Cracks Detection During Early-Age Concrete Hydration Using Distributed Fibre Optic Sensing: From Laboratory to Field Applications

The article summarises the recent examples in distributed fibre optic sensing (DFOS) as a non-destructive approach for crack detection, especially during the hydration of early-age concrete. Thanks to the application of appropriate measurement technology (like Rayleigh scattering), the DFOS tool (e.g. monolithic and composite sensors with reduced axial stiffness), installation procedures (both for the surface and embedding inside the concrete) and finally, the post-processing algorithms, it is possible to detect all the (micro)cracks and estimate their widths. The qualitative and quantitative analysis based on DFOS strain measurements provides new possibilities for the structural assessment of concrete and reinforced concrete structures. Cracks formed during the thermal-shrinkage phase of the concrete structures in the first days of hardening are crucial for their later performance and final durability. Thus, knowing the actual crack state is of great practical importance. The paper provides guidelines for good practices in developing such measurements, including the design of the strain sensors being installed within the concrete. These considerations are supported by the example applications in the laboratory, including small-size concrete specimens and full-size reinforced concrete beams. Finally, the deployment within the real railway bridge was presented, and example results were discussed.