Interfacial changes of optical fibers in the cementitious environment

Abstract

Embedded optical fiber sensors have recently been employed for strain and crack monitoring in concrete structures. The performance of the sensor is strongly affected by the fiber/matrix interface. For strain monitoring, effective stress transfer between fiber and matrix is required. A high interfacial bond is therefore desirable. On the other hand, crack sensing may rely on fiber debonding and bending, which is only possible with a weak interfacial bond. In the cementitious environment, the interfacial properties are known to vary with time, and this may affect the long-term performance of embedded optical sensors. The objective of the present investigation is to study the interfacial changes when specimens containing embedded optical fibers (with different coatings) are subject to different environmental conditions including wet curing, wetting/drying and freezing/thawing. Fibers removed from the matrix are examined under the SEM. Also, fiber pull-out specimens are prepared and tested. The results show that the fiber pull-out test can reveal significant changes in interfacial behaviour that cannot be detected from SEM examination. The pull-out test is therefore demonstrated to be a useful technique for the characterization of time dependent interfacial behavior for embedded optical fiber sensors.