1.

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論文(リポジトリ)
伊良波, 繁雄 ; 具志, 幸昌 ; 和仁屋, 晴讙 ; Iraha, Shigeo ; Gushi, Yukimasa ; Waniya, Haruyoshi
出版情報: 琉球大学工学部紀要.  pp.59-69,  1982-09.  琉球大学工学部
URL: http://hdl.handle.net/20.500.12000/17671
概要: Bond failure of deformed reinforcing bars generally takes place by splitting of surrounding cover concrete, unless they are confined by heavy reinforcements in surrounding. Therefore. bond strength of deformed reinforcing bars is determined by the cracking resistance of cover concrete. This paper presents analytical method the determine cracking strength of cover concrete by the finite element method where only the effect of tensile cracking is considered to simplify the failure structure of the model. The following results are obtained. 1. Progressive behavior of cracking and cracking strength of cover concrete are determined. 2. Radial stresses perpendicular to the surface of reinforcing bars are uniform before cracks start in concrete and become non-uniform after cracks develop.
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2.

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和仁屋, 晴讙 ; 具志, 幸昌 ; 伊良波, 繁雄 ; Waniya, Haruyoshi ; Gushi, Yukimasa ; Iraha, Shigeo
出版情報: 琉球大学工学部紀要.  pp.47-57,  1982-09.  琉球大学工学部
URL: http://hdl.handle.net/20.500.12000/17672
概要: This paper presents the effects of corrosion on bond behavior of reinforcing bars. Pull-out and push-out tests were perf ormed for specimens of 15cm cube with a deformed bar D19 at the center where the bar was electrolytically corroded before the tests. The bond characteristics of specimens with corroded and non-corroded bars are investigated from the test results. The following results are obtained from the test. 1. Initial surface cracks started when the cumulative current of 5 to 8 amp. hrs. was observed and the width ranged from 0 to 0.20mm. 2. Failure pattern of all specimens was splitting failure. 3. Total slip up to failure at free end with an electrolytically corroded bar was 1/5 to 1/10 times the one with a non-corroded bars. Existence of surface cracks due to corrosion of the bar has no effect on the slip. 4. As for the specimens with cumulative current of less than 5 amp. hrs. when no cracks was observed, the bond strength of electrolytically corroded bars (σ_) was equal to or grater than one of non-corroded (σ_). 5. The value of σ_ / σ_ dropped to 0.50 for the specimens with relatively small cracks showing cumulative current less than 8 amp. hrs. and scattered in the range of 0.25 to 0.50 for the ones having maximum crack width of 0.20 to 0.60mm where cumulative current of 9 to 17 amp. hrs. was observed. It seems that the variance of these values was caused by the existence of defferent internal cracks. 6. For the specimens reinforced with a spiral bar around the center main bar where cracks obsereved, there was no reduction in bond strength and ductile capacity in bond. It is concluded that the reinforcement with a spiral bar around the center contributed beneficially on splitting bond failure.
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3.

