Introduction/Objective: Slag-based geopolymer slurry (GS) often suffers from rapid setting and limited fluidity, which are primarily attributed to its high CaO content and large specific surface area. These drawbacks restrict its workability and practical application in ambient-cured systems. To address these challenges, this study introduces fly ash as a co-precursor to modulate both the replacement ratio and the initial chemical composition of GS. Such adjustment simultaneously alters the physicochemical environment of the activating system, thereby influencing the balance between hydration and geopolymerization reactions. By clarifying this dual physical–chemical regulation, the present work not only provides fundamental insights into the synergistic reaction mechanism but also establishes a basis for the rational design of high-performance and potentially patentable geopolymer formulations. Methods: Composite precursors were prepared by replacing slag with 5-70 wt% fly ash, while dynamically adjusting the activator dosage to control the initial chemical composition (SiO2/Al2O3 and CaO/Al2O3 ratios). Fresh behavior tests, compressive strength measurements, and product characterization techniques, including XRD, FTIR, and SEM-EDS, were employed to evaluate the macroscopic properties and microstructural evolution of GS under ambient curing. Results: The introduction of fly ash improved fluidity, prolonged setting time, and optimized strength development through simultaneous effects of particle packing and chemical composition adjustment. A fly ash content of 30 wt% (S70F30) achieved the highest compressive strength (48.4 MPa at 3 days and 64.3 MPa at 28 days), attributed to balanced hydration–geopolymerization reactions and the formation of dense (C, N)-A-S-H gels. In contrast, excessive fly ash replacement reduced reactive components, weakened gel formation, and deteriorated matrix densification. Discussion: The improvement in GS performance results from dual mechanisms: (i) physical lubrication by spherical fly ash particles, enhancing packing uniformity, and (ii) chemical regulation of initial molar ratios, which shifts the reaction pathway and gel products. This interplay ensures stable strength development when the fly ash proportion and initial chemistry are both appropriately optimized. Conclusion: Incorporating 30 wt% fly ash with adjusted initial chemical ratios substantially improves the fresh properties and long-term strength of slag-based GS. These findings highlight the potential of composite precursor design in developing high-performance and sustainable geopolymer binders.
Luo et al. (Tue,) studied this question.