Pore structure, mechanical property and permeability of concrete under sulfate attack exposed to freeze-thaw cycles

This study experimentally investigated the variations in pore structure, mechanical property and permeability of concrete under sulfate attack exposed to freeze-thaw cycles, and examined the relationship between pore structure, stress, and permeability. The results indicate that before 10 cycles, the original pores in the specimen are filled with the reaction products of sulfate and concrete matrix. Compared with the specimen at 0 cycles, it is denser with a reduction in T2 area, an increase in peak stress, and a decrease in initial permeability. With the increase in the number of cycles, the accumulation and expansion of ettringite and gypsum in the product lead to the subsequent enlargement of pores, more liquid enters the interior of the specimen, and the frost heave effect caused by the freeze-thaw dominates. Therefore, the mesopores and macropores in the specimen are developed, the fractal dimension is reduced, and the T2 area is increased. Macroscopically, the peak stress decreases and the initial permeability increases. Besides, the existence of hydraulic pressure weakens the mechanical properties (peak stress and deformation modulus) of the specimen, increases the lateral deformation and improves the permeability.