Effect of metal chelating agents on crack self-healing and mechanical properties of cement-based sealing materials

Grouting sealing quality is recognized as a critical factor ensuring gas drainage efficiency. Influenced by mining stress disturbance and slurry dehydration shrinkage, sealing materials tend to crack and form secondary fractures, leading to gas leakage in drainage boreholes. To address this issue, a self-healing grouting sealing concept is proposed where sealing materials spontaneously react with environmental moisture and CO₂ through self-healing agents to generate CaCO₃ precipitation for crack closure when gas leakage occurs. However, the self-healing agent interferes with the hydration reaction of sealing materials and negatively impacts mechanical properties. Building on existing research, the content of self-healing agent is adjusted to balance self-healing capacity and mechanical performance. Results indicate that reduced self-healing agent content decreases crack-repairing capability. Specimen S1 achieves a maximum repairable crack width of 0.88 mm after 4 days of curing, while S2 and S3 specimens require 5 days to repair maximum crack widths of 0.73 mm and 0.71 mm, respectively. Meanwhile, mechanical properties improve significantly, with compressive strength increasing from 3.23 MPa (S1) to 4.31 MPa (S2) and 8.85 MPa (S3). To investigate self-healing agents' effects on pore-sealing materials, microstructural and mineralogical analyses revealed that reduced agent dosage enhanced hydration product formation and densification, forming a continuous network, while XRD indicated a mineralogical shift toward diminished unhydrated clinker (3CaO·SiO₂, 2CaO·SiO₂) peaks and intensified hydration product (C-S-H gel, Ca(OH)₂) peaks. By optimizing the self-healing agent content, it is found that a 12% dosage achieves balanced self-repair capability and significantly improved mechanical performance. These findings hold substantial significance for regulating the self-healing properties and mechanical performance of sealing materials.