This study was conducted on the impact of carbonization reaction on the performance of gangue–cemented paste backfill(GCPB). Tests were conducted using a carbonization box with CO₂ concentrations of 0%,5%,and 10%. Each test was conducted for 3,7, and 28 days. We then conducted uniaxial compressive strength(UCS)testing, as well as X-ray diffraction(XRD)and scanning electron microscopy(SEM)analyses to explore the effects of the carbonization reaction on the mechanical properties of the GCPBs under the varying carbonization concentrations. The test results showed that before 28 days, the UCS of the GCPB increased with time. The higher the CO₂ concentration, the larger the contact area with the gel material;and the longer time, the slower the growth. Hydration products, such as needle-shaped ettringite(AFt)and white fibrous calcium-silicate-hydrate(C–S–H)gel, carbonize with CO₂ in the air, mainly generating CaCO₃,and combine with incompletely carbonized hydration products to act on the GCPB, increasing the UCS in its growth state. Moreover,we established a CO₂ diffusion and mass transfer equation, indicating a negative correlation between the UCS of the GCPB and the CO₂ concentration,which verified the macroscopic test results. Controlling the CO₂ concentration provides the theoretical and experimental basis for the impact of the carbonization reaction on the performance of GCPBs.

Cement paste backfill (CPB) suffers serious damage and deterioration under the dual erosion conditions of the dry–wet cycle caused by the high chloride salt concentration in mine water and the fluctuation of mine water level. In order to discuss the mechanical properties and permeability characteristics of CPB under erosion, this study designs an immersion experiment for CPB under chloride salt and dry–wet cycle conditions. Through a uniaxial compressive strength (UCS) test, the change law for the mechanical parameters of the CPB was investigated, the strength constitutive equation of the CPB was constructed and the deterioration process of the CPB was analyzed. The penetration test was used to investigate the diffusion characteristics of the packing under chloride salt and dry–wet cycle conditions. The results showed that the strength and Young’s modulus of the CPB initially increased and then rapidly decreased, with maximum decrease rates of 32.2% and 38.2%, respectively. The CPB structure exhibits an initial undamaged stage, an initial damaged stage, a damaged development stage, a damaged destruction stage and a residual damaged stage. The chloride ion penetration depth gradually increased with the number of dry–wet cycles, with a maximum diffusion depth of 20.5 mm. The maximum apparent diffusion coefficient of chloride ion was 18.99 × 10⁻¹⁰ m²/s, and the maximum concentration was 0.303 mol/L. Under the double erosion conditions of chloride salt and dry–wet cycle, the CPB structure was severely damaged.

To investigate the effect of temperature-chemical coupling on the mechanical properties of cemented paste backfill, three temperatures (20°C, 35°C, and 50°C) and sodium sulfate solution mass concentrations (3%, 5%, and 7%) are applied to simulate the complex environment in a mine. Uniaxial compressive strength and the CPB stress-strain relationship are investigated by applying stress, and the deterioration mechanism was analyzed theoretically according to physical and chemical reactions. At the same time, a structural model of the CPB deterioration mechanism under TC coupling is constructed. Combined with analysis through X-ray diffraction and scanning electron microscopy, it is shown that ettringite and gypsum are the main erosive substances that destroy the structure of CPB and that increased temperatures accelerate the chemical reaction. The concentration change consumes calcium hydroxide, changing the relationship between ettringite and gypsum. Sodium sulphate crystallization is the main form of physical deterioration. The continuous load accelerates the inelastic deformation time of CPB, resulting in a large yield deformation process.

Currently, in some domestic and foreign mines, the backfill drilling pipeline experiences a rupture phenomenon even when the wear degree is low. This results in a delay in production due to the filling becoming ‘sick’. This paper presents, for the first time, the damage mechanism from a mechanical perspective and re-derives the anti-extrusion strength model of the backfill drilling pipeline. We investigate the influence of the law on the anti-extrusion strength of pipelines from the perspective of strata and cement rings. We then verify the theoretical and simulation results through engineering examples. The results demonstrate that the Mises stress criterion is a suitable modification principle for the anti-extrusion strength model of the backfill drilling pipeline. The anti-extrusion strength of the pipeline is related to the elastic modulus and Poisson’s ratio of the stratum, and the thickness of the cement ring. It is negatively affected by the depth of the stratum. For hard strata, a cement ring with a smaller elastic modulus is suitable, while for soft stratum, a cement ring with a larger elastic modulus is recommended. When the missing angle of the cement ring is less than 60°, the stress concentration factor increases up to 2.2. The stress unloading capacity of the cement ring ranges from 32.7% to 37.8%, and optimal performance of the cement ring is achieved when it has high strength and low rigidity. The backfill filling pipeline of a copper mine abroad was destroyed due to external extrusion force exceeding its anti-extrusion strength value. The modified pipeline anti-extrusion strength model is 18.2% higher than the pipeline API strength value. This finding can inform the design of the backfill filling pipeline for China’s kilometer-deep wells in the future.

Difficulty in accurately measuring uniaxial compressive strength (UCS) under high sand-cement ratios due to press range limitations. To facilitate the computation of the UCS value of the cemented paste backfill (CPB) under the condition of high sand-cement ratio, and to analyze the size effect of the CPB with high sand-cement ratio under varied height/width ratio, the CPB specimens with sand-cement ratios of 8:1–24:1 and height/width ratio of 0.5, 1, and 2 were prepared. Through response surface experiments and finite element analysis, the influence of three height/width ratio on the CPB strength was explored, and the failure characteristics and size effect mechanisms of CPB with various height/width ratio were analyzed. The results show that the UCS of the CPB decreases with the increase of the height/width ratio under the same mass concentration and sand-cement ratio. When the height/width ratio is 0.5 and 1, the splitting failure is the main factor, when the height/width ratio is 2, the shearing failure is the main factor. The three-dimensional stress caused by the end effect of the CPB is the main reason for the high strength when the height/width ratio is 0.5. Due to the one-dimensional stress zone generated in the middle of the CPB with a height/width ratio of 2 in the laboratory, its strength value is closer to the actual UCS value of the CPB. The UCS values of the CPB with height/width ratio of 0.5 and 1 were higher than the actual UCS values in the laboratory. The rationality of the theoretical analysis was verified by the ABAQUS analysis results. This study reveals the size effect mechanism and proposes a conversion model for different specimen geometries.