Deterioration mechanism of coal gangue concrete under the coupling action of bending load and freeze–thaw

Coal gangue, as a solid waste produced in the process of coal mining, has caused great harm to the environment and society. It is the most practical means to make concrete as coarse aggregate. In practical engineering, concrete materials are often subjected to the combined action of external load and environmental factors. Simply considering the freeze–thaw effect cannot reflect the deterioration characteristics of coal gangue concrete, so that the popularization and application of coal gangue cannot be realized. Based on this, through bending load and freeze–thaw coupling test (stress level 0, 0.2, 0.4, 0.6, 0.8), the mass loss rate, relative dynamic elastic modulus, damage layer thickness, and compressive strength of coal gangue concrete with a replacement rate of 40% were analyzed. The degradation characteristics of pore structure and interface transition zone of coal gangue concrete were studied by nuclear magnetic resonance test and microhardness test. The effects of different stress levels on pore size distribution, pore grade ratio, pore fluid characteristics, and interface zone characteristics were analyzed. The results show that the larger the bending stress ratio is, the faster the degradation of compressive strength and relative dynamic elastic modulus of coal gangue concrete is, the faster the thickness of damage layer increases, the larger the proportion of large pores in the specimen is, and the pore connectivity is enhanced. In addition, the interface area between coal gangue aggregate and mortar is the weak position of coal gangue concrete, and its thickness and microhardness are widened and decreased with the increase of stress level. The deterioration of the interface area makes the specimen close to failure.