Preparation And Performances Of Chloride Ion Sensor For Concrete

Chloride is one of the major causes of corrosion of the reinforced concrete. It is therefore of great significance for real-time, accurate detection of chloride content in concrete. The traditional method of detection is time consuming, complicated operation and destructive. Up to now, large numbers of researches on embedded chloride ion sensor have been carried out, but the short service time, poor immunity to pollutants also limit its application. In this paper, Ag/AgCl electrode was prepared using silver foil as substrate. The experimental results show that the electrodes have good electrochemical response, and are suitable for detecting the content of chloride ions in concrete.Solid rolled Ag/AgCl electrode was prepared by electrochemical oxidation of silver foil, and then its potential response was checked in a simulated pore solution. After the rolled Ag/ACl electrode was immersed in the solution for 230 d, its potential fluctuation is less than 6mV. Meanwhile the electrode was proved to have a better linear response slope close to the theoretical value, a lower charge transfer resistance(70.9 ?), and large exchange current density, and high immunity to sulfide. The morphology analysis indicates that the rolled Ag/AgCl electrode has a higher active specific surface area, which improves the stability and sensitivity of the electrode. Moreover, the close stacked layer by layer of AgCl/Ag also enhances the adhesion force of the layer to the matrix, which further improves its reliability on chloride detection and its service life in concrete.MnO2 reference electrodes were assembled by cement semipermeable sheet, alkaline gel electrolyte and manganese powder using molding press method and the results show that, ?-MnO2 has higher electrochemical activity, the gel electrolyte also exhibit good water-retaining ability and electrical conductivity. Moreover, the addition of expanding agent in cement can decrease the resistance of the semipermeable sheet, the MnO2 reference electrode has strong anti-polarization capability even embedded in concrete.In order to improve the stability of Ag/AgCl electrodes in concrete, the electrodes was wrapped by the non-woven cloth coated with polyvinyl alcohol gel electrolyte and then embedded in mortar. During the curing age, the open circuit potential of the electrodes was found to be stable and exhibit a better linearity to log [Cl-]. When low content of sulfide and amine corrosion inhibitors was admixed in the mortar, the potential fluctuation of the Ag/AgCl electrode is still very stable. Compared to the chemical analysis, chloride ions concentration detected by the rolled electrodes are lower, but it can be calibrated through the coefficient of correction.we also prepared a carbon-based Ag/AgCl composite electrode, of carbon nanotube(CNT) and graphene, the potential stability of Ag/AgCl/CNTs electrode is rather stable even after 60 d, the slope of the linear response is 49.91 mV. Ag/AgCl/CNTs electrode has a lower charge transfer resistance and higher exchange current density, which could facilitate its application for the Cl- detection in concrete.