Tailing sand as sustainable aggregate: Enhancing durability of cast-in-situ concrete against combined sulfate-chloride attack

Tailings sand refers to the relatively fine-grained residue left behind after separating concentrate during mineral processing. This study conducts an in-depth analysis of the mechanism underlying the influence of tailings sand (TS) on the performance evolution of cast-in-situ mortar under composite sulfate and chloride corrosion conditions. The environmental conditions examined include four typical scenarios: distilled water, internal corrosion, external corrosion, and combined internal and external corrosion. Through long-term monitoring of the macro-mechanical degradation patterns and microstructural changes of cast-in-situ TS mortar (TS-CISCM) specimens under immersion conditions, it was found that in external or internal sulfate-chloride environments, the addition of 50 % TS significantly enhances the mechanical properties, increasing the compressive strength of the specimens at 180 days of curing by 25.7 % and 6.4 % compared to the distilled water group, respectively. However, when subjected to combined internal and external corrosion, the addition of 50 % TS may exacerbate specimen size expansion and weight loss due to promoting the formation of external ion penetration pathways and the generation of expansive corrosion products. Overall, TS could slow down corrosion reactions and significantly inhibit durability degradation by optimizing aggregate gradation and improving matrix density. Environmental assessment found that TS can not only serve as a viable substitute for river sand, but also exhibits superior material properties. The predictive model established can better predict the compressive strength of corroded samples (R2 = 0.98). The above conclusions provide quantitative evidence and technical pathways for the resource utilization of TS in high sulfate-chloride regions such as salt lakes and saline-alkali soils.