6-Methoxyquinoline immobilized nylon sensor for monitoring chloride concentration in reinforced concrete

An excess in the threshold concentration of chloride in concrete leads to the initiation of reinforcement corrosion, which in turn results in a reduction in the load-bearing capacity of reinforced concrete (RC) structures. Accordingly, the chloride concentration of RC is periodically investigated via a destructive method, but this process is time-consuming, labor-intensive, and costly. In order to overcome the limitations, this study sought to develop an optical chloride sensor that can be used in structural health monitoring. To this end, nylon was functionalized using formaldehyde and epichlorohydrine, after which 6-methoxy quinoline was covalently immobilized to manufacture a sensor. The developed sensor was found to be capable of measuring chloride concentrations (0–5,000 mM) and exhibited rapid responsiveness and reversibility. In addition, the developed sensor also showed a stable response even when exposed to the pH 13.4 environment for three months, and it could detect changes in chloride concentration even inside the mortar.