Effect of Mineral Admixtures on the Performance of Ceramsite Shotcrete for High Geothermal Underground Engineering

[Image: see text] Ceramsite concrete is used in lining structures of underground engineering in the geothermal environment. This study, by means of mixing fly ash and silica fume, aims at diminishing the adverse effects on concrete performance caused by elevated temperature in high geothermal underground engineering. Under simulated geothermal conditions (20, 40, and 60 °C, RH ≥ 90%), it was first proposed that 15 and 5 wt % cement replacements by fly ash and silica fume, respectively, were most optimal. Then, the effect of mineral admixtures on ceramsite shotcrete performance was investigated. The results show that the mixing of fly ash and silica fume could improve ceramsite shotcrete adaptability in elevated curing temperature. Particularly for silica fume, at 40 °C curing temperature, the 28-day compressive strength and splitting tensile strength increased by 12.6 and 50.9%, respectively. The improvement effect of silica fume on permeability resistance and resistance to chloride ion permeability was higher than that of fly ash. Nevertheless, the mixing of fly ash was more effective than silica fume for reducing thermal conductivity.