Optical fiber sensors for monitoring ingress of moisture in structural concrete

Abstract

Fiber optic-based humidity sensors, fabricated using fiber Bragg gratings coated with moisture sensitive polymer, are employed in detecting and monitoring the movement of moisture through standardized cubes made from samples of different types of structural concrete. Data obtained can give information on the properties of different types of concrete and thus on the migration of dissolved salts, e.g., sodium chloride, which is important in view of their deleterious effects on reinforcement bars within concrete. To undertake the research, two such optical fiber sensors were placed at varying distances from the edge of the cube face to the inner part of the concrete sample and subjected to a constant head of water at a constant temperature. The optical fiber sensors reacted to the ingress of water by detecting the moisture migrating through the sample, indicated by a shift in the Bragg wavelength of the sensor.