Integrated Fiber Optic Sensors For Nondestructive Characterization Of Concrete Structures
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ABSTRACT It is possible to monitor the initiation and progress of various mechanical or environmentally induced perturbations in concrete elements by way of fully integrated optical fiber sensors. Geometric adaptability and ease by which optical fibers can be embedded within concrete elements has led to the development of a number of innovative applications for concrete elements. This article is intended for a brief introduction into the theories, principles, and applications of fiber optic sensors as they pertain to applications in concrete.. However, due to the fact that the transduction mechanism in optical fibers is invariant of the materials employed, the principles introduced here also correspond to other structural materials. The only application related differences among various materials pertain to sensitivity and choice of optical fiber sensor types.
INTRODUCTION Quality of a good concrete structure depends on good construction practice. On the other hand, continuous maintenance and repair preserves the quality of construction. Nondestructive testing and evaluation (NDT & NDE) provide relevant means for periodic inspection in order to
maintain the quality of constructed facilities. Early detection of large displacements and cracks in concrete elements will result in increased safety and considerable savings in rehabilitation costs. Optical fiber sensors are emerging as superior nondestructive means for evaluating the condition of concrete structures. In contrast to existing nondestructive evaluation techniques, optical fibers are able to detect minute variations in structural conditions through remote measurements. Fiber optic sensors are usually classified in terms of the transduction mechanism, and they are either intensity, wavelength, or phase based in construction. The measurand, i.e. strain, induces a change in the intensity, wavelength, or phase of the light propagating in the sensing region of the optical fiber. This change, in turn, is related to the measurand through the interrelationship between the optical phenomena and the specific measurand. The choice of approach usually depends on the specific application and requirements of the sensor. In general, optical fibers are very sensitive and provide large dynamic range. They are intrinsically immune to electric and electromagnetic interference, and geometrically flexible. The smart material concept takes advantage of the geometric adaptability of optical fibers. The most attractive feature of fiber optic sensors are their inherent ability to serve as both the sensing element and the signal transmission medium, allowing the electronic instrumentation to be remotely located from the measurement site. Incorporation of the fibers during the processing stage also offers the opportunity to monitor the condition of structural elements during fabrication.
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Mat. Res. Soc. Symp. Proc. Vol. 503 © 1998 Materials Research Society
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