Improving Mechanical Performance and Frost-Thermal Durability of Basalt Fiber Shotcrete in Extreme High-and-Low Temperature Environments

The mechanical properties of basalt fiber (BF) shotcrete at high-frigid condition and high temperature environment are comprehensively studied. The test specimens are prepared at different ambient temperatures, fiber contents and curing time, and the cubic compressive strength, splitting tensile strength and flexural strength parameters are analyzed to figure out effects of BF. The frost resistance and thermal conductivity of BF shotcrete are further studied and evaluated, and compared with steel fiber (SF) and BF with different fiber lengths. The results showed that: (1) The addition of BF can significantly improve the compressive strength of shotcrete in the high-frigid condition and high temperature, and the more extreme the environment is, the more obvious the improvement is. (2) The addition of BF can greatly improve the splitting tensile strength of shotcrete in high-frigid condition. In the high temperature environment, whether it is 7d or 14d, its strength value is higher than that of shotcrete, and the peak of strength is reached at 40 ℃. (3) The BF can obviously improve the flexural strength in high-frigid condition, and its flexural strength is far superior to that of shotcrete without BF. In the later stage of curing, BF has a great improvement in the strength of shotcrete. (4) After 100 freeze-thaw cycles, the compressive strength, splitting tensile strength and relative dynamic elastic modulus of shotcrete decrease in different proportions. The strength of BF with a fiber length of 16 mm (BF16) is the highest, and the performance of plain concrete (PC) is the worst. Relatively speaking, the performances of PC and BF50 shotcrete are extremely poor, and the strength loss rate after freeze-thaw cycles is large. SF can relatively improve the decrease of the dynamic elastic modulus of shotcrete, but the effect is not as good as BF, of which BF16 has the most significant effect. (5) The addition of BF can effectively reduce the thermal conductivity of concrete, especially when the length of fiber is 16 mm, the reduction is the largest, that is, the concrete has better resistance to heat.