Investigating the Effect of Silica to Alumina Ratios on the Chemical Structure of Metakaolin Based Geopolymers

This experimental study investigates the impact of different silica-to-alumina (Si/Al) ratios on geopolymers synthesized from metakaolin. Various ratios of Si/Al (1 : 1, 1.5 : 1, 2 : 1, 3 : 1, 4 : 1, and 5 : 1) were employed, nano-silica was the source material to alter the Si ratio. Microstructure and strength were analysed using SEM, XRD, NMR, and compressive strength testing Geopolymerization, a sustainable material synthesis process, was investigated using FTIR spectroscopy and computational modeling. The dissolution rates of aluminum and silicon molecules, as well as the formation of N-A-S-H gel, were studied. Results revealed that a Si/Al ratio of 2 : 1 significantly enhanced the dissolution of silicon and aluminum, leading to the formation of Si–O–T bonds and superior compressive strength. Computational analysis confirmed that the mechanical performance was primarily attributed to the formation of N-A-S-H gel, rather than zeolitic nuclei or silicate derivatives. These findings provide valuable insights for the application of geopolymerization in valorizing mine tailings, which often exhibit high Si/Al ratios.