Curing Pressure Impacts on Strength, Drying Deterioration and Pore Structure of Two-Component Cement–Sodium Silicate Grout

Cement–sodium silicate binary grout is widely used for water sealing and stratum reinforcement in deep underground engineering. Curing pressure profoundly affects the mechanical performance and microstructure of the hardened grout, whereas its pressure-dependent mechanical responses remain insufficiently understood. This study comprehensively investigates the grout’s workability, mechanical properties and water-loss degradation characteristics, combining scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) for microscopic analysis. The results show that the combined addition of 3% sodium bentonite and 1% polycarboxylate superplasticizer effectively mitigates slurry bleeding. An increased cement-sodium silicate volume ratio (C/S) improves fluidity and gel time, and C/S ratios of 0.4, 0.5 and 0.6 were adopted for mechanical tests. Under ambient conditions, grout compressive strength increases with curing age but declines at higher C/S ratios. Curing pressure presents a non-monotonic influence on strength: the strength reaches a minimum at 1.0 MPa and partially recovers at 2.0 MPa, which may result from the competition between pore compaction and hydration gel network damage. Water-loss-induced strength degradation undergoes three typical stages. Grout with lower C/S ratios cured under higher pressure possesses better crack resistance and residual strength. This study clarifies the pressure-adapted mechanism of the grout, providing guidance for its optimal proportioning and application in high-pressure underground engineering.