178 / 2022-04-30 16:39:37

The study on the pretreatment of Cathodic Protection applied to concrete structures cracked due to corrosion

Cathodic protection,Practical pretreatment,Corrosion,Corrosion crack,Injection method

Cathodic Protection (CP) is known well as an effective corrosion prevention method for concrete structures. This method needs pretreatment that treat some factors disturb CP current from anodes to rebars (Fig. 1). Cross section repair is often used as a pretreatment for concrete members that corrosion cracks occurred, while it is too much repair in some cases. In this paper, the possibility was shown that injection method can be used as a pretreatment targeting not so severe corrosion cracks. It found from the experiment and the numerical simulation that the injected material improve conductivity inside concrete and the part of the rebar where current reaches can be protected well.



In this experiment, 2 types of concrete specimens were prepared to consider the protection ability of CP with injection method (Fig. 2). Both of them were split into two parts and integrated again with FRP bolts to simulate a horizontal corrosion crack (Fig. 3). Mortar was pasted between 2 rebars without touching the rebars directly in one specimen (Specimen-I) to simulate the situation that a part of the crack was filled with an injection material, while the other was only split and integrated (Specimen-N). After CP test, Specimen-I showed a better protection result than Specimen-N on the upper side of the rebars due to much current through the injected part. Lower parts of the rebars were corroded seriously in the both specimens due to the bond loss between rebars and concrete. It was considered that the splitting of the 2 specimens simulated too serious corrosion cracks like that the concrete will be peel off soon.



Numerical simulations of CP were conducted to consider about CP effects in more practical cases than the experiment. There were 2 changes in the simulations from the experiment. First was the existence of the bond between rebars and concrete on the lower parts of the rebars. Corrosion crack is generated by the expansion pressure of the corroded rebar, and the bond remains up to the corrosion crack progress enough, that is concrete peeling (Fig. 4). Second was the polarization curves of rebars that reflects corrosion severity. Some stages of corrosion severities were simulated using the polarization curves obtained from mortar specimens simulated some stages of corrosion. It was found that rebars can be protected well in the case that the bond remains and corrosion is not serious except for the area facing to the cracks.



Based on the revealed possibility of the injection method as a pretreatment of CP, a research was conducted about the designs of an electrical cell for CP in a concrete member that including some parts repaired with injection method. Current distribution was revealed in such a case that some kinds of pretreatment were include in one member. In addition, it was shown that the injection method can be improved using electrolyte solutions at to fill around the rebar and enhance the conductivity inside. This research further can lead to researches about more detail pretreatment correspond to the deteriorations of structures, environment conditions, and more practical usage of CP as a result.