Experimental study on the properties of cement-based materials in hot-humid and sulfate rich tunnel environments

There are frequent high-temperature geotherm disasters in the tunnels of China's western mountainous regions. The surrounding rock fissure water in the tunnels and underground water contain a great amount of corrosive salt. As a result, the lining concrete may suffer accelerated damage due to the combined attack of hot-humid environment and sulfate ions. In this context, the physical and mechanical properties of cement-based materials for shotcrete use are studied under different temperatures by simulating the interaction environment of hot-humid and sulfate, and the microscopic erosion mechanism and mesoscopic damage characteristics are analyzed. The results show that: at 20 °C and 90 °C, the relative compressive strength of cement-based materials first increases and then decreases with the increase of erosion time, but it decreases rapidly at 55 °C and loses compressive ability after 60 days; the expansion process of cement-based materials at 20 °C is divided into two stages: the "latent period" and the "significant expansion period", and the expansion velocity is greatly increased at 55 °C, while there is no significant expansion period at 90 °C; the high temperature of 55 °C will greatly increase the erosion reaction rate of sulfate, and the damage process of cement-based materials is greatly accelerated, but the high temperature of 90 °C will hinder the formation of ettringite, and significantly delay the damage of cement-based materials; different from the failure mode of layer-by-layer spalling at the end under the erosion environment of 20 °C, the specimen at 55 °C shows the failure mode of central fracture.