Elucidating cesium solidification and stabilization mechanisms in nano-gamma-alumina modified cementitious matrices under realistic conditions

Ordinary Portland cement (OPC) matrices are widely used in low and intermediate level radioactive waste immobilization; however, improvements in waste loading, workability, durability, and radionuclide retention remain desirable. This work investigates the influence of nano-γ-Al₂O₃ modification on the short-and long-term solidification and stabilization performance of OPC-based cesium-bearing waste forms under ideal and realistic curing conditions. The synthesized nano-γ-Al₂O₃ particles exhibited mesoporous morphology, reactive hydroxylated surfaces, and negative surface charge suitable for cementitious applications. Under ideal curing conditions, nano-γ-Al₂O₃ displayed a non-monotonic dosage-dependent effect on the hydration and solidification behavior due to multi-variable interactions leading to changes in the nano- and matrix-chemical conditions thus affecting the pore-solution chemistry, and hydration pathways. 5 wt.% modified matrix provided improved workability, enhanced volumetric stability, and acceptable mechanical performance. Under realistic curing conditions and maximum waste loading, the 5 wt.% nano-γ-Al₂O₃ matrices maintained their favorable processing. Mineralogical, spectroscopic, and microstructural analyses revealed the formation of Al-rich hydration assemblages, including AFt, AFm, and hydroxo-AFm phases and the presence of more hydroxylated species in the modified matrix. Elemental-ratio distributions in pristine and leached matrices indicated that Cesium binding is primarily associated with C-S-H/C-A-S-H and AFt/AFm hydration products. The results demonstrate that while nano-γ-Al₂O₃ effectively tailors the workability and hydration pathways under representative waste-conditioning conditions, its implementation involves a performance trade-off between processing behavior, mechanical integrity, and long-term cesium retention.