High-resolution high-sensitivity crack monitoring in concrete structure using distributed fibre optic sensors

A method designed to characterize cracks in concrete structures using a distributed fibre optic sensor technique is presented in this paper. High spatial resolution, high sensitivity strain mapping using a single optical fibre and Optical Frequency-Domain Reflectometry (OFDR) interrogator scheme was obtained in a structural test segment. Large strain values around the crack location indicate strain concentrations which can be linked to crack width and depth. The OFDR interrogator permits distributed sensing, and has the advantage to measure hundreds of local strain values per single string of sensing fibre. Fibre Bragg gratings are inscribed at a nominal frequency, greatly simplifies sensor interrogator design. We demonstrated the technique can detect cracks far before they become visible to the naked-eye, over a sensor length of tens of metres at a discrete measurement pitch as small as 0.5 cm, at a scan rate of every few seconds. (author)