Geopolymerisation kinetics. 2. Reaction kinetic modelling

A mathematical model for the kinetics of geopolymerisation is presented. The model includes explicit description of a complex multistep reaction process leading to a phase-mixed product. Silicate speciation equilibria are described by relationships derived explicitly from high-resolution 29Si NMR data, and an autocatalytic polymerisation step provides good agreement with the observed kinetics of geopolymerisation. Comparisons of model predictions with data from in situ energy dispersive X-ray diffractometry are presented, and the kinetic effects of different alkali metal cations (Na+Na+ or K+K+) and of variations in SiO2/Al2O3SiO2/Al2O3 ratio are seen to be described adequately by the model.