A fibre optic sensor for cracks in concrete structures

The condition of a concrete structure can be effectively assessed through the monitoring of cracks. Large cracks may be warning signs of severe degradation, while small cracks with openings from 0.2 to 0.4 mm may lead to durability problems associated with the penetration of water and other chemicals. Since the location of cracks in a concrete structure is not known in a-priori, conventional 'point' sensors (e.g., strain gauges) are not effective in the sensing of cracks. In this presentation recent developments on a fibre optic crack sensor that allows the detection and monitoring of multiple cracks without requiring prior knowledge of crack locations are described. After a discussion of the sensing principle, a theoretical model for signal loss vs crack opening is derived to provide guidelines for sensor design. The fabrication of a sensor suitable for both external bonding and internal installation in a concrete structure will be described. Representative experimental results will be shown and comparison with theoretical predictions is conducted. Based on the experimental and theoretical findings, the potential of the sensor for practical applications is demonstrated.