Effect of Metakaolin Content on the Deterioration Resistance of Concrete Made with Recycled Fiber-Reinforced Tailings Aggregate Under Freeze–Thaw Cycles and Sulfate Freeze–Thaw Cycles

To improve the mechanical properties and durability of concrete made with recycled fiber-reinforced tailings aggregate, the influence of metakaolin (MK) content on its properties was studied. Freeze–thaw cycle tests and sulfate freeze–thaw cycle tests were performed. Moreover, the service life of concrete under freeze–thaw cycles was predicted using the grey system theory. The findings showed that even a small quantity of MK can significantly enhance the compressive strength of concrete, with the highest strength observed at 10% MK content. Concrete’s ability to withstand freeze–thaw and sulfate freeze–thaw conditions was improved by MK, with effectiveness increasing alongside MK content. The grey system theory effectively predicts the relative compressive strength of concrete in freeze–thaw environments. The prediction results demonstrated that MK significantly extends the service life of concrete. This research investigates the properties of concrete made from MK and industrial waste and provides a theoretical basis for engineering applications in cold climates, saline soils, and marine areas in Northwest China. The findings provide a reference for promoting a circular economy and environmental protection.