Alkali Activation of Russian Calcined Medium-Grade Clay: Influence of NaOH Concentration

Abstract

The object of this study was to investigate how 5–14 M NaOH concentrations affect the mechanical properties, amorphous-crystalline phase transformations, and composition of the reaction product of alkali-activated calcined kaolinite/montmorillonite cement with reactive phases of 48%, and with the SiO2/Al2O3 ratio 1.62. The hardened pastes based on calcined clays showed the highest compressive strength following their activation with 8 M NaOH. The zeolite content in the alkali-activated calcined clay cements peaked at 11 M NaOH, and the corresponding Na2O/SiO2 and Na2O/Al2O3 molar ratios were 0.6 and 0.93, respectively. The main reaction products in the studied alkali-activated calcined clay cements were N-A-S-H, zeolite A, faujasite-Na, analcime, and sodium aluminium silicate hydrate. The obtained properties and reaction products facilitate the use of the proposed alkali-activated calcined clay materials for controlled low-strength materials, matrices for immobilization of radioactive wastes.