Abstract:

Geopolymers, with good mechanical properties and resistance to acid attacks, were prepared using flyash and kaolin. Geopolymer could be equivalents of the Portland cement products. The mechanism of polymerization was deduced from the analytical data of XRD, IR, SEM, and NMR of the geopolymeric products cured each for 3 days, 7 days, 14 days, and 28 days, which can be described as follows:(1) the glassy parts of the flyash were dissolved in the high molar alkaline solution and some Si—O, Al—O bonds were broken; (2) at the presence of OH^- and Na⁺, these broken bonds formed aluminosilicate gel and then transformed into zeolitic precursors with changing compositions and concentrations of the solution; (3) by dehydration, these zeolitic precursors were changed into the amorphous phase materials. NMR analysis indicated that in the geopolymeric products cured for 28 days, Q⁴ was the principal form of Si element. The experimental results provided a good basis for understanding the reactive mechanism of polymerization during processing of geopolymer products.

Key words: flyash, geopolymer, aluminosilicate, polymerization mechanism