Effect of the Size Factor on Leeb Hardness Performance in Pyroclastic Rocks

Abstract

The aim of the study is to research the effect of sample size on the Leeb hardness (HL) test, commonly used as an indirect, non-destructive, cost-effective and practical method to predict the uniaxial compressive strength of rocks. Within this scope, cube samples were prepared with 3, 4, 5, 6, 7, 8, 9 and 10 cm edges from 10 different pyroclastic rocks with physical features (density, porosity, P-wave velocity) varying over a broad interval. After identifying the physical (dry density, porosity and P-wave velocity), mineralogical and textural features of each sample, the HL test was applied under laboratory conditions to investigate the effect of the size factor. Correlation analysis between HL values and sample size revealed that samples with cube edge lengths below 8 cm exhibited markedly lower HL values, accompanied by substantially higher standard deviations. An 8 cm cube edge length was identified as the minimum reliable sample edge length for HL measurements of pyroclastic rocks. HL testing is not recommended for rocks containing components with contrasting surface hardness values. The findings are expected to contribute to the application of Leeb hardness, with expanding areas of use in recent years, in more effective and reliable ways in engineering projects.