Phase evolution of fly ash calcium constituent at early alkali activation reaction age

• Time-resolved calcic phases were well detected by XRD, SEM, and TEM.
• Calcic phase evolution processes of CFA during AAR were initially proposed.
• Be of great significance for the synthesis control of AAFAMs.

Calcic phases are well documented to be the key-strength-giving components of alkali activated materials (AAMs). The clearness of phase evolution processes of fly ash calcium constituent during alkali activation reaction (AAR) will be of great significance to both the cognition and synthesis control of AAMs from fly ash. By tactfully combined the AAR kinetics study with XRD, SEM, and TEM-EDX investigations, different calcic phases at different AAR periods were well detected in this study, which has given important indicative information for the clearness of calcium phase evolution. Based on that, a reasonable mechanism in terms of fly ash calcic phase evolution process was proposed in this paper.