Effect and mechanism of high Li2CO3 concentrations on the early hydration of sulfoaluminate cement-based materials

Abstract

Lithium carbonate (Li2CO3) is a commonly used early strength agent for sulfoaluminate cement based grouting materials. Low concentrations of Li2CO3 (≤30 μmol Li/g in sulfoaluminate cement) can significantly accelerate the early hydration of sulfoaluminate cement. However, the effect of high Li2CO3 concentrations (>30 μmol Li/g in sulfoaluminate cement) on the early hydration of sulfoaluminate-cement-based materials (SCBMs) is unclear. In this study, the effects of high concentrations of lithium ion (Li+) and carbonate ion (CO32) on the early hydration of SCBMs (C4A3S¯–CaSO4–CaO) with different mineral compositions (systems T1 and T2) were investigated by hydration calorimetry, X-ray diffraction, and ion concentration measurements. The results revealed that both Li+ and CO32− promoted the hydration of C4A3S¯. Li+ and CO32− each reacted with aluminum and calcium in solution, and the formation of ettringite was suppressed when they were present. At low aluminum and high calcium concentrations in solution (system T1), ettringite formation was controlled mainly by the low concentration of aluminum. Less ettringite was generated, and the inhibition of ettringite formation by both Li+ and CO32− was weaker. At high concentrations of both aluminum and calcium in solution (system T2), ettringite formed more rapidly than in system T1, and Li+ and CO32− inhibited its formation to a greater extent. Li2CO3 affected the amount of ettringite by changing aluminum ion and calcium ion in slurry, thus leading to the change of hydration heat release. These new insights into the interaction between Li2CO3 and SCBMs contribute to the theoretical foundation for cement hydration control.

Keywords

• Li+
• CO32−
• Sulfoaluminate cement
• Composition
• Hydration