Effects of Liquid-to-Solid Ratio, Temperature, and Alkali Activator Concentration on Rheological Properties of Ternary Solid Waste Geopolymer

To investigate the rheological properties of geopolymer grouting materials, a systematic study was conducted on a slag–red mud–fly ash ternary solid waste geopolymer grouting material (TSWGGM). The effects of liquid-to-solid ratio (0.5–1.5), slurry temperature (10–50 °C), and alkali activator concentration (1.0–1.8 mol/L) on the rheological model, yield stress, time-dependent viscosity behavior, and thixotropy were examined. The results show that the liquid-to-solid ratio is the dominant factor determining the rheological model. With increasing liquid-to-solid ratio, the slurry exhibits Herschel–Bulkley (shear thinning), Bingham, and Newtonian fluid behaviors in sequence. The yield stress decreases significantly with increasing liquid-to-solid ratio and approaches zero at high liquid-to-solid ratios (≥1.0), while it increases with rising temperature. In the temperature range of 20–30 °C, the time-dependent viscosity curves follow an exponential growth law, whereas at 40–50 °C, competition between early reaction and shear destruction leads to an initial decrease followed by an increase in viscosity. At low alkali activator concentrations (≤1.4 mol/L), the time-dependent viscosity curves still obey the exponential model, but at excessively high concentrations (≥1.6 mol/L) a non-monotonic change (an initial increase followed by a decrease, and final steady growth) occurs. The thixotropic loop area decreases with increasing liquid-to-solid ratio, first decreases and then increases with rising temperature, and exhibits a critical phenomenon of first increasing and then decreasing with increasing alkali activator concentration.