Micro-damage evolution and macro-mechanical property of preloaded sandstone subjected to high-temperature treatment based on NMR technique

Abstract

Sandstone is an important natural building material. Due to blasting, excavation disturbance and other geological disasters, the rock usually continue to work with initial damage in engineering projects. Moreover, geological high temperatures and sudden fire have a significant influence on the internal structure and mechanical stability of sandstone containing initial damage. Therefore, to study the micro-damage evolution and macro-mechanical properties of the preloaded sandstone after thermal treatment, the mechanical testing system (DSZ-1000) was used to carry out the uniaxial cyclic loading–unloading test with different stress amplitudes. Three kinds of sandstone with different initial damage were formed, and then heated at different temperatures (25 °C, 200 °C, 400 °C, 600 °C and 800 °C). Based on macroscopic mechanics and deformation analysis, the microstructure evolution of the sample was analyzed by using nuclear magnetic resonance (NMR). It is found that the preloading and high-temperature lead to mechanical properties degradation and the change of microstructure, and the energy dissipation increases with the rise in stress amplitude during cyclic loading and unloading. Meanwhile, the coupled mechanical-thermal treatment can promote significantly the development of the pore and crack of sandstone relative to the single treated method of the cyclic preloading or high-temperature. Moreover, based on the comprehensive analysis of mechanical parameters, T2 spectrum, NMR imaging, X-ray diffraction patterns and porosity, the macroscopic mechanical and microscopic damage evolution laws of the preloaded sandstone under high temperatures were determined.