Indirect measurement of corrosion in reinforced concrete using optical sensor composed of polydimethylsiloxane/titanium oxide composite and sacrificial steel plate

Corrosion of reinforcing bars deteriorates the bond between the rebar and concrete, consequently leading to the degradation of the strength and stiffness of reinforced concrete. Because structural deterioration due to corrosion may cause failure and large-scale disaster, Query various methods of measuring the corrosion ratio (electrochemical methods, fiber optic sensors, strain gauge, ultrasonic wave, and infrared thermography) have been proposed so far. The electrochemical methods are the most widely used for estimating corrosion ratios but have the limitations that the measurement results are qualitative, and are affected by climatic parameters. To overcome these limitations, fiber Bragg grating sensors to directly detect the expansion displacement of reinforcing bars due to corrosion have been developed. However, these sensors are susceptible to strain induced by heat and external loads, and they also present challenges in terms of miniaturization and installation. This study developed a new optical sensor that can overcome the limitations of existing sensors. The developed sensor detects the expansion displacement of the sacrificial steel plate due to corrosion in order to indirectly estimate the corrosion ratio of rebar. A linear relationship between the displacement and the sensor response was observed, and the sensor was capable of measuring the displacement up to half the depth of the sensor. The sensor also showed a reversible response to repeated displacement and was stable even in alkaline and salty environments. Its practicality was also verified by accelerated corrosion tests.