Effect of Microstructure on Changes to the Pore Structure and Mechanical Properties of Limestone under Acidic Groundwater Corrosion

Rock mass subjected to acidic groundwater corrosion may cause great property alteration. In this work, the effects of microstructure on change of the pore structure and mechanical property under acid corrosion were investigated. Two types of limestone, which are microstructurally different but have almost same mineral compositions, were corroded in HCl and Na2SO4 mixed solutions with different pH values (pH = 3, 4, 5, 6, and 7). A series of approaches including uniaxial compression, Brazilian splitting, and nuclear magnetic resonance (NMR) tests were carried out to examine the strength, brittle index, porosity, and pore distribution. The mechanical properties (uniaxial compressive strength, elastic modulus, tensile strength, and brittleness index) decreased as the pH value decreased. In addition, the larger the initial microstructure, the faster the degradation rate of mechanical parameters except for the brittleness index. Moreover, NMR results revealed that the porosity increment of Group 2 (large initial microstructure) was larger than that of Group 1 (small initial microstructure). Under acid corrosion, the reason for the increasing porosity in Group 1 was the increased proportion of the internanopore, while it was transition from the supernanopore to the submicropore for Group 2. Furthermore, the brittleness index decreased as porosity increased and the proportion of the internanopore decreased. Finally, the degradation mechanisms of pore and mechanical properties were discussed.