Abstract
Coal and gas outburst disasters mainly occur in geological structure belts, whose outburst coals are cataclastic, granular, or mylonitic microstructures, and their texture is loose, with mostly broken grain and pieces, so that it they hardly meet the laboratory specimen requirements. Consequently, briquettes are usually prepared at room temperature to study the mechanisms of coal and gas outburst in coal mines. In the present study, we employed a novel method of heating on briquette coal samples to investigate the effect of heating temperature on the strength and pore and fracture structure of briquette coals, and to determine the suitable heating temperature for briquette forming processes. A rock mechanics test system, MTS-815, scanning electron microscopy, nuclear magnetic resonance, and specific surface area and aperture analyzer measurements were used to analyze the mechanical parameters, morphology, and pore size distribution of briquette coal samples at different heating temperatures. The results indicate that the uniaxial compressive strength and elastic modulus of briquette coal first increased and then decreased. The pore size distribution and morphology of the briquette coal samples changed after heating. The smooth intact lamellar shape changed to a rough fractured lamellar shape, and the pores changed from unobvious micropores to observable mesopores and macropores. With an increase in the heating temperature, the transverse relaxation time spectra of the briquette coal samples decreased gradually, and both the porosity of the mesopores and macropores first increased, decreased, and then increased again. The pore diameter distributions of the five tested briquette coal samples had similar pore structures, excluding the sample heated to 600 °C. With an increase in heating temperature, pore volume, specific surface area, and average pore diameter of the briquette coal samples first decreased and then increased. The present study provides a novel method that can be applied in physical simulations aimed at preventing future disasters caused by coal and gas outburst in coal mines.
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