Development of alginate gel nanosphere-based fluorescent fiber optic sensor and its application in chloride ion monitoring of cement paste

Fluorescent optical fiber sensors offer a promising non-destructive approach for chloride ion monitoring in reinforced concrete structures, though challenges such as dye leakage and reducing reusability hinder their practical application despite advantages in sensitivity and electromagnetic interference immunity. To address these issues, this study developed a fluorescent fiber optic sensor for non-destructive detection of chloride ion concentration in cement-based materials. By synthesizing fluorescent nanospheres of calcium carbonate-encapsulated Rhodamine 6G through nano-encapsulation technology, dye leaching was effectively prevented, and a chloride ion-sensitive membrane was fabricated and integrated into the fiber optic probe. The constructed sensing system exhibits excellent performance: a measurement error of <3 %, reusability of 9–10 times, and a rapid response time of only 6 s. Practical monitoring demonstrated that the sensor can track chloride ion penetration behavior in cement paste in real-time within the range of 0.001–0.3 M. This technology provides a novel method for durability monitoring of concrete structures, offering significant engineering application value.