Quantitative Analysis on Tensile Mechanical Properties and Microscopic Characteristics of Acidified Limestone

The hard rock roof in coal mines is prone to failure, causing catastrophic disasters due to highly concentrated stresses. Acidification can effectively degrade the resulting mechanical properties of hard rocks. Therefore, quantitative assessment and understanding of the tensile properties and microscopic characteristics of acidified limestone is essential for rock engineering. In this work, Brazilian splitting tests (BSTs) were carried out on acid-immersed limestone specimens and the resulting properties were determined by digital image correlation (DIC), 3D scanning, and nanoindentation. The effects of varying pH values on tensile properties, splitting surface morphology, and nanoindentation characteristics were investigated. The results indicate the tensile strength decreases with the decrease in pH value, while the splitting failure mode gradually transitions from I-shaped tensile to Y-shaped tensile-shear failure mode. Further, DIC results indicate that the maximum principal strain increases gradually. The evaluation of the splitting surface also showed that the roughness, relative fluctuation height, angle, area ratio of the splitting surface, and the range of indentation depth increase as the pH value decreases, while the relative fluctuation height increases the most. Nanoindentation confirms that the micromechanical parameters (hardness, modulus, and fracture toughness) degrade to varying degrees due to the acidification. Finally, the correlation between tensile strength and micromechanical parameters was developed for a better understanding of the microscopic deterioration mechanism in acidified limestone.