Prediction and Classification of Flexural Strength of Rock Materials Used as Dimension Stones

Abstract

Flexural strength is one of the important mechanical parameters of dimension stones used as flooring and surface covering. European Standards (EN) define two methods for determining flexural strength which are under concentrated load (FS3) and under constant moment (FS4). However, these test methods require precise sample preparation and specialized testing equipment. This study aims to establish correlations to practical estimation of FS3 and FS4 values from each other and also from common rock mechanics tests. For this purpose, 32 groups of building stones were tested in a comprehensive experimental study and a data set was generated. The following main findings were revealed; FS4 values are approximately 10% higher than FS3 values, Schmidt (HSL) and Leeb (HLD) hardness methods provide moderate prediction accuracy with R-2 value of similar to 0.7, uniaxial compressive strength (UCS), point load strength index (PLI), and Brazilian indirect tensile strength (BTS) tests provide higher prediction accuracy with R-2 value of similar to 0.8, especially when combined with P-wave velocity (V-P) values. In addition, anisotropy coefficients (C-A) were calculated between 3.7% and 23.1% for sample groups and it was revealed that the test parameters decreased as the C-A values increased. Based on these findings, a flexural strength classification with five categories was proposed to serve as a guideline for practical applications and projects.