Abstract
Microwave-induced rock fracture is one of the promising approaches of achieving non-blasting continuous mining and assisted mechanical rock breaking. It is of great theoretical and practical significance to study the temperature effect and fracture characteristics of rocks of different sizes under microwave heating; however, there are few studies in this field. Microwave heating of φ 50 × 100 mm, φ 50 × 50 mm, and φ 50 × 25 mm sandstone samples with different heating powers and times was performed to measure the temperature of the sample, the microwave energy absorbed, the mass, and the P-wave velocity before and after heating. The results show suppress that (i) under the same heating conditions, the mass difference and the temperature increase range of φ 50 × 100 mm and φ 50 × 50 mm samples are larger than that of the φ 50 × 25 mm samples; (ii) the wave velocity change rate and the damage factor of samples increase with the increase of heating power and time; (iii) different size specimens have different crack- propagation modes. The main crack of φ 50 × 100 mm specimens usually starts from the middle of the height of the specimen; for the φ 50 × 50 mm specimens, it usually starts from the middle or bottom-end surface of the specimen height; the main crack of φ 50 × 25 mm specimens starts from the vertical surface of the specimen. With an increase in the heating time, the length and width of the main crack continuously increase and secondary cracks are generated. The fracture mode of the sample is also related to the size of the sample. The fracture mode can be divided into three parts: melt fracture, thermal-expansion fracture, and secondary thermal-expansion fracture. The relationship between the sample temperature and the absorbed microwave energy is approximately linear.
Highlights
The mechanized continuous mining of hard rock in mines of metal ores is a future mining trend and has been applied in some local hard rock areas of mines
50 mm specimens, it usually starts from the middle or bottom-end surface of the specimen height; the main crack of φ 50 × 25 mm specimens starts from the vertical surface of the specimen
Under different heating powers and microwave heatingthan is smaller than mass ofbefore the sample before heating
Summary
The mechanized continuous mining of hard rock in mines of metal ores is a future mining trend and has been applied in some local hard rock areas of mines. Wang et al [10] studied the effect of microwave heating on the porosity, permeability, structure, and pore-size distribution of tight sandstone. He et al [11] studied the thermal damage effect of diorite (25 × 25 × 25 mm) under microwave heating; the sample was heated to 500 ◦ C and began to break, and at 700 ◦ C completely disintegrated, and the possible causes of diorite thermally affected fractures were discussed. Microwave heating tests were performed on sandstone samples of different sizes by using a special microwave rock breaking system, and the temperature effects, crack propagation, and fracture characteristics of different size samples were obtained. The heating power was monitored in real time to calculate the absorbed microwave energy and obtain the relationship between temperature and energy of different sizes
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