Abstract
Rock destruction under high-temperature conditions is a key issue for nuclear waste treatment projects, underground coal gasification, and improvement of the use of geothermal energy for heating. Therefore, in this study, various methods and techniques were integrated to study the changes in mechanical properties, mineral composition, and microscopic fracture characteristics of Sichuan sandstone treated at 600°C. First, the fracture toughness and indirect tensile strength of untreated sandstones and high-temperature treated sandstones were tested by the MTS testing machine, and the double-K model (DKFM) was used to estimate the unstable fracture toughness. Then, the diffraction spectra of sandstone were analyzed with an X-ray diffractometer to determine the mineral composition change after heat treatment. Finally, the microscopic features of sandstone were observed through a scanning electron microscope (SEM) and optical microscope. The results show the following. (1) There is no significant change in the tensile strength and fracture toughness of Sichuan sandstone treated at 600°C. (2) The brittleness of Sichuan sandstone decreases and the ductility increases after high-temperature treatment. (3) The unstable fracture toughness value Kun obtained by the double-K model (DKFM) is significantly larger than the apparent fracture toughness value Kif. (4) After treatment at 600°C, the clay minerals in the sandstone changed significantly. Kaolinite is dehydroxylated to metakaolinite, which may increase the ductility of the rock.
Highlights
Increased demand for clean energy has promoted the rapid development of nuclear waste storage [1], geothermal energy and deep resource extraction, and underground coal gasification (UCG) [2]. e design and safety of these projects need to consider the influence of high temperatures on the physical and mechanical properties of rocks, which has aroused an interest in the study of the mechanical behavior of rock under high temperature by scholars
Talukdar et al [15] studied the effects of heat treatment on the fracture toughness (FT) of three crystalline rocks, and the results showed that, from room temperature to 600°C, the FT values of basalt, giant plagioclase basalt, and alstonite decreased by nearly 52%, 68%, and 64%, respectively. ey observed that the microcrack density increased with the increase of temperature
As the mechanical properties of sandstone after treatment at high temperature are very important in the design and safety of many important projects, a variety of methods and techniques were used to test the mechanical properties, mineralogy, and microstructure of Sichuan sandstone at room temperature and after treatment at 600°C
Summary
Increased demand for clean energy has promoted the rapid development of nuclear waste storage [1], geothermal energy and deep resource extraction, and underground coal gasification (UCG) [2]. e design and safety of these projects need to consider the influence of high temperatures on the physical and mechanical properties of rocks, which has aroused an interest in the study of the mechanical behavior of rock under high temperature by scholars. Gautam et al [3] performed tests on Dholpur sandstone and found that the uniaxial compressive strength of sandstone showed a small change within 250°C, increased from 250°C to 650°C, and began to decline after exceeding 650°C. Eir results showed that the compressive strength of granite specimens decreased with increasing temperature, while the compressive strength of sandstone did not show a significant change between room temperature and 800°C but began to decline rapidly above 800°C. Yang et al [6] tested granite in the range of room temperature to 800°C and found that the Advances in Materials Science and Engineering strength and static modulus of elasticity increased from room temperature to 300°C, peaked at 300°C, and began to decline thereafter. Sandstone is rich in clay minerals, and the changes of clay minerals during high-temperature treatment significantly affect the physical and mechanical properties of the rock; the current research into this topic is not sufficient [7]
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