Influence of Condensation due to Temperature Difference on Corrosion Process of Exposed Reinforcement Structure

Abstract

The environment in a reinforced concrete communications manhole is always very humid and exposed steel bar can easily become corroded. However, since the depth below ground of these manholes is relatively shallow and the annual temperature change is modest compared to that for above-ground structures, it is assumed that the factors controlling the progress of steel bar corrosion are different than those for other structures. Moreover, manholes basically represent an isolated environment and there are no additional substances such as sea salt present compared to the outside air. In this relatively static environment, it is thought that the amount of water vapor is the main cause of change in the corrosion rate. Therefore, in this study, in order to clarify the supply mechanism of water that promotes steel bar corrosion in manholes, the relationship among the actual manhole temperature, humidity, and the corrosion rate was investigated. The results show that in winter, the temperature of the manhole ceiling is lower than the dew point temperature, so condensation occurs and steel bar corrosion progresses. Based on repeated temporal experiments, we find that the increase in condensation due to the difference between the dew point temperature and the temperature of the ceiling must be considered in order to explain the steel bar corrosion rate in manholes.