Synergistic effect of Na2SiO3 and Na2SiF6 in an accelerator on cement hydration

The liquid accelerator plays a vital role in the shotcrete construction. Now, liquid accelerators exhibit several serious issues, including slowly setting times, low late-stage strength, and high preparation costs et al. Despite the availability of various types of liquid accelerators on the market, addressing these issues simultaneously remains challenging. 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 fluosilicate (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 d compressive strength of the mortar reaches 9.5 MPa, and the 28 d compressive strength is 7 % higher than the control sample. It is found that the synergistic effect of SS and SF generates SiO 2 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, the SLA prepared through the synergistic action of SS and SF effectively overcome the shortcomings of the liquid accelerators.