The influence of different additives on the working performance of ternary geopolymer grouting materials

Grouting is extensively employed in civil and hydraulic engineering, yet conventional cement-based grouting materials are associated with significant carbon emissions and limited constructability. Geopolymers, as a novel low-carbon binder, have been minimally explored for grouting applications. In this study, a ternary geopolymer grouting material was developed using sodium silicate solution as the alkaline activator and a precursor system comprising ground granulated blast furnace slag (GGBS), fly ash (FA), and metakaolin (MK). The effects of water-to-binder (W/B) ratios and chemical additives on the working performance of the geopolymer grouting material were systematically investigated. Firstly, increasing the W/B ratio significantly enhances workability and reduces plastic viscosity; however, excessive water content prolongs the initial setting time beyond permissible construction thresholds and degrades mechanical properties to substandard levels. Secondly, Response Surface Methodology (RSM) identified the optimal additive combination as 0.224 % calcium lignosulfonate (CL), 0.763 % nickel sulfamate (NS), and 0.803 % nickel ammonium sulfate (NAS). Under this formulation, the initial and 30-minute truncated cone fluidity increased by 10.8 % and 12.8 %, respectively, while the initial and 30-minute flow cone fluidity times decreased by 51.0 % and 56.6 %. The working performance and open time of the grout fully comply with the technical specifications for grouting materials outlined in the Chinese National Standard GB/T 50448–2015. Finally, microstructural characterization via X-ray diffraction (XRD), scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) confirmed the formation of dense reaction phases and homogeneous additive dispersion, providing mechanistic insights into the macroscopic performance enhancements. This study provides a replicable mix design methodology and theoretical foundation for developing low-carbon, high-performance geopolymer grouting materials with enhanced constructability. • Novel geopolymer grouting materials were developed using ternary precursors (GGBS, FA, MK) activated by sodium silicate, demonstrating sustainable and high-performance characteristics. • Critical water-to-binder ratio thresholds were identified: W/B < 0.2754 compromises workability, while W/B > 0.4029 degrades mechanical properties, with plastic viscosity inversely correlated to W/B ratio. • Additive synergy optimization revealed NAS as the most effective workability enhancer (order: NAS > NS > CL), with an optimal combination (0.224 % CL, 0.763 % NS, 0.803 % NAS) improving fluidity by 10.8–12.8 % and extending setting times by 52.9–61 %. • Multi-factor interaction insights from response surface methodology advanced the design of geopolymer grouts, balancing flowability, viscosity control, and extended workability for engineering applications.