Coupled acid–salt erosion mechanism of solid waste–based grouting materials for submarine tunnels

The traditional cement-sodium silicate (C-S) double-liquid grouting materials have been widely used in submarine tunnel engineering applications. However, their mechanical strength and long-term durability could still be further improved to better meet the demands of challenging engineering environments. To improve the performance of C-S materials, this study developed a solid waste-based grouting material (SWGM) incorporating silica fume and waste glass powder, and systematically examined its deterioration mechanisms under coupled acid (sulfuric/citric acid) and marine salt corrosion. Coupled acid-salt erosion mechanism and material optimization were investigated through appearance morphology, neutralization depth, mass variation, strength development, and microstructure. SWGM exhibited enhanced durability compared with C-S materials, showing reduced mass loss and improved mechanical performance under salt and acid exposure. Under salt attack, mass variation decreased by 0.86%, with flexural and compressive strengths increasing by 2.50 and 2.10 MPa, respectively, while citric acid erosion led to lower strength loss (2.49% flexural, 16.97% compressive). In sulfuric acid, 56-day flexural and compressive strengths increased by 0.38 and 0.67 MPa. These improvements were attributed to inhibited formation of Friedel’s salt and ettringite, enhanced pozzolanic reactions, and a denser, chemically stable matrix, whereas sulfuric and citric acids induced damage mainly via ettringite/gypsum formation and C-S-H decalcification.