Rebound Hammer Concrete Strength: JGJ/T 23 Conversion
How the Rebound Hammer Method Works
The rebound hammer strikes the concrete surface and the rebound value reflects surface hardness; combined with carbonation depth it is converted to estimated compressive strength through a strength curve, making it a common non-destructive test for concrete. Test areas are selected on the cast side of a member, at least 10 areas per member with 16 readings per area; after removing the 3 highest and 3 lowest readings, the remaining 10 are averaged. Areas must avoid dense rebar and defective zones so the values represent the real surface quality.
How Rebound Values Are Corrected
No correction is needed when the hammer strikes a side face horizontally. Non-horizontal striking (upward or downward) needs an angle correction, striking the cast top or bottom face needs a casting surface correction, and carbonation requires a table correction by carbonation depth. JGJ/T 23 provides the three correction tables (angle, casting surface and carbonation depth), which are built into the tool so the correction is applied automatically from the test area information.
How Strength Is Converted and Estimated
The corrected average rebound value is entered into the strength curve (the appendix curve of JGJ/T 23, or a regional or special curve) to get the test area strength. The member estimated strength is determined from the distribution of test area strengths: the minimum value for 10 to 14 areas, or a statistical estimate for 15 or more areas. The tool outputs each area strength and the member estimate; choose a curve that matches the concrete strength range and be cautious outside its scope.
Precautions
The rebound method suits normal concrete with sound surface quality (strength of about 10 to 60 MPa) and does not apply to members with loose, frozen or chemically corroded surfaces; clean and smooth the surface before testing. When the estimated strength seems low, combine with drilled cores for correction, and record the standard basis, instrument number and correction parameters in the report so the test is traceable. The tool works online and can add an AI interpretation of results.