Non-destructive Surface Strength Test—Duroskop a Forgotten Tool; Comparison to Schmidt Hammer Rebound Values of Rocks

Abstract

The paper gives an overview of the test mechanism and use of Duroskop and Schmidt hammer in rock strength assessment. Duroskop is a forgotten tool that uses the same principle as a Schmidt hammer: it detects rebound values of tested surfaces. It can be applied for testing the hardness of rock surfaces to detect small scale variations in strength. Rebound values were measured on selected lithologies such as porous limestone, travertine, micro-crystalline limestone, marble, andesite tuff and basalt. The rebound values of Duroskop and 4 types of Schmidt hammer (N-34, L-9, Digi-Schmidt and PT) are compared. Not only fresh but also weathered surfaces were measured in order to assess effect of weathering on rock strength. The obtained rebound values were compared to the standardized laboratory strength test results of the same lithologies. Relationships between Duroskop rebound values and Schmidt hammer values are presented. The values of Schmidt hammer rebound and Duroskop rebound can be correlated. The latter detects minor changes in surface strength but is more sensitive to surface irregularities. Overall, these experiments indicate that special attention is needed for the interpretation of non-destructive strength test results since these tools do not provide exact data on the compressive strength or tensile strength of rocks. Nevertheless, rebound vales of Duroskop, similarly to Schmidt hammer, provide rapid information on the strength of the tested rock.