1.

論文(リポジトリ)

論文(リポジトリ)
具志, 幸昌 ; 和仁屋, 晴讙 ; 伊良波, 繁雄 ; Gushi, Yukimasa ; Waniya, Haruyoshi ; Iraha, Shigeo
出版情報: 琉球大学工学部紀要.  pp.35-41,  1980-09.  琉球大学工学部
URL: http://hdl.handle.net/20.500.12000/17688
概要: This is the second report of the results of experiments, named Experiments 6, which aims to determine the threshold values of NaCl concentrations in concrete for steel bar rusting, where corrosion inhibitors exist in concrete. In Experiments 6, there have been small dosages of NaCl in concrete specimens and corrosion inhibitors are also dosed in some specified values. The following results about steel bar rusting are obtained when 12 months have passed after steel bars had been embedded into concrete. 1. There have been found very small rusting spots on one bar at nine and twelve months after embedding, respectively. The bars above are embedded in the concrete of 0.033% NaCl dosage and no corrosion inhibitor. 2. There have been no sign of corrosion on the surface of the bars in the specimens contained 0.033% NaCl and the specified values of corrosion inhibitors. 3. Steel bars in the concrete contained 0.067% of NaCl by weight do not also corroded yet except one bar, where adequate amounts of corrosion inhibitors are added into the concrete. 4. In case of the standard specified dosage of corrosion inhibitors, there have been some amounts of rusting areas on steel bar surfaces embedded in the concrete of 0.100% NaCl concentration, and appreciable amounts of corrosion areas of rusting in the concrete of 0.133% NaCl concentration. The above rusting areas have both increased as the time has passed. 5. Two-fold dosage of corrosion inhibitors in concrete has significant effects on inhibiting corrosion of steel bars in the concrete of 0.100% and 0.133% NaCl concentration, but in that case, emergence of steel bar corrosion itself can not be interrupted. 6. There can be said at the time when one year has passed after embedding steel bars that "threshold" value of NaCl concentration in concrete on rusting of steel bars is 0.067% by weight of concrete where adequate amounts of corrosion inhibitors exists, and that the value can be raised as much as 0.100%. 続きを見る
2.

論文(リポジトリ)

論文(リポジトリ)
具志, 幸昌 ; 和仁屋, 晴讙 ; 伊良波, 繁雄 ; Gushi, Yukimasa ; Waniya, Haruyoshi ; Iraha, Shigeo
出版情報: 琉球大学工学部紀要.  pp.41-46,  1980-03.  琉球大学工学部
URL: http://hdl.handle.net/20.500.12000/17689
概要: The paper is the 2nd report of the 5th series of experiments on corrosion tests of steel bars embedded in concrete specimens. The concrete of specimens in this series of experiments has contained salt and corrosion inhibitors, and its water-cement ratio is 50%. The cover concrete depth over steel bars is constant through all the specimens and 2cm. The experiments has been planned and undertaken in accordance with the L_9 (3^4) Table of the Experimental Design. Salt concentration and dosage of corrosion inhibitor are main factors of the experiments, and their levels are 0.03, 0.15, and 0.75% of concrete by weight in salt concentration and two, three, and four times of the standard dosage of the maker specified in corrosion inhibitor content. The main feature of this series of experiments is high dosage of corrosion inhibitor into concrete to clarify the effect of inhibitor under high salt concentration in concrete. The following results are obtained at the time when one and half year has passed after embedding steel bars into concrets specimens. 1. Two times dosage of the inhibitor has been enough to inhibite corrosion of steel bars in the concrete which contain 0.03 and 0.15% of salt by weight. 2. Where salt content of concrete specimens amounts to as much as 0.75% by weight, the high dosages of inhibitor of this series of experiments could not restrain the rusting of steel bars, and almost steel bars in the specimens of 0.75% salt concentration have had some corrosion. 3. The effect due to differences of dosages of inhibitor are observed where the specimen concrete contain 0.75% salt by weight. The two times dosage of inhibitor is most effective for inhibiting corrosion of steel bars, the three times dosage seemed to have adverse effect on corrosion inhibitation. 4. The interaction of main factor effects between salt concentration in concrete and dosage of inhibitor has been established in this series of experiments, and we could not talk about the effect of inhibitors on corrosion protection without mentioning the salt concentration at the same time. 続きを見る
3.

論文(リポジトリ)

論文(リポジトリ)
具志, 幸昌 ; 和仁屋, 晴讙 ; 伊良波, 繁雄 ; Gushi, Yukimasa ; Waniya, Haruyoshi ; Iraha, Shigeo
出版情報: 琉球大学工学部紀要.  pp.13-40,  1980-03.  琉球大学工学部
URL: http://hdl.handle.net/20.500.12000/17690
概要: 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. 続きを見る