Study of polycondensation process of metakaolin-based geopolymeric cement using semi-empirical AM1 calculations

In the present study all possible reaction pathways involved in the polycondensation process of metakaolin-based geopolymeric cement were systemically discussed according to thermodynamic theory. The reaction energy of every possible polycondensation pathway was also calculated using the semi-empirical AM1 method. The optimum polycondensation pathway was analysed on the basis of the energy-minimised principle. The calculation results showed that framework clusters should be primary polycondensation products of geopolymeric cement made with NaOH or KOH-activated metakaolin, which was also verified by nuclear magnetic resonance spectroscopy equipped with magic angle spinning technique. In addition, the semi-empirical AM1 calculations revealed that the existence of sheet polycondensation clusters was also possible, the amount of which depended on the types of alkaline solution.