Embedded fiber optic dual use sensing technique for concrete structure

The development of a fiber optic dual use sensor for embedding in concrete structure or buildings are described. The sensing system could monitor the state of a structure during construction and throughout its working life. The embedded optical fiber sensor, at first; can be employed as a transducer for measurement the temperature of fresh concrete at early age. Then, the embedded fibers do not degrade during curing, and they bond strongly to the matrix. The permanently embedded fiber optic sensors offers the opportunity to monitor the strain or displacements associated with the opening of the micro-cracks of the concrete structures in its whole life. In our experiments, a white light fiber optic interferometer is used to sense and measurement the temperature in a specimen concrete beam. A direct relationship between the fiber deformation and the optical path variation of the fiber sensor is obtained. A calibration procedure is developed by which the optical signal is converted to displacements. The temperature test results are compared with a convenience thermal couple. Experiments involved embedment of the optical fiber in concrete beams. In order to investigate micro-crack opening displacement characteristics, the sensor was employed in a series of fracture tests. Specimens were center-edge-notched and the fiber optic sensor with the gauge length L were embedded at the tip of the notch. This arrangement allowed for direct measurement of displacements associated with the opening of microcracks at the crack tip. Experimental results are presented and crack-tip opening displacement (CTOD) results are compared with crack-opening displacements (COD) measured by conventional transducers at the crack mouth.