Performance evolution of concrete modified with high-concentration saline effluent: From mechanical properties to freeze-thaw durability enhancement

High-concentration saline effluent (HS), a typical byproduct of coal mining, poses substantial environmental challenges because its harmful dissolved solids are present and exhibit complex ionic compositions, primarily Na+, Cl-, and SO42-. Herein, high-concentration saline effluent concrete (HSC) is prepared by incorporating HS as one of the solidification components. The effects of different HS contents (0 wt%-10 wt%) on the fresh-state properties, mechanical properties, and freeze-thaw (F-T) durability of HSC are systematically characterized. The performance evolution and phase composition were investigated through X-ray diffraction and field emission scanning electron microscopy. Additionally, the modified effects of fly ash incorporation on HSC performance were evaluated. These results showed that HS incorporation substantially modified the hydration kinetics of cement. At an optimal HS content of 4 wt%, the early-stage hydration of the C3S and C3A phases accelerated significantly, increasing of 23 % and 20 % in compressive and flexural strengths, respectively. However, excessive HS incorporation (>= 8 wt%) under F-T cycling negatively impacted durability, evidenced by severe surface spalling and a significant drop in relative dynamic modulus (below 60 %) after 100 cycles. The incorporation of fly ash at an optimal dosage of 25 wt% significantly enhanced the matrix densification and interfacial transition zone bonding performance of HSC, effectively improving its mechanical properties and F-T resistance. Finally, an HS ion transport model was proposed, and the freeze-thaw damage mechanisms in HSCs were elucidated. This study provides a novel approach to HS utilization and is expected to guide the practical implementation of HSC.