Synergistic effect of sodium metasilicate and sodium fluorosilicate in an accelerator on cement hydration

The liquid accelerator plays a vital role in shotcrete construction. Now, liquid accelerators exhibit several serious issues, including slow setting times, low late-stage strength and high preparation costs. Despite the availability of various types of liquid accelerators on the market, addressing these issues remains challenging. In this study, a low-alkali liquid accelerator (SLA) is prepared using the water bath heating method. This accelerator promotes the setting and hardening of cement and improves late-stage strength through the synergistic effect of low dosages of sodium fluorosilicate (SF) and sodium silicate (SS), while also reducing the preparation costs. At a dosage of 7% SLA, the cement paste achieves a final setting time of 3 min 30 s. The 1 day compressive strength of the mortar reaches 9.5 MPa, and the 28 day compressive strength is 7% higher than the control sample. It is found that the synergistic effect of SS and SF generates silicon dioxide gels and C–S–H gels while creating an alkaline environment that promotes the dissolution of the coating layer of hydration products and silicate mineral phases. Thus, SLA prepared through the synergistic action of SS and SF effectively overcomes the shortcomings of liquid accelerators.