Leeb hardness for yielding stress assessment of steel bars in existing reinforced structures

The assessment of the mechanical properties of steel bars in existing reinforced concrete is crucial as much as the estimate of concrete strength. Till now no Non Destructive Tests (NDT) or Moderately Destructive Tests (MDT) have been developed to this aim. In this paper the Leeb durometer is applied to reinforced concrete (r.c.) steel bars either extracted from the structures, to be tested in laboratory, and directly tested in situ. The surface is smoothed by means of a procedure that guarantees very low roughness (1.6 mm), less than the value required by the Leeb method (10 mm). A correlation between Leeb hardness and yield strength is provided and validated by comparison with other well established equations in literature and test data. Even though the large variety of steel types, mainly of the early 20th century, makes the data fitting not fully satisfactory, the procedure may be extensively used as a MDT technique to investigate the properties of steel bars in addition to direct tensile tests on samples extracted from the structure.