Preparation of alkali-free liquid accelerator with fluorine-containing silicon residue and its accelerating mechanism

Fluorine-containing silicon residue is a solid waste that is harmful to the environment. A new Al2(SO4)3 base alkali-free liquid accelerator (LAFS) was prepared by using fluorine-containing silicon residue. The LAFS shortens the setting time and significantly improves the early strength. When the content of LAFS reaches 8.0 %, the initial setting time and final setting time of cement are 2.48 min and 11.83 min respectively, and the 1d compressive strength reaches 14.6 MPa, which is 200 % of the mortar without LAFS. In this paper, the mechanism of action of LAFS was studied by the isothermal calorimeter test, XRD, TG, SEM, and other analytical methods. The results show that the LAFS rapidly generates a large amount of ettringite in cement paste. Moreover, the LAFS promotes the formation of calcium silicate hydrate in cement paste. Finally, a conceptual model of the early hydration process of the cement paste with LAFS was established based on the analytical results.