Pore structure characteristics of cement stone modified by nano-MgO with different mass fractions

Effective borehole sealing plays a pivotal role in enhancing gas extraction concentration. The addition of additives to the sealing material could significantly improves borehole sealing effect. However, the impact of nanoMgO as a single additive on the sealing cement's pore structure remains unclear. Nuclear magnetic resonance and scanning electron microscopy were utilized in this study to investigate the effect of nano-MgO with different mass fractions on the cement stone's pore structure. The results indicate that when 0.5 % nano-MgO is added, the number of sealing pores of cement stone reaches the maximum, the proportion of the pore throat of the leakage pore minimizes, the cement stone's porosity is at its lowest level, and the compactness is at its highest level. Furthermore, the evolution mechanism of the pore structure of cement stone modified by nano-MgO was unmasked. The hydration product Mg(OH)2 crystal, generated by the appropriate amount of nano-MgO in the cement slurry system, gradually fills the gaps between the cement particles, reducing the formation of microcracks in the cement stone and enhancing the cement's sealing performance. However, with the addition of excessive nano-MgO, the 'sacrificial development effect' of Mg(OH)2 crystal will cause expansion pressure inside the supersaturated Mg(OH)2 crystal, which will lead to the formation of micro-cracks between crystals and between crystals and cement particles. These research findings could provide significant guidance for adding nano-MgO in sealing operations.