Meitan xuebao (Oct 2023)
Self-healing characteristics of fracture in sealing materials based on self-healing effect
Abstract
Cement-based materials are the most commonly used grouting and sealing materials in underground coal mines, but due to the effects of stress perturbation as well as water loss and shrinkage of cementitious materials, the traditional cementitious materials are prone to regeneration cracks, which leads to the reduction of gas extraction rate in the boreholes. In order to reduce the influence of regenerated fissures on the gas extraction effect, a self-repairing cement sealing material is developed, which can realize the self-healing of fissures when the fissures are generated again at the grouting location. Firstly, the self-healing performance of self-healing cement under air conditions was studied through the fissure self-healing experiment, and a high-magnification measuring microscope was used to record the change rule of the fissure width over time. It was found that the self-healing cement was able to repair the fissure with the maximum width of 0.46 mm in 4 d under the natural air conditions. A large amount of white minerals were generated at the fissure, and the volume of repaired material still increased significantly in 14 d. After scraping off the repair products, white minerals were still generated. In order to further study the generation mechanism of the self-repair products, the microscopic morphology and microelement distribution of the two kinds of cements hydrated for 7 and 21 d were comparatively analyzed by SEM-EDS, and the physical phase information of the two kinds of cements was comparatively analyzed by XRD and Raman spectroscopy. The SEM-EDS results showed that, for the traditional cement, the needle-like and flocculent materials were cross-linked with each other and the overall structure was dense, whereas a large number of porous materials were distributed in the self-healing cement and the structure was relatively loose. Compared with the traditional cement, the mass fractions of four elements, C, Na, Al and Si, in the hydration products of the self-repairing cement were significantly higher. A large number of tightly arranged long strips are distributed on the surface of the fissure repair products, and the main elemental compositions are C, O, Na, and Ca. The XRD results showed that more diffraction peaks of unhydrated tricalcium silicate appeared in the self-healing cement compared with the traditional cement, and the hydration products of the traditional cement were mainly calcium hydroxide and calcium alumina for the same hydration time, while aluminosilicate minerals such as sodium feldspar and zeolite appeared in the self-healing cement. The fracture restorations consisted of various silicate minerals such as zeolite, calcium chalcocite and wollastonite as well as calcium carbonate, of which calcium carbonate had the highest number of diffraction peaks. The Raman spectral results showed that compared with the traditional cement, the self-healing cement had obvious Raman spectral peaks at 2860−2960 cm−1. At 7 d of hydration, the traditional cement Raman peaks were generally sharp, while the self-healing cement Raman peaks were significantly broader. More Raman peaks of high-intensity calcium hydroxide appeared in the traditional cement, while more Raman peaks of C—O vibration in \begin{document}$ {\rm{CO}}^{2-}_{3} $\end{document} appeared in the self-healing cement with larger peak area, which shows that the self-healing cement is more likely to react with CO2 in air to carbonize. At 21 d of hydration, the Raman peaks of both cements were sharp, and the main phases were hydrated calcium silicate and calcium hydroxide, while the self-healing cement also included a large amount of unhydrated tricalcium silicate. Finally, the effects of secondary hydration and carbonation on fracture self-healing were analyzed, and the equations for the generation of fracture repair products were deduced combining the experimental results.
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