]
    CalculateTau --> Formula[\tau = P / (\pi d l)]

This provides the essential calculation method and parameters for bond stress evaluation.

Guidelines for Recording Results (IS 2770 Part 1)

1. Surface Area Computation for Deformed Bars (Clause 5.2.1)

• Surface area calculation uses the nominal size of the deformed bar.
• Nominal size is defined as diameter or side of a plain bar with equal weight per meter as per IS 1139-1966.

2. Test Data to be Documented (Clause 6.1)

3. Additional Remarks

• Record maximum load separately for each failure mode (Clause 4.3.1.1).
• Tamping rod specifications: 15 mm diameter, ~0.6 m length with hemispherical tip (Clause 2.4).

Summary Table of Results

This ensures consistent and comprehensive data recording for pull-out tests.

Key Notes and Recommendations (IS 2770 Part 1)

1. Nominal Size for Deformed Bars (Clause 5.2.1)

• Surface area calculations must be based on nominal size.
• Nominal size equals diameter of a plain bar having the same weight per meter as the deformed bar (per IS 1139-1966).

2. Specimen Dimensions (Clause 3.1)

• Bars extend roughly 10 mm below the bottom of the cube.
• Length above cube allows for gripping and load application.

3. Required Data Recording (Clause 6.1)

• Concrete compressive strength at test age.
• Specimen age.
• Loads at slips of 0.025 mm and 0.25 mm (free end).
• Slip measurements at free and loaded ends during loading.
• Maximum load and failure mode.

4. Additional Remarks (Clauses 0.3.1 & 0.4)

• Average bond stresses from pull-out tests do not directly correspond to permissible bond stresses in IS 456.
• There is no universally accepted quantitative definition of bond strength.
• Load corresponding to 0.025 mm slip is a preferred comparative metric.

Pull-Out Test Setup Diagram

graph LR
    Cube[Concrete Cube] --> Bar[Reinforcing Bar]
    Bar --> Load[Applied Load]
    Cube --> Gauge[Dial Gauge for Slip Measurement]
    Load --> Curve[Load-Slip Curve Analysis]

Refer to Fig. 1 in IS 2770 Part 1 for detailed apparatus and testing procedure.