# Delayed-Expansion Capsule Sealing Material for Coal Mine Overburden Isolated Grouting
## 5 Sealing Effectiveness
### Role of SAP Materials  
The sealing effect under different fracture openings, different coating ratios, different sealing material dosing ratios and other parameters is shown in Figure 13.  
Considering the fracture opening of 2 mm as an example, sealing materials with a particle size of 20 mesh, 40 mesh, and 60 mesh and overlay ratios of 20%, 30%, and 50%, respectively, were used for sealing. The mixing ratios of these three types of sealing materials were 1.0%, 1.5%, and 2.0%. Initially, the 20-mesh sealing material with a mixing ratio of 1.0% was applied to seal the 2 mm fracture. The experimental results shown in Figure 14 indicate that only the sealing material with a particle size of 20 mesh and overlay ratio of 20% achieved fracture sealing, with complete sealing achieved within 20 min. The leakage amount at the outlet was 0 g/min at 0-3 min. Subsequently, the leakage amount at the outlet increased from 0 g/min to 199 g/min at 3-4 min. Then, the leakage amount decreased continuously, ultimately reaching 169 g/min at 10 min. Then, the leakage amount started to decrease abruptly until the leakage amount at the outlet was 0 g/min at 20 min to complete fracture sealing. For the 20-mesh sealing material with the film cover ratios of 30% and 50%, significant leakage persisted at the exit during the grouting process, preventing complete fracture sealing. However, when the mixing ratio of the 20-mesh material with a film cover ratio of 30% was increased from 1.0% to 1.5%, effective sealing of the slurry fracture was achieved within 14 min. The sealing material with a particle size of 20 mesh and film cover ratio of 50% required an increase in the mixing ratio from 1.0% to 1.5%, but still failed to fully seal the slurry leakage fracture. However, when the mixing ratio was increased to 2.0%, effective sealing of the fracture was achieved within 15 min. Figure 13: Sealing renderings under different conditions. The results (Figure 15) obtained by experiments using a sealing material with a particle size of 40 mesh and film cover ratios of 20%, 30%, and 50% on a 2 mm fracture reveal that the 40-mesh material with 20% film cover achieved complete fracture sealing at the mixing ratio of 1.0% within 14 min. However, for the 40-mesh materials with 30% and 50% film cover, significant leakage persisted throughout the grouting process, preventing effective fracture sealing. During the grouting process, substantial leakage occurred, preventing successful fracture sealing. When the sealing material with a particle size of 40 mesh and film cover ratio of 30% was used at the mixing ratio of 1.0%-1.5%, effective fracture sealing was achieved within a sealing time of 17 min. The sealing material with a particle size of 40 mesh and film cover ratio of 50% did not achieve effective fracture sealing at the mixing ratios of 1.0%-1.5%. However, increasing the mixing ratio to 2.0% resulted in successful slurry fracture sealing, with a sealing time of 17 min. The experimental results for sealing a 2 mm fracture using sealing material with a particle size of 60 mesh and film cover ratios of 20%, 30%, and 50% are shown in Figure 16.  
The sealing materials with a particle size of 60 mesh and film cover ratios of 20% and 30% achieved successful fracture sealing at the mixing ratio of 1.0%, with sealing times of 11 min and 14 min, respectively. However, the sealing material with a particle size of 60 mesh and film cover ratio of 50% consistently exhibited significant leakage at the outlet during the grouting process, resulting in failure to complete fracture sealing. However, by  
Figure 14: Sealing effect of 20-mesh sealing material with different film cover ratios and dosages. (**a**) Dosage 1.0%. (**b**) Dosage 1.5–2.0%. Figure 15: Sealing effect of 40-mesh sealing material with different film cover ratios and dosages. (**a**) Dosage: 1.0%. (**b**) Dosage: 1.5–2.0%.