BS 12504-2:2021 pdf download – Testing concrete in structures Part 2: Non-destructive testing — Determination of rebound number
1 Scope This document specifies a method for determining the rebound number of an area of hardened concrete using a spring-driven hammer.
NOTE 1 The rebound number determined by this method can be used to assess the uniformity of concrete in situ, to delineate zones or areas of poor quality or deteriorated concrete in structures.
NOTE 2 The test method is not intended as an alternative for the compressive strength determination of concrete (EN 12390-3), but with suitable correlation, it can provide an estimate of in situ compressive strength. For the assessment of in situ compressive strength, see EN 13791. NOTE 3 The hammer can be used for comparative testing, referenced against a concrete with known strength or against a concrete which has been shown that it has come from a defined volume of concrete with a population verified as conforming to a particular strength class.
2 Normative references The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. EN ISO 6508-1, Metallic materials
— Rockwell hardness test
— Part 1: Test method (ISO 6508-1)
3 Terms and definitions
No terms and definitions are listed in this document. ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at
— ISO Online browsing platform: available at
4 Principle A mass propelled by a spring strikes a plunger in contact with the surface of the structure or specimen to be tested. The test result is expressed as a number in terms of the rebound distance of the mass. A number may also be obtained in terms of the energy or velocity differential before and after impact of the mass.
5 Apparatus
5.1 Rebound hammer Consisting of a spring-loaded hammer mass which, when released, strikes a plunger in contact with the surface to be tested. The rebound distance of the hammer mass from the plunger or other rebound values shall be measured.
NOTE Several types and sizes of rebound hammers are commercially available for testing various strength classes and types of concrete. Each type and size of hammer can only be used with the strength classes and types of concrete for which it is intended.
5.2 Reference anvil Steel reference anvil for verification of the hammer, with an impact area having a hardness of minimum 52 HRC when tested in accordance with EN ISO 6508-1 and a mass of (16 ± 1) kg and a diameter of approximately 150 mm.
Other anvils may be used if it can be demonstrated that the readings are within the tolerance given in 7.3.
The manufacturer’s instructions and any other equipment shall be used to ensure the longitudinal axis of the plunger is perpendicular to the surface of the anvil at impact.
Different hammers with the same rebound value on the reference anvil may not give identical results on site if the rebound value obtained lies above the normal working range of the hammer.
NOTE 1 An improved verification can be obtained by additionally using an anvil with a lower hardness that provides a second rebound value within the normal working range of the hammer (30 < R < 60 or 30 < Q < 70 where R is the rebound distance and Q is the energy or velocity measurement depending on the type of hammer used). This will ensure that different hammers obtain similar results.
NOTE 2 If the smaller anvil is used for daily verification checks on site, it is important to verify the hammer on the reference anvil at regular intervals.
5.3 Abrasive stone
A medium-grain texture silicon carbide stone or equivalent material.
6 Test location
6.1 Selection
Concrete elements to be tested shall be at least 100 mm thick and fixed within a structure. Smaller elements or specimens may be tested provided they are rigidly supported. Areas exhibiting honeycombing, scaling, rough texture, or high porosity should be avoided.
In selecting an area to be tested, the following factors should be considered:
a) the strength of the concrete;
b) type of surface (e.g. formed or unformed);
c) type of concrete (e.g. normal or lightweight);
d) moisture condition of the surface;
e) carbonation (if appropriate);
f) direction of test;
g) other appropriate factors.
A test location should be approximately 300 mm × 300 mm.