Michio Imai

Crack Detection Application for Fiber Reinforced Concrete Using BOCDA-Based Optical Fiber Strain Sensor

Distributed optical fiber strain sensors have attracted increasing attention in research and applications related to civil engineering because no other tools can satisfactorily detect the locations of unpredictable events. For instance, for crack detection, it is necessary to employ a fully distributed sensor because crack locations are a priori unknown. The Brillouin optical correlation domain analysis (BOCDA) system, a distributed sensor that offers high spatial resolution by using stimulated Brillouin scattering, has undergone significant development over the last decade, during which it has been used in a wide range of civil engineering applications. In this paper, we demonstrate how a BOCDA-based optical fiber strain sensor can be employed to monitor cracks in fiber-reinforced concrete. Crack monitoring is important for checking the structure of such high-performance concrete, which has enhanced strength and toughness since it incorporates fibers. In particular, early detection of tiny cracks is essential for preventing crack growth and dispersion. We carried out a concrete beam-bending test to detect crack-induced strain distribution during loading. For this purpose, we employed an improved BOCDA system that provides enhanced measurement length with high spatial resolution; hence, BOCDA can detect a tiny crack before visual recognition. Moreover, we demonstrate a field application of the BOCDA system to ensure a flawless pedestrian deck made of fiber-reinforced concrete.