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Synthesis, characterization and relevant mechanisms of one-part geopolymeric cement by calcining low-quality illite clay with alkali

Meixun Peng, Zhenghong Wang, Shaohua Shen, Qiuguo Xiao

Precursors synthesized through thermal activation of low-quality illite clay with alkali (NaOH or Na2CO3) were hydrated by only adding water to synthesize one-part geopolymer pastes, and the strength and the microstructures of relevant specimens were characterized. An acceptable compressive strength was obtained when the hydrated specimens were cured at 80 °C for 3 d. Thermal decomposition of the clay is distinctly altered by adding alkali, and the octahedral-coordinatedAl turns into tetrahedralAl after calcination according to IR analysis. Besides illite,most of the quartz in the clay is converted to X-ray amorphous geopolymer precursors. The nepheline formed during calcination disappears at elevated temperature 950 °C. It is found that the compressive strength of one-part geopolymers is positively related to the content of nepheline in the clinkers. Partial dissolution of clinker particles in water facilitates cementing property. No crystal hydrate is found during hydration so the cementing mechanism is proposed to be X-ray amorphous zeolite-like gel as what in two-part geopolymers.