TAKAHASHI Tsuyoshi
Field Survey and Durability Design of Chloride Affected Bridges on the Coast of Niigata Prefecture
MARUYAMA Kyuichi
The damage by chlorides in concrete structures has been a concerned problem in sea side prefectures of Japan such as Niigata prefecture, and a durability design method toward this problem was firstly specified in the Japanese standard specifications for concrete structures, maintenance in 2001. However, it has been important to validate the actual design method.
In this study, the validity of the actual design method against chlorides attack was evaluated. This was made through the comparison between an evaluation of the deterioration and the results of field survey of the bridges in the coastal area of Niigata prefecture. The total of bridges surveyed was 355 and the 67% bridges were deteriorated by chloride attack. Furthermore, by surveying the service period of bridges and the distance from the coast, it is cleared that the smaller the distance from the coast is, the more serious the deterioration of bridge is. As next step, the results obtained from the field survey and the estimated results from the design method at the present are compared. I found that the current design criteria is secure¡¥
Through the field survey, many deteriorated bridges which have small cover depth were found. Therefore, I measured the distance to rebars from the concrete surface with electromagnetic wave radar. The chloride ions content was estimated from the durability design equations with use of the measured cover depth. It is cleared that the accuracy of deterioration prediction is able to be modified with use of the actual cover depth.
Finally, I conducted a chloride migration analysis using the salt flux as a boundary condition. Numerical result was better than that of conventional design equation.
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