The structure under consideration is divided into groups (test regions) of elements having been casted together.

For assessment of in-situ compressive strength for statistical and safety reasons, as many cores as are practicable should be used. An assessment of in-situ compressive strength for a particular test region shall be based on at least 6 cores. This should be enough in order to classify the in-situ compressive strength according to the relative concrete classes (i.e. C20/25, B225 etc).