| 摘要 |
PROBLEM TO BE SOLVED: To detect a craze occurring at a place which is difficult to access. SOLUTION: Optical fibers 12 are previously embedded along the surface of one side face in a concrete 10. Each fiber 12 is given axial light transmission properties in advance, and can emit a light at each of all side faces. When detecting the craze A, a light source 16 is connected to one end side of the fiber 12 to emit a visible light to be incident thereto. The visible light is partly transmitted through a core, leaked to a clad side, so that the light is emitted at the side face over the entire length of the fiber 12. If the craze A, reaching the surface of the concrete 10, exists from the vicinity of the fiber 12 in a state, in which such a side face light emission occurs, the visible light emitted from the side face propagates to the surface of the concrete 10 via the craze A. Accordingly, the position of the craze A can be detected by visually recognizing it.
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