Effects of iron content and moisture on the microwave radiation heating and damage of sandstone

The laboratory tests of microwave radiation were conducted to study the influences of varying iron content and moisture conditions on the heating and damage of sandstone. Twelve groups of sandstone samples with varying iron content and moisture conditions( dry, natural, immersed for 24 hours, and saturated) were tested. The iron content on the sample surface was detected using X-ray fluorescence spectroscopy ( XRF ). Besides, the heating pro- cess by continuous 1. 4 kW microwave radiation was monitored by real-time infrared thermal imaging. The correlation between P-wave velocity and tensile strength was analyzed before and after radiation. The results show that the temperature rise of sandstone samples with different iron contents was slow at the early stage, active in the middle stage, and stable in the late stage under dry conditions. The peak heating rate increased with the increase of iron content, reaching 2.66, 2.40, and 1.66 TVs, respectively, and also achieving the peak earlier with 70, 100, and 110 s, respectively. Compared with iron content, the increased moisture conditions significantly affected the temperature rise of sandstone under microwave radiation. When the moisture condition was dry, natural, and immersed for 24 h, the average peak heating rates were 2.26, 3.34, and 3.24 TVs, respectively, achieving the peaks with time of 90, 70, and 20 s. However, the heating of sandstone slowed down in the saturated state, which decreased the peak heating rate to 1.3 TVs and extended peak time to 80 s. The analyses of strength and wave velocity indicate that the moisture condition significantly affected the structural damage of sandstone. However, iron content directly affected the uneven temperature distribution of the sandstone surface. The damage to sandstone after 180 s of radiation in the saturated state exceeded that after 300 s of radiation under other moisture conditions. Besides , the temperature difference of the sandstone surface was positively correlated with iron content. By comparion with dry and natural moisture conditions, the initial compaction stage of radiated sandstone subjected to 24 hour water immersion and saturation was prolonged in Brazilian splitting test. Besides, the cracking initiation mode transi-tioned from end crack initiation to center crack initiation. The research findings can provide a reference for studying microwave-assisted rock breaking in original and regenerated states. © 2024 Editorial Office of Journal of Mining and Strata Control Engineering. All rights reserved.