Study on the Kinetics of Geopolymerization

Geopolymer is defined as the chains or networks of mineral molecules synthesized by a reaction of aluminosilicate mineral with alkali activator solution. It possesses good chemical and mechanical properties and has a great potential to be used in various application. The aim of this research is to conduct a study on the kinetics of geopolymerization by applying Avrami's kinetics theory. The study focused on the effect of curing temperature and concentration of sodium hydroxide (NaOH) solution on geopolymerization. Setting time of fresh pastes and compressive strength of hardened pastes were determined using vicat needle test and compression machine respectively. Chemical dissolution method was used to determine the degree of reaction on hardened pastes. The samples were tested at different age of curing period which were 1, 7 and 24 hours. Avrami's kinetics theory was applied to analyze the geopolymerization profile. Based on the kinetics study, the growth rate (K) slightly increased from 0.51 to 0.54 and crystall shape (n) value slightly decreased from 0.472 to 0.460 with the increased in NaOH concentration from 8 M to 10 M. As the curing temperature was increased from 60 to 80°C, K decreased from 0.258 to 0.237 and n increased from 0.152 to 0.460. Higher n value indicated better crystall formation. While lower K value indicated the reaction rate is faster which resulted in geopolymer with better properties.