Kazuaki WATANABE

Evaluation of Hydrothermal Condition in Manholes for Information Network and Prediction of Reinforcement Bar Corrosion Based on an Integrated Structural-Ground Heat Transfer Analysis.

Takumi SHIMOMURA

Nowadays, Japan has around 700,000 of communication manholes. It is important to effectively maintain them because 80% of them is estimated to be degraded by 2030. In this research, a deterioration prediction system that can evaluate the risk of corrosion of reinforcement in concrete due to the dew condensation on concrete surface in manhole, was developed and an efficient maintenance plan for communication manholes was proposed.
Firstly, an integrated heat transfer analysis method for ground and manhole, was developed.Then, numerical simulations of occurrence of dew condensation and moisture transfer in concrete manholes were conducted, and water content in concrete was calculated. Through comparison of computations and measurements results, it was confirmed that the surface temperature of concrete and internal temperature of manholes in various regions of Japan can be accurately simulated. Analytical results showed that concrete in manholes are saturated during winter and dried in summer and that this tendency repeats annually with gradual change.
In addition, experimental works were conducted to model the effects of water in concrete on corrosion of reinforcement steel. Experimental specimens of reinforced concrete(RC) and reinforcement bar were prepared, and their corrosion process under various actions of water as well as the natural potential was observed. As experimental results, great degree of corrosion  was observed under a relative humidity of 100% and underwater environments.
Furthermore, based on the moisture condition of the manholes and the experimental results, a deterioration prediction system, was developed. As analytical results, it was demonstrated that calculations can generally simulate rebar corrosion before the occurrence of spalling of concrete cover inside of manholes of Japan. In addition, various maintenance scenarios of communication manhole were proposed and its respective costs were compared. In addition, based on prediction methods of manholes deterioration, it was shown that the maintenance costs can be drastically reduced when manholes are repaired before spalling of concrete occurs.