Applications of a distributed fiber optic crack sensor for concrete structures

The degradation of concrete structures is always accompanied by the formation of cracks. If cracks are detected at an early stage before significant degradation occurs, life of the structure can be extended by the performance of relatively low cost but timely maintenance measures. To detect and monitor cracking in concrete structures, where the crack locations are often not known in a-priori, a distributed optical crack sensor based on OTDR measurement of bend loss has been developed. In this paper, the sensing principle will be discussed and the fabrication of sensors for surface attachment and internal embedment is described. Experimental results are shown to demonstrate that the optical power loss versus crack opening relation at a particular point of bend loss is independent of the number of bends along the fiber. Then, the monitoring of single and multiple cracks under quasi-static loading is illustrated, followed by the detection of cracks under restrained dimensional change (caused by shrinkage or thermal effects). Finally, the sensor performance under cyclic loading is studied. Based on the test results, the potential of the sensor for practical applications is demonstrated. (c) 2006 Elsevier B.V. All rights reserved.