Thermodynamic modeling of one-part-geopolymer binders based on fly ash and micronized dredged sediments
Elie Mahfoud, Khadim Ndiaye, Walid Maherzi, Salima Aggoun, Nor-Edine Abriak, Mahfoud Benzerzour
Abstract
In this study, a thermodynamic model was developed to perform numerical simulations on one-part-geopolymer binders based on fly ash and micronized dredged sediments to study the effect of several parameters on the composition of geopolymer material. First, the thermodynamic model was validated by experimental results. This validation consisted in comparing the rate of geopolymerization products obtained by the model with that obtained by experimental quantification based on deconvolution of the FTIR spectrum of geopolymer pastes. To better understand the experimental optimization, a numerical optimization is performed with the model, varying several parameters. Simulation results showed that an excess of alkali reagent could negatively affect the geopolymerization reaction, in line with experimental findings, due to chemical instability linked to the significant rise in pH. It seems that excess silicon ions in the alkali reagent solution limit the dissolution of the aluminosilicate, resulting in a decrease in the geopolymerization products rate accompanied by the appearance of unreacted sodium silicate. At the same time, the negative effect of excess added water on the reaction was proved. The addition of excessive quantities of water not required for the reaction leads to dilution of the alkalinity, which reduces the dissolution of the aluminosilicate’s sources, and therefore the potential formation of geopolymerization products. Finally, this model can be used to predict and to better understand the effect of several parameters on the final composition of geopolymer, thus reducing the number of trials required to study the effect of these parameters and optimize them. • A thermodynamic model was developed to predict the composition of one-part-geopolymer. • The model was validated using experimental quantification based on FTIR spectrum deconvolution. • The simulation shows an optimum for alkali reagent/binder, water/solid and Na 2 SiO 3 /NaOH ratios. • The excess of alkaline reagent negatively affects the geopolymerization reaction. • The C-A-S-H/N-A-S-H ratio increased with the Sediment/Fly ash ratio.