Macrocell Effect on Chloride Threshold Value and Corrosion Rate of Steel Bar in Simulated Concrete Pore Solution

Abstract

In this work, the influence of the area ratio of the low corrosion probability area (prone to becoming cathode) and high corrosion probability area (prone to becoming anode) on the initiation of macrocell corrosion of a steel bar in a simulated pore solution was investigated, along with the depassivation mechanism under the macrocell effect. Meanwhile, the set cathode-to-anode area ratio (SC/A) and the actual cathode-to-anode (pitted) area ratio (SC/A′) after corrosion initiation were compared. The results reveal that the increase in SC/A not only increases the corrosion current density but also promotes corrosion initiation drastically. A pronounced positive shift was observed at high SC/A in the initiation phase due to intensified chloride adsorption and the double-layer effect on the passive film of the anodic steel bar. The chloride threshold value (CTV) could be reduced to 42% of the original time in the simulated concrete pore solution, and the pit depth was increased by up to 124% due to the macrocell effect. In addition, the actual corrosion area (Sact) is much smaller than the set anode area (SA) because the corrosion area created by chloride ions is tiny, resulting in SC/A′ being higher than SC/A.