Chiang Mai Journal of Science

       To solve the problems of low compressive strength and unstable sealing capability of traditional hole sealing materials in the early stage of underground coal mines, a new cement-based sealing material was developed in this study by mixing ordinary Portland cement with nanomaterial, water-soluble polymer and lithium salt as additives. The early strength and the microstructure evolution of the as-prepared cement material were investigated with uniaxial compression test, scanning electron microscope (SEM), thermogravimetric analysis and X-ray diffraction (XRD). The results show that the ternary composite material (nano silicon carbide, polyvinyl alcohol and lithium sulfate) can effectively improve the early strength of cement. The 1-day compressive strength increased from 8.56 to 14.21 MPa, pointing out an improvement rate of 66.00%. It can be seen from the SEM images that a large number of fibrous C-S-H crystals and rod-shaped AFt crystals formed in the ternary composite cement sample. The nanosized silicon carbide (SiC) can accelerate the generation of hydration products through forming nucleation sites. As a dispersing agent polyvinyl alcohol (PVA) can effectively prevent the agglomeration of SiC nanoparticles and the formation of cement particle flocculation structure. On the other hand, the lithium cations and the sulfate anions of lithium sulfate could penetrate the hydration film structure and react with the hydration product Ca(OH)₂, respectively, which promotes the hydration reaction. The promotion effect of the ternary composite material on the formation of hydration products results in a clearly improved early strength of the new cement-based sealing material.