Temperature and composition effects on fresh and hardened properties of slag-fly ash-silica fume alkali-activated...

Growing concerns over carbon emissions from traditional cement have intensified interest in alkali-activated materials (AAM) as sustainable alternatives. In grouting applications, key performance parameters such as strength, fluidity, viscosity, setting time, and bleeding rate are strongly influenced by both material composition and curing temperature. As underground engineering projects extend deeper, environmental temperatures gradually increase from ambient to 60 °C with depth, yet limited room-temperature studies on alkali-activated grouting materials (AAGM) cannot fully meet engineering requirements across temperature conditions. This study systematically investigated the effects of temperature (20 °C, 40 °C, 60 °C) and composition (including precursor ratios, activator modulus, and liquid-to-solid ratio) on the behavior of ternary slag-fly ash-silica fume AAGM. A comprehensive suite of characterization techniques, including XRD, FTIR, TG-DTG, SEM-EDS, ICC, NMR, MIP, and pH measurement, was employed to elucidate reaction behavior and microstructural evolution. Results indicated that elevated curing temperatures significantly accelerated early-age strength development and reduced setting time but decreased fluidity and increased viscosity. Microstructural analysis revealed enhanced precursor dissolution and the formation of more polymerized amorphous aluminosilicate networks at higher temperatures, accompanied by increased porosity and microcracking due to drying shrinkage. NMR results suggested a temperature-induced shift from low-coordination (Q¹, Q²) to higher-coordination (Q³, Q⁴) silicate species, indicating increased binder polymerization. The study proposed suitable parameter ranges and provided insights into temperature and composition mechanisms, facilitating AAGM formulation optimization under specific temperature conditions.