Electrical removal of chloride ions from cement-based materials.

摘要

This thesis is a fundamental investigation of the process of electrical removal of chloride ions from cement. The investigation involves the performance of electrical and chemical measurements on cement containing controlled concentrations of sodium chloride and subjected to the process at different current densities, different time periods and different electrode compositions. The process is found to be comparably effective for configuration I (both anode and cathode being ionic conductors, i.e., aqueous solution) and configuration II (the anode being an ionic conductor and the cathode being an electronic conductor). This means that the process can be implemented without using a steel rebar as a cathode, thus widening the applicability of this method of chloride ion removal. Both diffusion and drift are found to contribute to the electrical removal of chloride ions from cement. The contribution by diffusion (as high as 54%) tends to be larger for configuration I than configuration II. The contact electrical resistivity of the interface between the cement and an electrode (anode or cathode) is around 103 O.cm 2. It increases as the process occurs, such that the rate of increase diminishes as the process occurs. The fractional increase in contact resistivity in 300 s of the process is up to 10.6. The contact resistivity value is comparable at the anode and cathode for both configurations I and II. The pH value of the aqueous solution that serves as the ionic conductor at the anode tends to decrease as chloride ion removal occurs. However, it is not an effective indicator of the extent of chloride ion removal. Analysis of the chloride ion concentration in the solution by titration provides a more reliable indication.