Reliability of non-destructive testing methods by detecting the presence of reinforcement in existing concrete structures

Information about the reinforcement in existing concrete structures is of great importance in order to determine the moment capacity. If the rebar drawings are available, then knowledge about the rebar could be derived from the drawings. However, the rebar drawings are often not available for existing old structures or the information on the drawings could be doubted. Further investigation about the applied amount of reinforcement can be done by the use of destructive or non-destructive testing methods. Destructive investigation is often not preferred due to the required amount of labour and due to the influence on the esthetical quality of the concrete. Therefore, non-destructive methods are more preferable. Non-destructive testing (NDT) methods makes it possible to obtain information about the concrete cover depth, the number of existing reinforcement bars and the diameter of the reinforcement bars in an existing concrete structure. The ground penetrating radar and the cover meter are often used in order to obtain information about the reinforcement. Herewith the following question arise: What is the reliability of the information that has be achieved with this NDT techniques? Concrete cover depth measurements with NDT devices have a major accuracy. However, the rebar diameter measurements with NDT devices have a large spread in the measurement results and therefore a less accuracy.