Leeb hardness test to assess the mechanical properties of limestone under freeze-thaw cycles

Freeze-thaw (F-T) action can significantly weaken rock strength, posing risks to the stability of rock slopes and the durability of stone structures in cold climates. Traditional methods for assessing rock strength, such as uniaxial compressive strength (UCS) and Brazilian tensile strength (BTS) tests, have notable limitations: they can only be performed in laboratory, require numerous standardized specimens, are time-consuming, and incur high costs. In contrast, the Leeb hardness test (LHT) offers a cost-effective, non-destructive, and rapid alternative that can be conducted both in situ and in the laboratory, enabling numerous measurements on small rock surfaces. However, very limited research has investigated the applicability of the Leeb hardness index (LHD) for evaluating strength of rock materials subjected to F-T deterioration. This study aims to (1) evaluate the effects of F-T cycles on the UCS, BTS, and LHD of a Miocene limestone and (2) explore the feasibility of indirectly estimating UCS and BTS using LHD. For this purpose, limestone samples were saturated in water, exposed to 0, 10, 20, 30, and 40 F-T cycles, oven-dried at 70 °C to eliminate moisture, and mechanically tested. Each F-T cycle comprised 8 hours of freezing at -20 °C followed by 16 hours of thawing in water at 20 °C. Results revealed that after 40 F-T cycles, the UCS, BTS, and LHD of the limestone decreased by 26%, 17%, and 7%, respectively. It was also observed that the variation of strength and hardness parameters of this geomaterial can be described using a decreasing exponential decay function. Furthermore, this study provides correlation equations to accurately predict the strength properties of the limestone from its LHD, offering a valuable tool for rock mechanics practitioners.