Effect of nano-SiO2 on the alkali-activated characteristics of metakaolin-based geopolymers

The mechanical characteristics and structural properties of the products of alkali-activated metakaolin reactions are affected by the raw material composition and the concentration of alkali activator used. This study quantitatively analyzed the effects of the solid-to-liquid ratios and nano-SiO2 additions on the mechanical characteristics and flexural strength of metakaolin-based geopolymers to obtain optimal geopolymer proportions The weight and short-range network ordering of samples were examined using a thermogravimetric analyzer and Si-29 magic-angle spinning nuclear magnetic resonance. Nano-SiO2 particles with the average particle size of 10 nm were added up to 3 wt% to the geopolymer system and could accelerate the geopolymerization as a result of increased geopolymer gels amount and hence increased the flexural strength. The results show that a metakaolin-based geopolymer sample with a solid-to-liquid ratio of 1.03 containing 1% nano-SiO2 exhibited higher strength, higher density, and lower porosity than other samples. These characteristics are essential for understanding the mechanical strength, thermal stability, and fundamental structure of geopolymer systems. The results also indicated the potential for nanotechnology geopolymer applications. (C) 2013 Elsevier Ltd. All rights reserved.