Microstructured optical fiber based chloride ion sensing method for concrete health monitoring

Chloride erosion is the main factor to decrease durability of concrete, it is fairly important to control and monitor chloride in concrete structure. A new sensor based on a suspended core optical fiber was developed to detect the chloride in concrete, in which lucigenin is selected as a fluorescence sensitive material for chloride. A novel type of the sol-gel membrane was introduced to immobilize lucigenin onto the inner wall of the suspended core optical fiber with dip-coating method. The properties of the sol-gel membrane were characterized by scanning electron microscope (SEM) and Fourier transforming infrared (FT-IR), and energy of evanescent field the suspended core optical fiber was calculated by using COMSOL. The fluorescence fluctuations of the optic fiber sensor are chloride concentration-dependent and the relationship between relative fluorescence intensity and chloride concentration follows the Stern-Volmer equation. The linear calibration formulas I0/I = 1 + 1.463[Cl−] (R2 = 0.973) and I0/I = 1 + 1.982[Cl−] (R2 = 0.984) with the detection limit of 0.02 M are obtained through detecting standard KCl solution and concrete simulated pore solution of KCl (pH = 13.5), respectively. Besides, specificity of the sensor is also tested.