Fluorescence-Based Fiber Optic Sulphate Sensor for Long Term Sulphate Ion Monitoring in Concrete Structures

Abstract

Concrete has been one of the most popular construction materials around the world. However, sulphate ion will cause of concrete degradation and lead to the decrease of service life of concrete structures. The formation of ettringite and other reaction products can lead to the decrease of service life of concrete structures, thus, a continuous monitoring of sulphate ions is needed as a reference for the maintenance work of concrete structures. This paper presents the design and development of a fluorescence-based fiber optic sulphate sensor for this purpose. The sensor's design capitalizes on the changes in fluorescent intensity of morin-metal ion complexes induced by sulphate concentration changes. By using cellulose acetate, the complex is transformed from a solution to a thin film, serving as the sensing element in the sensor probe. The sensor provides a response over a sulphate molarity range of 0 mol/l to 0.010 mol/l. And after being embedded inside the cement paste, the sensor still responds to sulphate. These features make this fluorescence-based fiber optic sulphate sensor potentially suited for in field and long-term monitoring of sulphate ions in the concrete structures, thereby enhancing structural health monitoring within the civil engineering sector.