QuangHo NGUYEN

Modeling the chloride loss process of the concrete surface layer due to rainfall

Takumi SHIMOMURA

In concrete structures in a coastal environment, there is a problem that the safety and durability of the structure is reduced by the arrival and internal penetration of flying salt generated from the sea area and corrosion of the reinforcing bars. Actually, there is a difference in the amount of salt depending on the location of the structure depending on the presence or absence of rainfall. In this study, we have developed a model that clarifies and reproduces the salt loss phenomenon of the concrete surface layer affected by rainfall.
First,the model applies Noyes-Whitney's theory of dissolution to model phenomenon (1), and proposes two phases of gas and liquid that take into account the movement of water vapor driven by the concentration gradient and the movement of liquid water driven by the capillary force. Phenomenon (2) was modeled using the existing gas-liquid two-phase model, and the two models were integrated to construct a model that can reproduce the salt loss phenomenon in a concrete specimen subjected to rainfall action.
Next, the hypothesis established was tested experimentally. In Experiment (1), a mortar specimen containing salt in advance was attached to an experimental model simulating the T-type and flat-type piers, and experiments were conducted by artificial rainfall and natural precipitation. As a result, the amount of salt decreased by 30 to 50% from the position not affected by the precipitation to the position affected by the precipitation. In Experiment (2), a certain amount of salt was supplied and the concrete specimen was subjected to a rainfall experiment by indoor and outdoor experiments. As a result, the total salt content of the concrete specimens subjected to the precipitation effect decreased, and the closer to the surface, the larger the reduced salt content.
Finally, the analysis results and experimental results were compared in order to examine the applicability of the constructed model. The analysis results and the experimental results tended to be similar, and the salt loss phenomenon in the concrete specimen could be reproduced by rainfall.