In all electrochemical restoration techniques a direct current is applied between the reinforcement (cathode) and an external anode in electrolytic contact with the concrete. Cathodic protection (CP) is a permanent installation with design currents below 10 mA/m², electrochemical chloride extraction (or removal, - EC or ECR) and electrochemical realkalisation (ER) are applied only on a temporary basis and use currents up to 1 A/m². In all three cases the electrochemical reactions at the cathode (the rebars) produce hydroxyl ions leading to an increase of the pH near the rebar. This facilitates passivation of the steel. Reaction (1b) is possible at very high current densities and produces hydrogen and especially high tensile steels under load could suffer hydrogen embrittlement.

2 H₂O + O₂ + 4e ==> 4OH^-    (1a)    (at low current density)

2 H₂O + 2e^- ==> 2OH^- + H₂   (1b)    (at high current density)

Due to reactions on the anode (equations 2a, 2a’, 2b), the pH of solution around the anode will decrease. The acidification of electrolyte and formation of chlorine gas are considered to be undesirable. An acidic solution may attack the concrete and chlorine gas is toxic. Using alkaline electrolyte such as saturated calcium hydroxide solution or a sodium borate solution can prevent acid attack on concrete and chlorine gas formation. At pH above 7, practically no chlorine gas is formed as the reaction on the anode is predominated by reaction indicated by equation (2a’).