Accelerated Concrete Carbonation and Resulting Rebar Corrosion Under a High Temperature Condition in Nuclear Power Plants

To assess the durability of concrete structures at nuclear power plants in Japan, plant life management technical evaluation is performed in accordance with the guidelines of the Architectural Institute of Japan for the maintenance and management of structures in nuclear facilities. Concrete carbonation is one of the degradation factors covered in the guidelines, and sampling is performed to confirm the progression of carbonation and predict future progression. Electricity providers in Japan perform sampling at locations constituting environments (temperature, relative humidity, carbon dioxide concentration) where carbonation progresses relatively fast to confirm that carbonation has not reached the rebars and to predict progression. In this study, accelerated carbonation tests were performed at high temperature, which is believed to accelerate carbonation, considering the parameters of relative humidity. Progression of carbonation and its impact on rebar corrosion were examined. The results showed that progression of carbonation in high-temperature environments can be predicted with a margin of safety using the Architectural Institute of Japan’s durability prediction equation. Moreover, because the humidity environments where carbonation progresses and the temperature environments where rebar corrosion progresses do not correspond with each other, rebars are typically unlikely to corrode even if carbonation has reached the rebars, provided they are not subjected to extreme wet-dry cycles.