Physico-mechanical properties and leaching resistance of alkali-activated slag incorporating nuclear liquid organic waste

Nuclear liquid waste poses significant environmental risks and requires effective immobilization for safe disposal. Traditional cementitious matrices exhibit poor compatibility with hydrophobic organic wastes like lubricating oils, leading to low waste loading and reduced mechanical integrity. Alkali-activated materials have shown promise but remain underexplored despite their potential for scalability and sustainability. This study investigates the performance of alkali-activated slag (AAS) as a novel hosting matrix for immobilizing two lubricating oils (Nevastane EP100 and Shellspirax S2 80W90) at 20–25 vol.% loading, using Tween 80 surfactant and varying water-to-binder (w/b) ratios (0.35–0.55). Waste-forms were characterized for reaction kinetics via isothermal calorimetry, mechanical strength, density, accessible water porosity, water permeability, and leachability in 6 M NH₄NO₃ solution to simulate aggressive nitrate-rich environments and predict long-term behavior under groundwater exposure. Key findings reveal that oils delay early reaction but yield comparable cumulative heat release, indicating temporary hindrance. Mechanical strengths decreased (up to 60%) yet met Belgian waste acceptance criteria (>8 MPa compressive, >2 MPa flexural strength). Hydrophobic oils reduced apparent density and water-accessible porosity, while increasing permeability (∼17 times higher than reference AAS). Leaching depths (∼8–12 mm after 28 days of exposure) and elemental release (e.g., <3.3% of Ca, <8.7% of Na) were similar to pristine AAS, with minimal framework damage. Notably, Nevastane oil dispersed as irregular droplets with better retention, whereas Shellspirax formed segregated zones, leading to higher leaching. Post-leaching, permeability moderately increased due to microcracks and C-A-S-H alterations. This work highlights AAS's novelty as a robust, byproduct-based alternative for nuclear oil waste encapsulation, offering superior miscibility over cement. These insights broaden hosting options, emphasizing optimal formulations for enhanced waste retention and long-term stability, paving the way for sustainable nuclear waste management.