Experimental study of strength, pore structure and phase evolution characteristics of iron tailings cemented paste backfill under high-temperature

Abstract

With the deepening of mining depth, the geothermal temperature faced by the pit backfill is getting higher and higher, so the spontaneous combustion probability of sulfur-bearing minerals increases. In addition, sudden fires can expose the backfill to high temperatures, which will endanger the structural safety of the backfill. Therefore, in order to fully understand the mechanical response and pore structure evolution characteristics of backfills under high-temperature loading, the compressive strength and splitting tensile strength of backfills with different ages: 7 days, 28 days and 60 days and cement-tailings ratios: 1:6, 1:8 and 1:10 were tested using high-temperature furnace to simulate different temperature loads: 100, 200, 400, 600 and 800°C. The pore structure characteristics of the backfill after high temperature are analyzed by mercury intrusion porosimetry. To further understand the mechanism of backfill transformation at high temperature, the phase evolution characteristics of iron tailings and cementitious materials are analyzed by X-ray diffractometer and differential ther-mal/thermogravimetric analyzer. The results show that the strength and pore structure of iron tailings backfi ll at high temperature are related to the curing age. The strength and most probable pore size of backfill cured at 7 days increased fi rst and then decreased with the increase of temperature. Among them, the compressive strength and splitting tensile strength reached their peak values at 200°C and 100°C, respectively. While after 28 days, the pore size increased with the increase of high temperature, and the strength of backfill decreased continuously with increasing temperature. No matter what age of backfill is, it almost loses its tensile strength after being subjected to a high temperature above 400°C. These characteristics are closely related to the expansion of mica in iron tailings and the dehydration and decomposition of cementing material hydration products, such as ettringite and C-S-H phase at high temperature.