Durability of Reinforced Concrete under Impressed Current Cathodic Protection

Sammanfattning: Impressed current cathodic protection (ICCP) and prevention (ICCPre) are reliable and efficient techniques to stop, control and postpone corrosion in reinforced concrete structures. However, the wide application of this technique has been limited by the high cost of the anode system. Moreover, the long-term electrochemical effects on the anode-concrete interface and the steel reinforcement are still not completely clear. These effects can be beneficial or unfavorable, which will influence the performance and service life of the structure. Therefore, the long-term electrochemical effects greatly need to be quantified and taken into consideration in durability design. The present thesis has been devoted to gaining more solid scientific understanding into this issue through experimental work. A novel and affordable carbon fiber reinforced polymer (CFRP) mesh was used as anode material instead of traditional metallic anode. Accelerated tests, using relatively high current densities, were adopted to evaluate the long-term electrochemical effects. The impact of the accelerated tests was studied and modeled. Varied characterization and monitoring techniques were employed to analyze the anode-concrete interface and the steel condition as well as chloride content. The results show that the CFRP meshes are suitable as anode material for cathodic prevention applications, with a service life of more than 100 years. Calcium leaching at the anode-concrete interface was inevitable as a consequence of chemical reactions and mass transport under current exchange. The chemical changes can cause material loss and increase the resistance of the concrete and eventually make the system fail. With low current densities, the chemical changes can be significantly reduced. A nonlinear conversion model was proposed to estimate the performance under low current densities from the results of the accelerated tests. The difference between the nonlinear model and the linear model can be 30% to 40%. When the current density is less than 2 mA/m2, the service life regarding the anode-concrete interface can be longer than 70 years. For the critical chloride content, under a current density of 2 mA/m2, the critical value can be increased nearly by a factor of two and the service life against chloride ingress can be increased by a factor of seven according to the DuraCrete model under the specific modeling condition. Considering both the anode-concrete interface and the chloride content at the steel surface, it has been successfully proven that by applying low current densities, the service life of reinforced concrete structures can be significantly extended, to the range of 100 years or more. The cost of such ICCPre applications can be further reduced by using CFRP mesh anodes without compromising the performance of the system.