Rebound hammers, commonly referred to as Schmidt Hammers, are used to ascertain approximation of the uniaxial strength of rock or most typically the compressive strength of concrete by testing the surface hardness of the material. Schmidt hammer tests are effective for instantaneous results in the field giving an approximation of the surface hardness for correlation with approximate compressive strength of the material.

However, there are several factors which can affect the reliability of readings such as the presence of surface contaminants, poor finishes, presence/locations of aggregates, carbonation etc, which all effect the surface hardness. Therefore, it is recommended that Schmidt hammer testing is not undertaken in isolation and is correlated with core compressive strength results.  Empirical offer trained engineers to undertake tests in accordance with BS EN 13791 Assessment of in-situ compressive strength in structures and precast concrete components, and BS EN 12504 Non-destructive testing – Determination of rebound hammer.

Rebound hammer testing should be used as means of assessing variations of strength for particular elements rather than an accurate means of measuring the strength, it is one of the oldest methods for comparing concrete in different parts of structure and can be used as a means of assessing strength gain over an element/structure during construction projects.