Experimental study on seepage characteristics and stress sensitivity of desulfurization gypsum based concrete under triaxial stress

Converting industrial by-products into green building materials is critical to achieve a low-carbon circular economy. Permeability is an important characteristic of a material that can affect its various engineering applications. Therefore, this study investigated seepage characteristics and stress sensitivity of a green building material, i.e., modified desulfurization gypsum based concrete. Different initial load damage and dry-wet-freeze-thaw alternating cycle test groups were established by simulating the service environment. Permeability evolution of specimens under different stress states during the loading and unloading of confining pressure was obtained. The loading phase was divided into high sensitive, medium sensitive, and low sensitive areas according to the sensitive coefficient, where the corresponding permeability decreased rapidly, moderately, and slowly. The recovery degree of permeability increased gradually with the decrease in confining pressure in the unloading stage. However, the permeability value was generally lower than that in the loading stage due to the plastic deformation of pores in specimens. The higher the damage degree of initial load and the more the number of dry-wet-freeze-thaw alternating cycles, the greater the permeability loss rate of specimens. Combined with nuclear magnetic resonance results, it was found that environmental factors affect the development of pore structure of each size in specimens, resulting in different initial permeability and permeability recovery. The T2 relaxation time curve shifted to the left under confining pressure, indicating that pore size in specimens became smaller, and seepage channel became narrower, and the permeability value decreased.