Abstract: FBC ash contains much calcined clay minerals, sufficient free lime and anhydrite, so ettringite can be found in cemented FBC ash paste. To describe the stability of ettringite in FBC ash paste, the content change of it by the age was studied by X-ray diffraction (XRD) and chemical analysis. The results show that the content of ettringite increases with ages before 28 d cured in standard condition, but decreases subsequently. It is affirmed that the stability of ettringite in FBC ash paste is poor, and the formed earlier will decompose.

Key words: FBC ash%hydration%ettringite%stability