The methods based on the rebound principle consist of measuring the rebound of a spring driven hammer mass after its impact with concrete. The test has been widely used, since its introduction in 1948. The main reason behind its popularity, is its simplicity, and convenient of use for field applications. Rebound hammer is used to evaluate the surface hardness. Exist empirical correlations have been established between strength properties and the rebound number. The test method has been standardized. To use this test method to estimate strength, it is necessary to establish a relationship between strength and rebound number for a given concrete and given apparatus. Such relationship can be established by correlating rebound numbers measured on the structure with the measured strengths of cores taken from corresponding locations. It is easy to use for most field applications and the test can be used to study the uniformity of concrete. Disadvantages: The method is very subjective and surface condition, presence of rebar, presence of sub-surface voids can affect the test results.
Design codes: UNI EN 12504-2