Low-coherent fiber-optic interferometry for in situ monitoring the corrosion-induced expansion of pre-stressed concrete cylinder pipes

The corrosion-induced expansion of pre-stressed concrete cylinder pipes shapes a major determining factor in the durability of most pipeline systems. However, a structure extended in a very large span and accompanied by a slow corrosion-induced structural damage is still a challenge in practice. Here, a low-coherent fiber-optic interferometry is proposed for in situ measuring the corrosion-induced expansion by directly circling the sensing optical fiber on the outer surface of the pipe. Since the accuracy of the absolute deformation measurement by the low-coherent fiber-optic interferometry can reach 3–5 μm, we are able to improve the sensitivity by choosing the length of the sensing fiber. In the experiment, we employ 50-m sensing fiber; therefore, a resolution of about 0.1 microstrains had been approached. We chose 12 places along the pipeline as the corrosion-induced expansion monitoring points. On monitoring for about half a year, a non-uniform interface in structure, such as the repaired places, was found as a key factor of the corrosion-induced expansion development, which could be a reference for the further health care of the pipeline structures.