コンクリート中の鉄筋の発錆実験　その6　－実験6　塩分量が少ない場合、その1－

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This is the first report of the results of the series of experiments which have been carried on by the authors from December 1978 to February 1979. This series of experiments, named Experiments 6, aimed to determine the threshold values of NaCl concentrations in concrete for steel bar rusting. A method of electrical potential difference measurements of spots of concrete specimen surfaces over Cu/CuSO_4 half cell, having been developed by California Division of Highways and having been widely used to detect the rusting spots of steel bars in concrete, are also performed in this series of experiments. We planned to examine the method, if it can be applicable to the RC structures in Okinawa Prefecture to detect rusting spots. The following results about steel bar corrosion are obtained by and at six months after embedding steel bars in concrete. 1. Steel bars in the concrete contained 0.033% of NaCl have not corroded yet without adding any amount of corrosion inhibitors. 2. Steel bars in the concrete contained 0.067% of NaCl do not also corrode yet, if adequate amount of corrosion inhibitors are added to the concrete. 3. In case of the concrete contained 0.100% of NaCl by weight, there have been steel bars corroded some, but their areas of corrosion were small. Some of the steel bars have no corrosion spots where adequate amount of corrosion inhibitors had added to the concrete. 4. All steel bars in the concrete contained 0.133% of NaCl by weight except A_4 D_2 C_2 O_1 specimens have been observed some corrosion. And as the time has passed, the areas of corrosion on steel bar surfaces are becoming larger. 5. There have not been any significant differences in the effects of types of corrosion inhibitors on steel bar corrosion. 6. The effects of water-cement ratio on corrosion of steel bars are not obvious. 7. The beneficial effects of doubled dosage of corrosion inhibitors into concrete are observed on steel bar corrosion. The results of electrical potential measurments on the basis of Cu/CuSO_4 half cell are as follows. 1. It has not been decided yet that the standards of California Division of Highways on steel bar corrosion in concrete can be applicable to the RC structures in Okinawa Prefecture. 2. Steel bars in concrete need not be connected by metalic means each other when half cell potential measurment method is applied. 3. Rusting spots on steel bar surfaces have high potentials, and the electrical circuit directly contained a rusting spot exhibit high potentials in the sense of absolute value. 4. Almost rusting places have occured in the underside of steel bars, and the underside of the specimen has considerable larger cover depth over steel bars than the upperside. The electrical potentials measured on the underside of a specimen were always higher than on upperside. 5. Moisture condition of the specimen concrete has strong effect on measured potential values. 6. There have been no corrosion on the steel bars in the specimens which exhibit 0.2 volt or less of electrical potential. 7. There have been very few specimens which exhibit the electrical potential value of 0.3 volt or higher. 8. The almost specimens having corroded steel bars at 3 or 6 months after embedding exhibit 0.20 to 0.30 volt higher on the basis of Cu/CuSO_4 half cell.

コンクリート中の鉄筋の発錆実験　その6　－実験6　塩分量が少ない場合、その1－

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コンクリート中の鉄筋の発錆実験 その6 －実験6 塩分量が少ない場合、その1－

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コンクリート中の鉄筋の発錆実験　その6　－実験6　塩分量が少ない場合、その1－