Fiber Bragg Grating Sensor to Measure Relative Humidity in Concrete

Foster-Miller, Inc. proposes to develop a system for monitoring the internal relative humidity (RH) in concrete using an innovative optical fiber strain sensor. Capable of measurement from 70 to 100% RH, with precision of ? 1%, our approach builds on the technology already developed for strain sensors and fiber optic read-out systems. Since fiber optic sensors can be frequency multiplexed, approximately 100 sensors only about 100-micron diameter can be placed on a single optical fiber. The moisture inside concrete must be kept high during the hydration reaction while the cement gains its adhesive properties. For this reason, internal relative humidity in concrete is a critical measure of its strength or weakness. During the service life of the concrete structure, humidity will be a leading indicator of damage, and will provide information that will allow corrective action to be taken. Our new sensor will provide the sensitivity and chemical resistance to alkaline environments (pH~13) and the humidity sensors embedded in concrete will not consume power, as the measurement will be made from the end of the optical fiber. Foster-Miller will meet FHWA¿s strategic goals of mobility, productivity and safety through more accurate information on internal condition of fresh concrete.