Effect of CaCO3 on hydration characteristics of C3A

Hydration products and morphology characteristics of C₃A (tricalcium aluminate)-CaCO₃-H₂O system were studied by means of XRD, DSC, FTIR spectrum analysis and SEM. The results indicate that, the new phases, i.e., C₃A·0.5CaCO₃·0.5Ca(OH)₂·11.5H₂O and C₃A·CaCO₃·11H₂O are found in this system due to the activity of CaCO₃; the formation of C₄AH₁₃ and C₂AH₈ is prohibited and the generation of C₃AH₆ is delayed in the early hydration process. C₃A·0.5CaCO₃·0.5Ca(OH)₂·11.5H₂O is not stable and will be totally transferred within 24 h; C₃A·CaCO₃·11H₂O exists stably once formation, and its flake-like crystalline phases in the early hydration transform to long rod shape, and to finally fine-needle at 28 d.