About this tool Calculate tensile or bond strength from pull-off test results. Enter the failure load and dolly diameter — the tool calculates the stress at failure and assesses it against BS EN 1504-3 criteria for structural and non-structural concrete repair.
Optionally record the failure mode (adhesive at interface, cohesive within coating, cohesive within substrate, or adhesive at dolly). The failure mode is as important as the strength value — substrate failure indicates the bond exceeds the concrete tensile strength.
Per BS EN 1542 (test method) and BS 1881-207. Assessment thresholds follow BS EN 1504-3 (minimum 1.5 MPa for structural repair products).
How to use this tool 1. Enter the failure load in kN — from the pull-off tester gauge.
2. Select the dolly diameter — 50 mm is standard. 20 mm and 75 mm are also available.
3. Optionally select the failure mode — record where the failure occurred for the test report.
Technical information Strength (MPa) = Load (N) / Area (mm²)
Area = π × (d/2)² where d is the dolly diameter. For a 50 mm dolly, area = 1963 mm².
BS EN 1504-3 minimum: 1.5 MPa for structural repair, 0.8 MPa for non-structural. BRE Digest 444 suggests ≥ 1.0 MPa for adequate substrate.
Limitations Pull-off strength is highly sensitive to test preparation — core cutting depth, adhesive application, alignment, and loading rate all affect results. Follow BS EN 1542 procedure strictly.
Results from tests where failure occurs at the adhesive/dolly interface (Mode D) or adhesive/surface interface (Mode E) should be treated as invalid — the bond strength exceeds the measured value.
The assessment thresholds are general guidance. Specific acceptance criteria should be defined in the project specification or repair strategy.
Revision history 11 August 2026: Initial release
Disclaimer This tool is provided for educational and general information purposes only. It is not a substitute for professional engineering advice, design or verification.
Diggy and its contributors are not licensed engineering consultants and no results generated by this tool should be used directly for construction, design or safety-critical decisions.
All values and outputs are based on published empirical correlations and should be independently checked and confirmed by a qualified geotechnical engineer before use.
By using this tool, you accept full responsibility for how you interpret and apply the information provided.
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