Effect of Magnesium Fluosilicate on the Properties of Sulfoaluminate Cement-Based Grouting Materials

Sulfoaluminate cement-based grouting materials (SAGMs) are frequently employed in projects concerning reinforcement and repair. Retarders are often added to SAGMs to improve their workability by delaying the hydration process. The current investigation examines the impact of magnesium fluosilicate (MgSiF6), a byproduct of phosphate fertilizer manufacturing, on the hydration and hardening process of SAGMs. The experimental results revealed that a low concentration (0.85-8.5 g/L) of MgSiF6 prolonged the setting time and decreased the compressive strength. In contrast, a high concentration (16.5-25 g/L) of MgSiF6 shortened the setting time and increased the compressive strength, but the cause of this phenomenon above is unclear. Via an examination of the impact of varying MgSiF6 concentrations on the dissolution of the primary mineral (C4A3S<overline> and CaSO4) as well as the formation process of their primary hydration products, it was discovered that low MgSiF6 concentrations inhibited the dissolution of C4A3S<overline> and CaSO4 while high MgSiF6 concentrations promoted the dissolution of C4A3S<overline> and CaSO4. The addition of MgSiF6 inhibited the formation of ettringite, and low and high MgSiF6 concentrations stimulated the formation of calcium fluoride and CaMg2Al2F12, respectively. The hydration product aluminum gel's particle size gradually decreased as the concentration of MgSiF6 increased. A low concentration of MgSiF6 generated CaF2 and hindered the formation of AFt while a high concentration of MgSiF6 promoted the dissolution and hydration of CaSO4 and C4A3S<overline> and formed nano Al(OH)3, which altered the pore structure and compressive strength.