Mix proportion optimization of high ground temperature anti-dispersion grouting materials based on RSM

To address the susceptibility of conventional grouting materials to dispersion and their limited long-term strength development under high-ground-temperature and flowing-water conditions, a novel alkali-activated anti-dispersion grouting material was developed by taking advantage of the rapid strength development of alkali-activated binders under high-temperature curing. Ground granulated blast-furnace slag and red mud were used as precursors, sodium silicate solution as the alkali activator, and xanthan gum as the anti-dispersion agent. Based on the Box-Behnken design (BBD), the individual and interactive effects of activator concentration, liquid-to-solid ratio, and xanthan gum dosage on grout fluidity, setting time, anti-dispersion performance, and compressive strength were investigated. Regression models relating the influencing factors to the response variables were established, and the optimal mixture proportion of the grout was determined through multi-objective optimization. The time-dependent viscosity behavior of the optimized grout and the AC impedance spectroscopy properties of the hardened grout were further investigated. The results showed that, in addition to the significant effects of the individual factors on the response variables, several interaction terms were also significant. A linear model was used to describe fluidity, whereas quadratic polynomial models were adopted for the other response variables. The coefficients of determination of all the models exceeded 0.98, indicating that the models were reasonable and reliable. The optimal overall performance of the grout was achieved at an activator concentration of 57%, a liquid-to-solid ratio of 1.0, and a xanthan gum dosage of 0.55%. The relative errors between the measured and predicted values were all less than 5%, demonstrating the high predictive accuracy of the models. The optimized grout exhibited an exponential increase in viscosity, characterized by good pumpability at the early stage and rapid thickening at the later stage. AC impedance spectroscopy showed that, as the curing age increased from 3 h to 7 d, the high-frequency intercept of the impedance spectrum increased, indicating a gradual transition of the internal structure from a loose state to a dense state. This structural evolution verifies the mechanism underlying strength development and demonstrates the excellent early-strength performance of the proposed material.