Influence of gas environment on the fracture healing and repair mechanism of self-healing sealing materials

Grouting sealing is the most commonly used sealing measure of extraction borehole. Under the influence of stress disturbance, the cracks sealed by grouting are easy to crack and form secondary air leakage channels. Therefore, it is proposed to develop grouting sealing materials that can make regenerated cracks self-healing. However, the underground air environment is complex, especially the crack healing performance of the hole sealing materials depends on the self-healing products generated after the exchange of materials with the air environment. Therefore, in-depth research on the influence of different gas environments on the crack healing performance of the hole sealing materials is necessary to improve the ratio of hole sealing materials. It is of great significance to realize long - term sealing of extraction borehole. In this paper, the fracture self-healing and the generation of repair products of self-healing sealing materials in vacuum, CO₂ and air environment were studied. The results showed that the hole sealing material could realize the self-healing of cracks with a width of 1.82mm in the air environment within 6 days, and the hole sealing material could realize the self-healing of cracks with a width of 1.51mm in the CO₂ environment within 8 days, while the hole sealing material could only reduce the crack width by 0.1mm in the vacuum environment within 15 days, and could not achieve complete healing. Under different environment, the material exchange law of sealing material is different from the outside world, and its mass change is quite different. In air environment, it can be divided into water loss weight loss stage, dynamic weight gain stage, secondary water loss weight loss stage and stable stage. Under CO₂ environment, it can be divided into rapid carbonization weight gain stage, slow weight gain stage and equilibrium stage. Under vacuum, the quality of the specimen is almost stable. Combined with carbonization and water evaporation, the internal law of quality change of sealing materials under different environments was analyzed. The results show that the roughness of self-healing products is the highest in air environment, the second in vacuum environment, and the least in CO₂ environment. The microscopic test results show that CO₂ does not change the main structure of the sealing material, but can only slightly increase the content of CaCO₃ in the hydration products of the sealing material, and cause the matrix porosity to decrease. However, CO₂ can significantly increase the proportion of CaCO₃ in self-healing products, and has a significant effect on promoting the particle size of self-healing products. The formation principle of self-healing products in different gas environments is quite different. The formation of self-healing products in vacuum environment lies in the precipitation caused by porous structure. In the CO₂ environment, the self-repairing products are mainly formed by carbonation, and precipitation is auxiliary. Silicate produced by secondary hydration has the largest proportion of self-repairing products in air environment, followed by carbonate produced by carbonization, and the contribution of precipitation is the least. Moderate increase of CO₂ concentration and humidity in the curing environment can promote the efficiency of self-healing of cracks. The research results are of great significance for realizing long - term sealing of extraction boreholes.