Correlation and correction factor between direct and indirect methods for the ultrasonic measurement of stone samples

This study focused on analyzing and calculating the correction factor between direct and indirect methods for the ultrasonic testing of stone monuments using a customized transducer and couplant. To achieve this goal, the P-wave velocity in 11 rock specimens, including two artificially weathered samples, was measured in a laboratory by applying both direct and indirect methods using an ultrasonic tester. Statistical interpretation of the results revealed that the indirect P-wave velocities were always lower than the direct velocities, with the correction factors between them differing by rock type. The average correction factors produced by the indirect method were 1.50 in the medium-to coarse-grained granite sample, 1.37 in fine-grained granite, 1.58 in fine-grained diorite, 1.38 in medium-grained diorite, 1.59 in sandstone, and 1.71 in marble. In addition, the regression equation and coefficient of determination, R-2 were acceptably high, suggesting a sufficient relationship between the two variables for use in engineering. This study will significantly contribute to improving the reliability of ultrasonic testing for weathering evaluation of a stone monument.