Effects SiO2/Na2O molar ratio on mechanical properties and the microstructure of nano-SiO2 metakaolin-based geopolymers

An alkali-activating solution plays an important role in dissolving Si and Al atoms to form geopolymer precursors and aluminosilicate material. This study explores the effects of the SiO2/Na2O molar ratio (1.0–2.0) on the properties of nano-SiO2 metakaolin-based geopolymers. The setting time, compressive strength, mercury intrusion porosimetry (MIP), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) are investigated to study the properties of the geopolymers. The results show that the compressive strength increased, and that the products of geopolymerization filled pores with curing time, causing the microstructure to become dense. Moreover, a nano-SiO2 metakaolin-based geopolymer sample with a SiO2/Na2O ratio of 1.5 exhibited more strength, higher density, and less porosity. Applying the nano-SiO2 to a geopolymer enhances compactness, improves uniformity, and increases strength.