Development of flexible organic-inorganic hybrid sprayed sealing material for small coal pillars and gob-side entry retaining

During the mining process of small coal pillars and gob-side entry retaining, cracks are prone to occur, causing air leakage in the goaf.Spraying sealing materials is the key to preventing air leakage, but existing spraying materials have problems such as poor toughness and proneness to cracking.To solve this problem, an organic-inorganic hybrid flexible sprayed sealing material was developed.The preparation principles and methods were elaborated; flowability testing, water-bleeding rate testing, toughness testing, and microstructural analysis were conducted to determine the optimal mix ratio of the new material; a leakage-sealing performance test platform capable of simulating mine pressure was constructed, and the roadway sealing effectiveness of the flexible sprayed material was validated under conditions where support wall deformation occurred due to varying pressures.The experimental results show that after organic hybridization, the inorganic cement-based materials reduce the water separation rate of the materials, and increase the fluidity and toughness of the materials.When the addition of organic lotion reaches 20%, the elongation at break increases to 8%, which is primarily attributed to the formation of a three-dimensional interpenetrating network structure within the material, thereby significantly enhancing its toughness.The optimal formulation of the new material is as follows: water-cement ratio of 0.6∶1, sodium silicate content of 2%, polyvinyl alcohol content of 3%, and VAE emulsion content of 20%.Compared with traditional cement-based materials, the internal organic network structure of flexible sprayed materials can undergo certain deformation, which enhances the leak-proofing performance by over 30%, and is less affected by mine pressure.It has a better sealing effect on air leaks such as small coal pillars and gob- side entry retaining that are prone to cracks caused by mine pressure, reducing the probability of coal spontaneous combustion.