Sustainable high-performance injection geopolymers, role of GGBFS and water-to-binder ratio in strength, microstructure, and predictive modeling

This work designed and optimized geopolymer injection mixtures suitable for curing under ambient conditions using fly ash (FA) and ground granulated blast furnace slag (GGBFS) as industrial waste-based binders. Water/binder (w/b) ratios were systematically tested in the range of 0.50-1.50, and 12 M sodium hydroxide (NaOH) together with sodium silicate (Na₂SiO₃) were used as activators, with the activator/binder and Na₂SiO₃/NaOH ratios fixed at 0.4 and 2.5, respectively. Sustainable industrial by-products have been combined with a systematic mix design to provide environmental benefits under mechanical efficiency and practical curing conditions. The effects of GGBFS content and w/b ratio on setting time, flow time, and compressive strength have been evaluated to determine optimal mixes for practical injection applications. To achieve early-age strength without requiring high-temperature curing, GGBFS was selected. Analysis of Variance (ANOVA) was applied to validate the parameters. The Marsh flow cone test was conducted to evaluate the injectability of the mixtures, and flow times were recorded. Compressive strength tests demonstrated that mechanical performance was greatly enhanced by increasing the GGBFS content, especially at low w/b ratios. With a strength of roughly 67 MPa, the GP-0.5 mixture (w/b = 0.50, 50% GGBFS) produced the best results regarding binder interaction and dense matrix formation. On the other hand, greater porosity was found to cause a loss in strength at high w/b ratios (> 1.0). Microstructural experiments (FE-SEM and EDX) revealed that compact gel phases occurred, and Ca-Si-Al-rich phases improved structural strength. The formation of aluminosilicate networks and the chemical evolution of the binder matrix were supported by the distinct vibration bands observed in FTIR and the crystal/phase analyses determined by XRD.