Physicochemical characteristics and mechanism analysis of loess at different high-temperature stages

The loess overlying coal seams is subject to significant changes in its physicochemical properties due to the phenomenon of coal self-ignition, which can lead to issues such as cracking and instability of the strata. Therefore, it is crucial to investigate and analyze the physicochemical properties and the underlying mechanisms of loess subjected to heat. In this study, loess samples were heated to 200 °C, 400 °C, 600 °C, 800 °C, and 1000 °C, and a series of tests were conducted to measure resistivity, wave velocity, colorimetric parameters, acoustic emissions, porosity, and mechanical strength. The experimental results indicated that as the heating temperature increased, the tensile strength of the loess also increased. Notably, when the temperature reached 800–1000 °C, tensile strength increased from 0.36 to 0.64 MPa. The colorimetric analysis showed that the a* value exhibited a trend towards increasing redness, and magnetite formation began at 800–1000 °C, causing a shift to black and a decrease in both a* and L* values. Resistivity measurements revealed that, at low frequencies, resistivity decreased with rising temperature, while at high frequencies, resistivity increased. The wave velocity reached its lowest point at 600 °C. These findings provide a deeper understanding of the physicochemical properties and variation mechanisms of loess at different temperatures.