Abstract: Metro concrete immersed in groundwater not only suffers from the dual corrosion of chloride and sulfate but also generally sustains stray current corrosion, leading to severe corrosion to the buried metal along the track and the reinforcement in the concrete structure. Existing research generally agrees that it is the free chloride ions remaining in the pore solution that causes the corrosion of the steel bar. When the chloride ions cannot be objectively prevented from invading the interior of the concrete structure, improving the binding capacity of the chloride ions can effectively reduce its harm to the reinforced concrete. In this work, the best combination scheme for enhancing the chloride binding capacity of the metro concrete is proposed by reasonably selecting mineral admixtures, types of polymers, and their corresponding amounts. The content of bound chloride ions was determined by potentiometric titration, and the optimized binding performance of the chloride ions in concrete was characterized utilizing XRD, SEM, and DTG. The results are indicated that metakaolin has the prior in the improvement of chloride ion binding capacity under stray current than silica fume, and fly ash micro-sphere outperforms zeolite powder. Also, the specimen mixed with 10% metakaolin, 20% fly ash micro-sphere, and 1.5% PVA re-dispersible emulsion powder has the best chloride binding capacity. The compounding of mineral admixtures and polymers significantly improves the binding capacity of chloride ions inside the specimen.
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