Effect of macrocell currents on rebar corrosion in reinforced concrete structures exposed to a marine environment

Abstract

Autonomous corrosion monitoring systems in reinforced concrete structures tend to use sensors that are electrically isolated from rebars. This monitoring strategy ignores the macrocell currents that take place between active and passive areas of reinforcement. The effect of these currents has been studied on rebar corrosion in structures exposed to a marine environment. The results showed the existence of macrocell currents generates greater anodic polarisation in rebars’ active areas, which favours chloride migration towards steel surface. As a result, corrosion onset takes place sooner, the concentration of the chlorides is higher, and the corrosion rate increases. When a rebar is in passive state, steel mass loss is negligible due to macrocell currents. However, after corrosion onset, the influence of these currents is greater the worse concrete quality is, and the smaller cover is. The corrosion rate showed differences of almost two orders of magnitude in concrete C30 and of one order of magnitude in concrete C50. When the total corrosion rate is determined only by measuring microcell currents, the obtained values tend to underestimate the mass loss due to corrosion by 90%. Conversely, when the analysis includes macrocell currents, a good fit between the theoretical and real values is obtained.