Fibre Optic‐Based Patch Sensor for Crack Monitoring in Concrete Structures

ABSTRACT In the context of the necessity to monitor civil engineering structures for accident prevention, this paper presents the performance of an innovative optical fibre patch sensor that can be embedded or glued on the concrete's surface. The sensor is composed of a fabric comprising an optical fibre network. When employed in concrete structures, it is capable of detecting opening cracks in the order of 0.01 mm, thereby satisfying the regulatory standards for limit states (Eurocode 2). This sensor is capable of accurately tracking the evolution of crack, including cyclic changes, by sensing both the increase and decrease in crack width. The procedure outlined in this paper includes a preliminary investigation into the influence of fibre diameter and density within the patch, which has revealed that fibres of 750 μm in diameter exhibit optimal performance, as well as the attachment method to concrete surfaces. Subsequently, the process of calibration is detailed, followed by numerous laboratory tests that were conducted on reinforced concrete samples of varying sizes. Comparisons and validations of optical fibre patch sensor measurements were performed using digital image correlation, resulting in a sensitivity of the sensors reaching 0.01 mm/K, and an accuracy ranging between 0.1% and 1%. The discussion within this paper considers the installation of this new sensor both externally and internally within real reinforced concrete structures.