Abstract:The permeability of basalt fiber reinforced concrete is critical to the durability assessment of members after fire, and considering the load effect can better reflect the actual members status. For this purpose, the permeability of basalt fiber reinforced concrete after high temperature is tested under variable confining stress, and the change characteristics of pore structure before and after confining stress are studied. The results show that the permeability decreases with a negative exponential function under variable confining pressure. Compared with non-added fiber, the initial permeability of basalt fiber specimens after the temperature of 100 ℃, 300 ℃, and 600 ℃ is 48.16%, 33.89%, 1.57%. The permeability changes at each stage of confining pressure loading is evaluated by confining pressure sensitivity coefficient and dimensionless permeability, which is divided into sensitive zone, transition zone and insensitive zone. The original pore structure of specimen is adjusted after confining pressure, which is reflected in the development to small-size pores, the proportion of micro-pore is more than 90%, and the number of pores decreases, thus reducing the permeability.