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

IS 2770 Part 1: Introduction - Key Points, Formulas & Tables

1. Nominal Size of Deformed Bars (Clause 5.2.1)

• Nominal size = diameter or side of a plain bar with the same weight per meter as the deformed bar (per IS 1139-1966).
• Used to calculate surface area for bond tests.

2. Test Specimen Size (Clause 3.1)

• Bar embedded centrally, projecting 10 mm below cube bottom.
• Bar length above cube sufficient for gripping and loading.

3. Record of Results (Clause 6.1)

• Concrete cube crushing strength at test age.
• Age of specimen.
• Load at slip of 0.025 mm and 0.25 mm at free end.
• Slips at free and loaded ends during loading.
• Maximum load at failure and failure type.

4. Bond Strength Notes

• No standard quantitative definition.
• Load-slip curves preferred for comparison.
• Load at 0.025 mm slip is a good comparative metric.

Typical Bond Test Setup (Fig. 1 Summary)

• Concrete cube with embedded bar.
• Dial gauge with 0.0025 mm sensitivity measures slip.
• Slotted and spherical bearing blocks for load transfer.
• Rubber gasket and pipe sleeves for proper seating.

flowchart TD
    A[Concrete Cube] --> B[Embedded Reinforcing Bar]
    B --> C[Load Application]
    C --> D[Slip Measurement by Dial Gauge]
    D --> E[Record Load vs Slip Data]

For detailed procedures and reporting, follow IS 2770 Part 1 and IS 456 guidelines.

IS 2770 Part 1 - Scope: Key Specifications & Tables

1. Nominal Size of Deformed Bars (Clause 5.2.1)

• Surface area is calculated based on nominal size of the deformed bar.
• Nominal size = diameter or side of a plain bar with the same weight per meter as the deformed bar (per IS 1139-1966).

2. Test Specimen Size (Clause 3.1)

• Bars embedded vertically, projecting 10 mm below cube bottom.
• Length above cube sufficient for gripping and loading.

3. Record of Results (Clause 6.1)

• Concrete cube crushing strength (at test age)
• Age of specimen
• Load at slip of 0.025 mm and 0.25 mm
• Slips at free and loaded ends during loading
• Maximum load at failure & failure type

4. Tamping Rod (Clause 2.4)

• Round steel rod, 15 mm diameter, ~0.6 m length
• Hemispherical tip, 15 mm diameter

This ensures standardized testing for bond strength of reinforcement in concrete.
For detailed apparatus setup, refer to Fig.1 in IS 2770 Part 1.

flowchart TD
    A[Deformed Bar] --> B[Nominal Size (IS 1139)]
    B --> C[Calculate Surface Area]
    C --> D[Test Specimen Preparation]
    D --> E{Bar Diameter}
    E -->|≤12 mm| F[Cube 100 mm]
    E -->|>12 to ≤25 mm| G[Cube 150 mm]
    E -->|>25 mm| H[Cube 225 mm]
    F & G & H --> I[Embed Bar Vertically]
    I --> J[Testing & Record Results]

Let me know if you need formulas for bond stress or further details!

IS 2770 Part 1 — Apparatus Specifications and Key Tables

1. Tamping Rod (Clause 2.4)

• Material: Round, straight steel rod
• Diameter: 15 mm
• Length: ~0.6 m
• Tip: Hemispherical, 15 mm diameter

2. Measuring Apparatus (Clause 2.2)

• Used to measure relative movement of reinforcing bar and concrete at both loaded and unloaded ends.
• Dial micrometers with a least count of 0.0025 mm are recommended.

3. Test Specimens (Clause 3.1)

• Reinforcing bar embedded vertically with ~10 mm projection below 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 (0.0025 mm)
• Slotted steel bearing block
• Spherical seated bearing block
• 6 mm rubber gasket
• Round pipe sleeves (2 mm wall thickness)

flowchart LR
    A[Test Specimen: Concrete Cube] --> B[Embedded Reinforcing Bar]
    B --> C[Projection below cube: 10 mm]
    B --> D[Projection above cube: For gripping]
    A --> E[Tamping Rod: 15 mm dia, 0.6 m length]
    A --> F[Dial Gauge: 0.0025 mm]
    F --> G[Measures bar movement at loaded/unloaded ends]

This apparatus ensures precise measurement of bond strength between concrete and reinforcement.

IS 2770 Part 1: Test Specimens Key Points

1. Size of Test Specimens (Clause 3.1)

• Each specimen is a concrete cube with a single reinforcing bar embedded vertically.
• Bar projects 10 mm below the cube bottom and extends sufficiently above the cube for gripping/loading.

2. Preparation of Specimen (Clause 3.2)

• Use a tamping rod:
  • Diameter: 15 mm
  • Length: 0.6 m
  • Rounded hemispherical tip (15 mm diameter) for compaction.

3. Number of Specimens (Clause 3.3)

• Minimum 3 specimens for deformed bars.
• Minimum 3 specimens for plain bars (same cross-sectional area) for comparison.

