Optical fiber crack sensor for concrete structures

The condition of concrete structures can be assessed through the monitoring of crack openings. Researchers at MIT and Brown University have recently developed a novel concept for the sensing of cracks in concrete structures. The sensing capability is based on the light loss as microbending occurs in a fiber bridging the crack. To use the sensor, only the crack plane orientation in the structure (rather than the exact crack locations) needs to be known. With the use of OTDR, distributed sensing is possible. In this paper, the novel crack sensing concept is first introduced. To guide the design of sensors for various performance requirements, a theoretical model is developed to relate signal loss and crack opening. Prediction from the model is compared with experimental results. Using laboratory-sized specimens, the detection of both surface and interior cracks are demonstrated.