How many impact readings are required for a single test result?

A minimum of 9 valid readings must be taken over the test area to calculate the median/mean rebound number.

What is the minimum distance allowed between two impact points?

Impact points must be at least 20 mm apart and 20 mm away from any edge.

Can the rebound hammer be used for acceptance of new concrete?

No, it is intended to check uniformity and relative strength, but cannot substitute standard cube tests for official acceptance without extensive correlation.

How often should the rebound hammer be calibrated?

It should be checked against a standard steel calibration anvil before and after every test sequence to ensure consistent spring performance.

IS 516 Part 5/Sec 3

: 2022

Methods of tests for strength of concrete - Part 5: Non-destructive testing of hardened concrete - Section 3: Rebound Hammer

CurrentFrequently UsedTesting MethodStructural Engineering · Testing Methods and Quality Control

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This code specifies the standard procedure for non-destructive testing of hardened concrete using a rebound hammer. Engineers use it to assess in-situ concrete uniformity, delineate zones of poor quality, and estimate relative compressive strength in existing structures.

Describes the procedure for assessing the surface hardness and estimating the strength of hardened concrete using a rebound hammer.

Quick Reference Values

Minimum readings per test area9 readings

Minimum distance between impact points20 mm

Minimum distance from edge of member20 mm

Minimum member thickness to avoid mass effect100 mm

Test area sizeApproximately 300 mm x 300 mm

Practical Notes

Rebound hammer readings are highly sensitive to surface conditions. Surface carbonation artificially inflates the rebound number, leading to an overestimation of strength.

Do not take readings directly over reinforcing bars with shallow cover, as the steel will cause abnormally high rebound numbers.

The rebound hammer provides only an approximate indication of strength. For structural assessment, it must always be correlated with drilled concrete core tests.