Summary Diagram of Specimen Setup

graph TD
    A[Concrete Cube] -->|Embed| B[Reinforcing Bar]
    B -->|Project 10 mm below| C[Cube Bottom]
    B -->|Extend above| D[Gripping & Loading]
    E[Tamping Rod] -->|Compact Concrete| A

This ensures standardized specimen size and preparation for bond strength testing per IS 2770 Part 1.

IS 2770 Part 1: Test Procedure Key Points

Test Specimens (Clause 3.1)

• Cube sizes based on bar diameter:

• Bars embedded vertically, projecting ~10 mm below cube bottom and sufficiently above top for gripping.

Tamping Rod (Clause 2.4)

• Round, straight steel rod
• Diameter: 15 mm
• Length: approx. 0.6 m
• Rounded hemispherical tip, 15 mm diameter

Specimen Preparation (Clause 3.2 & 3.4)

• Top surface capped with:
  • Thin layer of neat cement paste (≥24 h before test), or
  • Thin layer of high-strength gypsum plaster (≥2 h before test)
• Align bar vertically using carpenter’s level and shims.
• Use 20 mm drilled steel plate for capping; press firmly and level.
• Remove excess capping material from drilled hole before hardening.

Testing Setup (Fig. 1 Summary)

• Use spherical seated bearing block, slotted steel bearing block, 0.0025 mm dial gauge
• Rubber gasket, round pipe sleeves brazed to cross bar for load application

Summary Diagram of Specimen Preparation:

flowchart TD
    A[Prepare Cube with Embedded Bar] --> B[Align Bar Vertically]
    B --> C[Apply Capping Material]
    C --> D[Press 20 mm Drilled Steel Plate]
    D --> E[Level Plate with Carpenter's Level]
    E --> F[Remove Excess Material]
    F --> G[Specimen Ready for Testing]

This ensures uniformity and accuracy in bond strength testing as per IS 2770 Part 1.

Calculation of Bond Stress (IS 2770 Part 1)

Key Formula (Clause 5.2):

[ \text{Average Bond Stress}, \tau = \frac{P}{\pi \times d \times l} ]

• (P) = Load at specified slip (N)
• (d) = Diameter of the reinforcing bar (mm)
• (l) = Embedded length of the bar (mm)
• (\pi d l) = Surface area of embedded length

Slip Values for Load Measurement (Clause 4.4):

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

Test Specimen Sizes (Clause 3.1):

Notes:

• Bond stress from tests is an average and not directly comparable to permissible bond stress in IS 456 Table VI.
• Load-slip curves are recommended for detailed comparison.
• Testing apparatus includes concrete cube with embedded bar, dial gauge (0.0025 mm sensitivity), and bearing blocks (see Fig. 1 in IS 2770 Part 1).

flowchart LR
    A[Apply Load P] --> B[Measure Slip at Free End]
    B --> C{Slip = 0.025 mm or 0.25 mm?}
    C -->|Yes| D[Calculate Bond Stress]
    D --> E[Average Bond Stress = P / (π × d × l)]

This concise summary provides the essential formulas, specimen sizes, and test slip criteria per IS 2770 Part 1 for bond stress calculation.

IS 2770 Part 1: Record of Results - Key Specifications

1. Surface Calculation for Deformed Bars (Clause 5.2.1)

• Surface area is calculated from nominal size of the deformed bar.
• Nominal size = diameter or side of a plain bar with the same weight per meter as the deformed bar (per IS 1139-1966).

2. Record of Results (Clause 6.1)

The following must be recorded systematically:

3. Additional Notes

• Maximum load for each failure type must be recorded (Clause 4.3.1.1).
• Tamping rod specifications: 15 mm diameter, ~0.6 m length, hemispherical tip (Clause 2.4).

Summary Table for Record of Results

This ensures consistent data for pull-out tests in concrete reinforcement evaluation.

IS 2770 Part 1 - Notes and Recommendations: Key Points

1. Nominal Size of Deformed Bars (Clause 5.2.1)

• Surface area for deformed bars is calculated based on nominal size.
• Nominal size = diameter of plain bar with same weight per meter as the deformed bar (per IS 1139-1966).

2. Test Specimen Size (Clause 3.1)

• Bar projects ~10 mm below cube bottom.
• Adequate length above cube for gripping and load application.

3. Record of Results (Clause 6.1)

Record these during pull-out tests:

• Concrete cube crushing strength at test age.
• Specimen age.
• Load at slip = 0.025 mm and 0.25 mm (free end).
• Slips at free and loaded ends at intervals.
• Maximum load at failure and failure type.

4. Important Notes (Clauses 0.3.1 & 0.4)

• Average bond stresses from tests do not directly correlate with permissible bond stresses in IS 456.
• Bond strength lacks a standard quantitative definition.
• Load at slip 0.025 mm is a preferred comparison metric for bond effectiveness.

Summary Diagram: Pull-out Test Setup

graph LR
A[Concrete Cube] --> B[Reinforcing Bar]
B --> C[Load Applied]
A --> D[Dial Gauge measures slip]
C --> E[Load-Slip Curve]

For detailed test procedures and apparatus, refer to Fig.1 of IS 2770 Part 1.