In this study, an investigation was carried out to elucidate if the core holder type affects the measured Leeb hardness values (HL) of rock materials obtained by using the Equotip hardness tester. To achieve this goal, NX-size core specimens of different rock samples were subjected to Leeb hardness testing by employing an ‘Arch-shaped’ and a ‘V-shaped’ core holder. The results indicated a strong degree of linear correlation (R2 0.95) between mean rebound hardness values determined in the arch-shaped holder (HLA) and V-shaped holder (HLV). The maximum difference in HL values obtained from the two holders was 74.2 units on the HL-scale, corresponding to a difference of 10.2 %. Although the differences in magnitudes of HLA and HLV values were small and varied from one rock variety to another, there was a tendency of the V-shaped holder to give relatively lower values. On the other hand, when compared to the minimum values, a higher statistical correspondence was observed between maximum HLA and HLV values. The results also showed that it is possible to predict uniaxial compressive strength of the tested rocks reliably by employing any of the holders.
Core holder, Equotip hardness tester; Leeb hardness; Uniaxial compressive strength; Rebound hardness