📘 What is the Pull-Out Test?
The Pull-Out Test is a semi-destructive test in civil engineering used to assess the in-situ compressive strength of concrete or the bond strength between reinforcement and concrete.
There are two major applications:
- Concrete Strength Estimation
- Anchorage/Bond Strength Testing (for rebars, anchors, or post-installed bolts)
🎯 Objectives:
- Determine in-place compressive strength of concrete.
- Evaluate bond strength between steel and concrete.
- Assess anchor performance for safety-critical applications.
- Validate quality of concrete in structural elements like slabs, columns, beams, footings, etc.
🧰 Apparatus Required:
- Pull-out test device with hydraulic jack or actuator
- Dial gauge or load cell to measure force/load
- Embedded or installed pull-out insert / rebar / anchor
- Reaction frame or bearing plate
- Support tripod or fixing system
🛠️ Test Procedure (General Overview):
A. Concrete Strength Pull-Out Test (LOK Test or CAPO Test):
- A metal insert is cast into the concrete during pouring.
- After curing, a pulling force is applied perpendicular to the concrete surface.
- The force required to dislodge the insert is recorded.
- This force is correlated with compressive strength using calibration curves.
B. Rebar or Anchor Pull-Out Test:
- Expose the rebar or install an anchor into the cured concrete.
- Connect the test setup to apply axial tension.
- Increase load steadily until:
- Slip occurs
- Pull-out occurs
- Failure of anchor/concrete
- Record the maximum load at failure.
📊 Results & Interpretation:
| Parameter Measured | Typical Outcome |
|---|---|
| Pull-out load (kN) | Indicates the force at failure/slip |
| Slip vs. load graph | Assesses ductility and bond behavior |
| Failure mode | Bond failure, rebar pull-out, concrete breakout |
| Equivalent compressive strength (for concrete inserts) | Estimated using calibration |
✅ Advantages:
- Reliable estimation of in-situ strength
- Assesses actual performance of anchors and reinforcement
- Helps in quality control and structural assessment
⚠️ Limitations:
- Semi-destructive (may damage small part of concrete)
- Requires calibration curves
- Not suitable for lightweight or low-strength concrete
- Needs careful alignment and reaction setup
📌 Standards / Guidelines:
- ASTM C900: Standard Test Method for Pullout Strength of Hardened Concrete
- IS 2770 (Part 1): Indian Standard for Bond Strength of Reinforcement
- EN 12504-3: Testing concrete in structures — Pull-out testing
🏗️ Applications:
- Concrete core strength validation
- Anchor bolt testing (e.g., façade fixing, MEP supports)
- Rebar anchorage pull-out tests
- Post-installed systems verification