This study utilized X-ray computed tomography (CT) technology to analyze the meso-structure of concrete at different replacement rates, using a coal gangue coarse aggregate, after experiencing various freeze–thaw cycles (F-Ts). A predictive model for the degradation of the elastic modulus of Coal Gangue coarse aggregate Concrete (CGC), based on mesoscopic damage, was established to provide an interpretation of the macroscopic mechanical behavior of CGC after F-Ts damage at a mesoscopic scale. It was found that after F-Ts, the compressive strength of concrete, with coal gangue replacement rates of 30%, 60%, and 100%, respectively, decreased by 33.76%, 34.89%, and 42.05% compared with unfrozen specimens. The results indicate that an increase in the coal gangue replacement rate exacerbates the degradation of concrete performance during the F-Ts process. Furthermore, the established predictive formula for elastic modulus degradation closely matches the experimental data, offering a reliable theoretical basis for the durability design of CGC in F-Ts environments.

To study the deformation characteristics of crushed gangue under different water content conditions, the confined compaction test of crushed gangue was carried out under five different water content conditions by using a universal material testing machine and a compaction device. The strain–stress relationship in the compaction process of crushed gangue and the crushing law of gangue particles were obtained through the test, and the effects of the axial stress, water content, and relative crushing rate on the compaction deformation of crushed gangue were analyzed. The results show that the confined compaction deformation process of crushed gangue can be divided into three stages: the rapid compaction stage, crushing compaction stage, and stable compaction stage. The strain–stress relationship can be described by the parameter logarithmic function and Chapman–Richards function, respectively. The maximum change in the compression modulus under different water content states ranged from 9.9 to 19.3 MPa, and the influence of the water content on the compression modulus was more significant with increasing axial stress. There is a good correlation between particle crushing and compaction deformation. The relative crushing rate increases with the increase in the axial strain, and the increasing rate of the relative crushing rate also gradually increases. The change law of the relative crushing rate and axial strain is different in dry and water-containing conditions.

Incomplete data indicate that coal gangue is accumulated in China, with over 2000 gangue hills covering an area exceeding 200,000 mu and an annual growth rate surpassing 800 million tons. This accumulation not only signifies a substantial waste of resources but also poses a significant danger to the environment. Utilizing coal gangue as an aggregate in the production of coal-gangue concrete offers an effective avenue for coal-gangue recycling. However, compared with ordinary concrete, the strength and ductility of coal-gangue concrete require enhancement. Due to coal-gangue concrete having higher brittleness and lower deformation resistance than ordinary concrete, basalt fibre (BF) is a green, high-performance fibre that exhibits excellent bonding properties with cement-based materials, and polypropylene fibre (PF) is a flexible fibre with high deformability; thus, we determine if adding BF and PF to coal-gangue concrete can enhance its ductility and strength. In this paper, the stress–strain curve trends of different hybrid basalt–polypropylene fibre-reinforced coal-gangue concrete (HBPRGC) specimens under uniaxial compression are studied when the matrix strengths are C20 and C30. The effects of BF and PF on the mechanical and energy conversion behaviours of coal-gangue concrete are analysed. The results show that the ductile deformation of coal-gangue concrete can be markedly enhanced at a 0.1% hybrid-fibre volume content; HBPRGC-20-0.1 and HBPRGC-30-0.1 have elevations of 53.66% and 51.45% in total strain energy and 54.11% and 50% in dissipative energy, respectively. And HBPRGC-20-0.2 and HBPRGC-30-0.2 have elevations of 31.95% and 30.32% in total strain energy and −3.46% and 28.71% in dissipative energy, respectively. With hybrid-fibre volume content increased, the elastic modulus, the total strain energy, and the dissipative energy all show a downward trend. Therefore, 0.1% seems to be the optimum hybrid-fibre volume content for well-enhancing the ductility and strength of coal-gangue concrete. Finally, the damage evolution and deformation trends of coal-gangue concrete doped with fibre under uniaxial action are studied theoretically, and the constitutive model and damage evolution equation of HBPRGC are established based on Weibull theory The model and the equation are in good agreement with the experimental results.

To study the energy dissipation characteristics and damage evolution law of sandstone under cyclic loading, uniaxial cyclic loading tests are conducted on sandstone specimens under different frequencies with an MTS‐815 rock testing machine. Furthermore, the characteristics of elastic modulus and energy evolution law during cyclic loading and unloading are explored. The results show that the loading and unloading moduli increase with the loading frequency. Under higher frequencies, the deformation resistance of the specimen is stronger, the elastic energy stored in a single cycle of loading is larger, the released energy is less, and it is less likely for the specimen to be damaged. At the beginning of loading, the energy dissipation ratio K decreases slowly with increasing loading cycles, and it then remains stable. When the specimen is close to failure, an inflection point of K appears, and K increases rapidly. Furthermore, the evolution equation of the damage variable is derived according to the strength characteristics and energy evolution law in the process of cyclic loading, and the reasons for the failure of sandstone specimens are explained from the perspectives of energy and fatigue damage.

The mechanical response characteristics of sandstone specimens under different stress amplitudes and loading frequencies were tested by a TAW-2000 rock triaxial testing machine. The characteristics of the stress-strain curve and the evolution process of strain damage under cyclic loading are analyzed. Based on creep theory and the disturbance state concept, a theoretical model between the axial compressive strain, axial compressive stress, and cycle number is established. The results show that there exists an upper threshold value of stress in cyclic loading above which the specimen will be damaged. As peak stress increases, the energy loss and irreversible deformation caused by damage gradually increase. When loading to an unstable peak stress under cyclic loading, the fatigue damage of sandstone under cyclic loading undergoes three characteristic stages: the initial stage; the stable stage; and the accelerated failure stage. The parameters of the strain damage model based on the disturbance state concept of sandstone are identified by test data, and the rationality of the model is validated by comparing theoretical values with experimental measurements.