Effect of Composite Fibers and Nanosilica on the Properties of Cement-Based Sealing Materials.

Sealing materials play an important role in the safety of coal mine production. To improve the efficiency of coal mine gas mining, it is necessary to optimize the performance of the sealing materials. In order to develop new sealing materials with better performance, it is necessary to improve the formula of the cement materials. In this study, poly(vinyl alcohol) fiber (PVAF), polypropylene fiber (PPF), nanosilica (NS), and their composite materials were added to the composite cement-based materials of Portland cement and sulphoaluminate cement, respectively, and a new cement-based hole sealing material was prepared. The effects of these additives on fluidity, setting time, and compressive strength of cement-based sealing materials were studied through experiments. X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, and pore size analysis were used to study the influence of composite fiber and nanosilica on the properties of the cement system. The results show that PVAF, PPF, and NS all effectively improve the mechanical properties and stability of the cement system, in which PPF: PVAF = 3:1 and the content of nanosilica ranges from 0% to 3%, and the performance of the cement system can be improved. When the content of NS is 3%, PPF is 0.05%, and PVAF is 0.15%, the compressive strength at 28 days reaches 30.5 MPa. The addition of NS can make the hydration degree of cement materials higher, and PVAF and PPF can improve the distribution of hydration products, reduce the generation of harmful pores with pore size greater than 10 nm in the cement pore system, and significantly improve the properties of materials. This effectively maintains the stability of the borehole in the process of gas drainage, improves the gas drainage concentration of the borehole, and enhances the gas drainage effect.