Studies of geopolymerization route for metakaolin geopolymeric materials

Investigation on production of metakaolin geopolymeric powder was aimed to increase the productivity and application of geopolymer products. Geopolymerization process was applied in the manufacturing of metakaolin geopolymeric powder to be used in geopolymer synthesis. Geopolymer slurry was made by alkaline activation of metakaolin in alkali activator solution (a mixture of NaOH and sodium silicate solutions). The geopolymer slurry was heated in an oven to produce pre-cured paste and then pulverized to get uniform particle size geopolymeric powder. By adopting the concept of “just add water”, the metakaolin geopolymeric powder was mixed with water and then oven-cured to produce resulting geopolymer pastes. The physical and mechanical properties of geopolymeric powder and resulting geopolymer pastes, such as workability, setting time, bulk density and compressive strength were studied. These geopolymeric powder and resulting geopolymer pastes were also characterized by using SEM/EDX, XRD and FTIR analyses. The results showed that the optimum conditions for producing highest strength resulting paste are by using 8M of NaOH solution, solids/liquid ratio of 0.80, an activator ratio of 0.20, pre-curing of 80°C for 4 hours, 22% of mixing water and curing regime of 60°C for 72 hours. The resulting geopolymer pastes have low bulk density and were potential for a lightweight material. Upon the mixing of water with geopolymeric powder, densification of the structure occurred with the formation of compact geopolymer gels. The geopolymeric powder and resulting pastes showed the combination of amorphous and crystalline phases as analyzed by XRD. After ageing, the intensities of zeolites crystalline phases increased and this emphasized the benefit of zeolites in strength development of resulting pastes. Moreover, FTIR analysis revealed the growth of geopolymer bonding with ages. The optimum SiO2/Al2O3, Na2O/SiO2, H2O/Na2O and Na2O/Al2O3 oxide-molar ratios were 3.10, 0.37, 14.23 and 1.15, respectively. Study on the oxide-molar ratios concluded that mechanical properties of geopolymer paste were influenced most significantly by Na2O/Al2O3 and H2O/Na2O molar ratios. This study clearly demonstrates that the production of metakaolin geopolymeric powder was able to be used in manufacturing geopolymer pastes.