Physical and mechanical properties and micro characteristics of fly ash-based geopolymers incorporating soda residue

Geopolymer, emerged as an eco-friendly alternative to conventional cement binders, has distinct advantages of high mechanical and durable properties. Soda residue (SR), an alkaline and calcium-containing industrial solid waste, is produced from the Ammonia soda process of Na-2 CO3. Incorporating proper amount of soda residue for the preparation of geopolymer is promising to improve the overall performances and eco-friendly potentials of materials. In this study, fly ash based geopolymers were prepared to validate the feasibility and effectiveness of adopting SR. Five curing conditions were applied to fmd the optimal approach to reach the best physical and mechanical properties. The flexural and compressive behaviors were measured and evaluated. Then, the mineralogical phases, morphology and elemental component of gel products were probed through X-ray diffraction spectrbscopy (XRD) and scanning electron microscopy (SEM) coupled with energy-dispersive spectroscopy (EDS). Thereafter, the Fourier transform infrared spectrometer (FTIR) and Si-29 nuclear magnetic resonance (Si-29 NMR) were performed to investigate the geopolymerization of chemical bonds of geopolymers with and without SR. At last, the thermal stabilities of geopolymers were investigated by thermo-gravimetric/differential thermal synchronous thermal analysis spectrometer (TG-DSC) to check the decomposition of aragonite and calcite from SR. Results demonstrate that geopolymers containing 90 g SR (against 360 g fly ash) can acquire low shrinkage, early strength, good thermal stability when exposed to the curing condition of room temperature with sealed treatment. These results provide experimental basis and reference for the performance optimization of geopolymer materials and scientific resource utilization of solid waste SR.