Hydration reaction and hardening of calcined clays and related minerals.: II. Influence of mineralogical properties of the raw-kaolinite on the reactivity of metakaolinite

Hydrates which form during the setting of calcium hydroxide-activated metakaolinite cements are essentially hydrated gehlenite C₂ASH₈ and CSH_I with small quantities of C₄-AH₁₃. Investigations on metakaolinite obtained by calcination of three different raw-kaolinites show that the content of CSH_I in the cement at 28 days, thus the formation rate of this hydrate, depends on the mineralogical characteristics of the raw-kaolinite (grain size, nature of impurities, and chiefly crystallization state). In another hand, for a given Water/Cement ratio, it is pointed out that the higher the CSH_I content in the material after hardening, the higher the compressive strengths.