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.

In order to investigate the compaction characteristics of graded crushed stone under repeated utilization, it is necessary to improve the utilization rate of road recycling crushed stone and maintain its strength and stability during recycling. In the present study, repeated compaction characteristic curves of graded crushed stone were developed using repeated compaction and screening of the graded crushed stone. The correlations between the fractal dimension of particle size distribution and repeated compaction times, water content, and dry density were analyzed. The experimental results indicate that both the maximum dry density and the optimal water content increase as the repeated compaction times increase. The fractal dimension of the particle size distribution of the graded crushed stone used in this test is 2.33 to 2.57. The obtained results show that as the fractal dimension increases, the maximum dry density of the graded crushed stone increases. At a constant repeated compaction time, the fractal dimension of the particle size distribution of graded crushed stone increased and then decreased as the water content increased. In summary, the compaction performance of the structural layer of graded crushed stone can be tuned by adjusting the fractal dimension of the particle size distribution of the recycled pavement structural layer in practical applications. Moreover, the optimal graded materials can be prepared under the guidance of the fractal dimension, thereby achieving an optimized working performance of the recycled pavement structural layer.

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.

The stress–strain characteristics of compressed sandstone are affected by many different factors. The study on the evolution law of the strain field of compressed sandstone is of great significance for disaster prediction and warning during the construction process of geotechnical engineering. In this paper, uniaxial compression tests of red sandstone of 100 mm height and 50 mm length and width were carried out under the conditions of (1) different loading rates, (2) different particle sizes and (3) different inclination angles of prefabricated fractures. Stress–strain curves corresponding to different conditions were presented, the evolution of strain field on the sample surfaces was analyzed with the help of Digital Image Correlation technology and the relationship between the stress–strain curves and the strain field was preliminarily given. This study may be helpful for obtaining a deeper understanding of the deformation and failure mechanism of sandstone under uniaxial compression.

Electrical resistivity is a sensitive indicator of rock damage, yet the quantitative link between pore-structure change and resistivity response under varied hydro-thermo-mechanical conditions remains poorly constrained. In this study, triaxial compression tests were conducted on saturated limestone at confining pressures of 5–20 MPa, pore pressures of 0–9 MPa and temperatures of 20–80 °C, with synchronous measurement of electrical resistivity and pore volume; in situ X-ray computed tomography (X-CT) was performed on miniature specimens at six characteristic loading stages to resolve the accompanying mesoscale pore-structure evolution. Resistivity tracked pore volume closely, rising to at most 1.16 times its initial value as pre-existing microcracks closed, then falling once crack propagation restored fluid connectivity, with the turning point occurring at approximately 50% of the peak deviatoric stress. A resistivity change rate per unit pore volume (ρ′) is introduced to separate the two contributions: its stage-averaged magnitude during unstable crack propagation is about 8.5 times that during linear compression, showing that crack opening alters resistivity far more efficiently than closure of an equivalent pore volume. Consistently, the cementation exponent decreased monotonically throughout loading while the electrical tortuosity reversed from increasing to decreasing at crack initiation, indicating that deformation reorganizes the topology of the conductive network rather than merely its volume. X-CT reconstruction shows pore orientation migrating progressively toward the loading axis, with 93% of the pore volume concentrated within the 18–27° interval after failure, matching the macroscopic shear angle. Crack connectivity, rather than pore fluid content, therefore governs resistivity in damaged limestone, providing a quantitative basis for resistivity-based early warning of rock mass instability in underground engineering.