# Delayed-Expansion Capsule Sealing Material for Coal Mine Overburden Isolated Grouting
## 5 Sealing Effectiveness
### Role of Fracture Aperture  
In the experimental study of sealing effectiveness across different fracture apertures, this study obtained a series of experimental results that highlight significant differences in the performance of sealing materials based on varying fracture sizes.  
As shown in Figure 17, the comparison among the leakage amount of the SAP sealing materials with the particle sizes of 20 mesh, 40 mesh, and 60 mesh at different fracture apertures reveals that a smaller particle size results in a lower leakage amount of SAP sealing materials at the early stage of the fracture, when the fracture opening is small. This is because particles with larger size in the smaller fracture openings can more easily form an effective physical barrier and are better able to interlock and form a bridge, reducing the fluid through the fracture channel, thereby better controlling the amount of leakage. With the gradual increase in the crack opening, the SAP sealing material with a particle size of 20 mesh exhibited unique advantages. A smaller particle size can penetrate the finer sections of the fracture, allowing for more effective filling and the formation of a denser sealing layer beneath larger fracture openings. This results in reduced leakage and a superior sealing effect compared to materials with a particle size of 20 mesh.  
The different particle sizes of SAP sealing materials have different advantages and disadvantages under different crack apertures. The sealing material with a particle size of 20 mesh performs better under small crack apertures, while the 60-mesh material exhibits better sealing ability under larger crack apertures. This result provides an important basis for the reasonable selection of the particle size of SAP sealing material according to the crack opening in different engineering scenarios.  
In summary, when the fracture opening did not exceed 4 mm, the sealing materials with a particle size of 20 mesh, 40 mesh, and 60 mesh, and a film ratio of 20%, were able to complete fracture sealing at a mixing ratio of 1.0%. For sealing materials with film ratios of 30% and 50%, the particle size of the sealing material must be increased, and the mixing ratio must be adjusted to 1.5-2.0% to effectively seal fractures below 4 mm. When the crack opening degree ranges from 4 to 6 mm, the mixing ratio of the sealing material with film cover ratios of 20% and 30% should not be lower than 1.5%, while the mixing ratio of the sealing material with a 50% film cover ratio should not be lower than 2.0% to achieve effective sealing. Therefore, the film cover ratio is the main influencing factor. A higher paraffin film ratio results in lower SAP content released in the sealing material after doping into water. Hence, the sealing material mixing ratio must be improved to realize  
Figure 16: Sealing effect of 60-mesh sealing material with different film cover ratios and dosages. (**a**) Dosage: 1.0%. (**b**) Dosage: 1.5–2.0%.  
crack sealing. Conversely, under the same mixing ratio, the sealing material demonstrates improved leakage control performance.