Tingting Luo

To simulate the partial immersion exposure typical of underground water storage, concrete specimens of different strength grades were partially submerged in Na₂SO₄ solution. Ultrasonic pulse velocity testing, microhardness measurements, and nanoindentation were employed to evaluate physical and micro-mechanical property degradation. In addition, the phase composition and content changes in different concrete regions using X-ray diffraction and thermogravimetric–differential scanning calorimetry are analysed to detect the time-varying phase compositions of concrete in various regions. The findings indicate that with the progress of corrosion, the overall infiltration of the wet area of C30 concrete tends to stabilize after attaining a certain height along the waterline. Subsequently, the corrosion solution gradually infiltrates and ascends along the concrete surface, leading to the overall breakdown and damage of the concrete within the climbing area from the water level line. In the corrosion and deterioration process of C40 concrete due to sulphate exposure, the corrosion solution gradually ascends from the concrete surface. The degree of surface degradation correlates with the height of the corrosion solution, eventually reaching the top of the concrete. As the sulphate surface climbing height increases, the ongoing alkali consumption reaction between the sulphate and the cement hydration product ultimately causes the fracture and decomposition of the cement stone structure.

The growth and morphological evolution of CO2 hydrates in marine sediments are recognized as highly significant for hydrate-based CO2 sequestration (HBCS). However, it remains challenging for their pore-scale processes to be directly characterized via macroscopic parameters. To ensure that issues such as weak boundaries, matrix texture interference, and internal pores in microfluidic CO2 hydrate images are addressed, an automated recognition and quantitative analysis method based on deep learning semantic segmentation was developed in this study. An image data set was compiled from microfluidic experiments, and four models (U-Net, Res-U-Net, Attention U-Net, and DeepLabv3+) were subsequently trained and compared. The results demonstrated that the hydrate regions were effectively identified by all four models. Among these, optimal performance was exhibited by the Attention U-Net model, with hydrate intersection over union (IoU) and Dice coefficients being recorded at 0.951 and 0.975, respectively. Furthermore, the optimal model was applied to continuous image sequences; consequently, the dynamic tracking of the CO2 hydrate growth process was achieved, and parameters, including hydrate saturation, internal pore ratio, and growth rate, were extracted. It was revealed that internal pores in the saline system are predominantly distributed within the hydrate envelope and that the inhibitory effect of the saline solution on hydrate growth is strengthened as the ion concentration is increased. At NaCl concentrations of 1, 3, and 5 wt %, the average growth rates were reduced by approximately 10.6%, 33.1%, and 70.4%, respectively. Among the various 3 wt % saline solutions tested, the lowest growth rate was observed in the NaCl system, whereas relatively high areal growth rates were maintained by the KCl, MgCl2, and CaCl2 systems. Thus, a reproducible pixel-level recognition and quantitative characterization approach for the microfluidic CO2 hydrate growth process is provided by our proposed method.

The consumption of concrete is enormous during coal mine construction in the Xinjie Taigemiao mining area. During the concrete production process, the cleaning of concrete tank trucks and mixer equipment generates a large amount of waste sludge separated from fresh concrete. How to successfully recycle waste sludge has become a key issue that urgently needs to be solved in mine construction. In this work, a method is proposed for reactivating waste sludge into cementitious materials by wet grinding to peel off hydration products from the surface of cement particles, and the influence of aging time and wet-grinding time on the mechanical properties and frost resistance of reactivated waste sludge paste are investigated; furthermore, through testing methods such as hydration heat analysis, XRD, and SEM, the hydration and hardening mechanisms of waste sludge treated by wet grinding are analyzed. The results show that wet grinding can break the adhesion between agglomerated waste particles and peel off the hydration products from the surface of the waste particles to obtain fresh cement particles, thereby restoring the cement’s hydration activity and bonding properties. The cementitious properties of reactivated waste sludge first increase and then decrease with the increase in aging time, and they first increase and then tend to stabilize with the increase in wet-grinding time; the frost resistance of the reactivated waste sludge is improved. The optimal aging time and optimal wet-grinding time for reactivated waste sludge are 14–18 h and 10 min, respectively.

The phase transition of paraffin powder mixed in wellbore concrete is generated by baking it, so that the paraffin powder is melted. The influence of baking temperature and paraffin dosage on phase transition degree of paraffin powder and the carbonation resistance of wellbore concrete was studied. Combined with microscopic testing methods such as scanning electron microscopy, the microscopic morphology of phase-transited paraffin films within the cement matrix and the mechanism by which they enhance the carbonation resistance of cement-based materials were analyzed. The results indicate that when baking temperature reaches 80 °C, the paraffin particles in the cement-based material can melt into viscous droplets. Partially melted paraffin particles condense within the internal pores of the cement matrix upon cooling, sealing the transmission pathways of CO₂ gas into the cement-based material. Fully melted paraffin droplets flow within the internal pores of the cement matrix and, upon condensation, firmly adhere to the pore walls, forming a relatively dense and smooth film. This film isolates CO₂ gas contact with the cement matrix, significantly improving carbonation resistance of the cement-based material. When the paraffin dosage exceeds 3% and the baking temperature surpasses 100 °C, the phase transition of paraffin powder achieves a fully carbonation-resistant effect.