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The steel reinforcement in concrete structures is susceptible to corrosion when chloride ions enter into the concrete from de-icing salts applied to the concrete surface, or from seawater in marine environments. If chlorides are present in sufficient quantity, they disrupt the passive film on the reinforcing steel, resulting in corrosion. Oxygen content, moisture availability and temperature also affect this corrosion rate. Corrosion of the reinforcing steel can weaken the structural strength, create cracking, delaminating and spalling of the concrete. In concrete structures multi depth sensors may be used to assess the depth of chloride or carbonation ingress, and optionally the instantaneous corrosion rate. The multi depth sensor has four (4) galvanic couples of mild steel and stainless steel. These couples are located at four depths from the concrete surface, with the couple furthest from the surface placed above the rebar. A zero resistance ammeter (ZRA) is used to measure the current flow between the two electrodes. An increase in current flow indicates the ingress of chloride contamination and increased corrosivity at that electrode level. As an option, the Multi Depth Sensor can measure the instantaneous corrosion rate of steel in concrete by the method of Linear Polarization Resistance (LPR).