A passivating oxide layer protects embedded steel reinforcement from corrosion. Over time, however, chloride and carbonation can cause the passivating oxide layer to deteriorate, leaving rebar open to corrosion. One way to rehabilitate concrete that has been corroded by carbonation is to remove the contaminated concrete and expose the corroded rebar so corrosion can be removed. Another newer option stops corrosion by drawing chloride ions out of contaminated concrete and restoring the high pH level. This process can restore concrete in 10 days to 10 weeks, according to its developer.
The electrochemical process works by creating an electric field between reinforcing steel (the cathode) and an external anode attached to the concrete surface and embedded in an electrolyte. Applying the electric field to the external anode causes chloride ions to migrate toward the external anode, ending in the electrolyte paste and on the anode surface. Simultaneously, alkali ions move from the electrolyte paste into the carbonated concrete. Alkali also forms on the rebar. This realkalinization gradually restores the high pH level around the rebar and in the concrete cover. With the pH level restored, the passivating oxide layer can reform on the rebar and protect it from corrosion.