Fibre optic sensor systems for structural health monitoring of concrete structures

In Germany about 20 % of the publicly owned and more than 40 % of the privately owned sewerage tunnels are damaged. Therefore, it is essential to provide improved structural health monitoring SHM systems to predict such events before they occur and take mitigating action. We developed very simple and reliable fibre optic humidity and crack sensors to monitor the structural health of sewerage tunnels. The humidity sensors were fabricated by coating fibre Bragg gratings (FBGs) with Polyimide and applying a suitable packaging to withstand the harsh environment and are optimised to detect leakages at structure interfaces. The fibre optic crack sensors rely on carbon- or textile-based reinforcement structures with embedded optical fibres that can be incorporated into the building to, for instance, locate cracks along the structures due to excessive loadings. The sensors were characterised under simulated conditions in laboratory environment and subsequently integrated into municipal structures for long-term operation under real conditions. Future applications aim at the SHM of novel carbon- or textile-based concrete structures or bridges under static and dynamic conditions.