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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.35-45,  1982-09.  琉球大学工学部
URL: http://hdl.handle.net/20.500.12000/17687
概要: Investigations have revealed that the damages due to corrosion of Re-bars in RC structures have been prevailing in Okina wa Prefecture and that the major cause of the damages is salt contained in concrete. There has been also disclosed that high values of salt concentration are found much frequently in concrete of RC structures mentioned above. The writers have started a series of experiments to disclose the causality between many causes and their effects on the above high values of salt concentration. The main one among the many causes is considered to be salt intrusion through concrete surface and water movement in concrete due to evaporation. Specimens were placed on some various places under different environments. One year has passed and the following results are obtained. 1. Specimens at coast have been intruded by a large amount of salt during one year period. The amount of 0.4 to 0.8 % salt by weight of mortar in concrete have been found. The effect of initial salt conent on salt concentration has been disappeared after one year. In some specimens at the point 500 m from coast, there have been also observed small increases of salt content in concrete. 2. The influence of W/C on salt concentration by penetration has been also founded in the specimens at coast. The smaller W/C is. the smaller quantities of salt are penetrated at the time one year has passed. The specimens at the point 500 m from coast have also shown the same tendency, but, only the specimen of W/C=70% has indicated a small increase in salt content. At coast, the differences among the quantities of intruded salt are relatively small and the quantities themselves are quite large. The structures at or near sea coast must be taken by some protective measures other than lowering W/C. 3. Coatings on concrete surfaces have some beneficial effects on salt penetration resistance, but there have been a large amount of penetrating salt in concrete of the specimens at coat. The lining of acril-gum coating material has been proved to have an excellent effect on preventing the intrusion of salt into concrete. 4. In all specimens, increases of salt concentration near the surfaces of concrete are observed at the biginning of this experiment. The movement of water toward surfaces in concrete specimens due to drying and evaporation is most responsible for this phenomenon. This phenomenon is termed "Edge effect". The salt concentration near surface amounts to 1.4 to 4 times the one of inside middle part of specimens.
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4.

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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 valu es 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%.
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5.

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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 speci mens. 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.
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6.

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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 Dece mber 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.
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7.

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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 / 和仁屋, 晴讙 ; Iraha, Shigeo
出版情報: 琉球大学理工学部紀要. 工学篇 — Bulletin of Science & Engineering Division, University of the Ryukyus. Engineering.  pp.23-47,  1979-03-01.  琉球大学理工学部 — Science and Engineering Division, University of the Ryukyus
URL: http://hdl.handle.net/20.500.12000/27594
概要: A series of experiments on corrosion of steel bars embedded in concrete has been done at the laboratory of concrete engi neering of University of the Ryukyus. This is the third report of the above experiments and describes the corrosson behavior of steel in concrete at the times of 1.5 year and 2 years after embedding. This series of experiments consists of two parts. One is a study on steel corrosion in the concrete containning none to highly concentrated salt and containning it before and after hardened. The other is a case of study of the influences of the kinds and dosages of corrosion inhibitors and the effect of heating. This third report describes only the former, that is called "Experiment I". Experiment I is divided into two which consist of 16 experiments respectively. The first part of Experiment I is the case of salt dosed before hardening and contained none to high concentration. The second part is the case of slowly penetrating of salt into concrete after hardening. The experiments were planned after so called "Eperimental Design". The following articles are clarified at the times of 1.5 year and two years after embedded. (1) The first part of experiment I. a) The influence of salt contained on the corrosion of steel is still overwhelmingly strong, but it seems the effect is slightly weaken. b) A new tendency emerged that the influence of cover depth of concrete becomes distinctively stronger, because of cracking along steel bars in the test prisms which had thin concrete covers. c) There has been no corrosion detected over the steel surfaces in the concrete which has the water cement ratio of 40% and contained both 0.1% salt and twice the standard dosage of inhibitor. d) At the time of one year, maximum corroded area of steel surfaces was happened in the test prism of concrete contained 0.5% salt concentration, but the steel bars in the concrete contained 1% salt concentration have become mostly corroded at the times of 1.5 year and 2 years. e) The sudden increases of corroded areas of steel bars are found in the test prisms of thiner concrete covers and lareger water cement ratios. f) The highly inhibiting ability of the concrete of the water cement ratio of 40% has been demonstrated, but the considerable quantities of corrosion of steel bars can not be avoided in that concrete when the salt concentration becomes high. (2) The second part of Experiment I. a) The effect of salt on corrosion of steel bars has become stronger in the second part. b) The "sprayed" and "half-immersed" test prisms have increased the corroded areas of steel bars as the progress of time, but the "completely immersed" and "natural" test prisms appeared no sign of increasing of corrosion areas. c) The concrete of water cement ratio of 40% has strong corrosion inhibiting ability. At the time of two years passed, the steel bars in that concrete have not corroded yet in the second part of experiment I. d) The corrosion inhibiting agent used in this study has good inhibiting ability, but can not be stopped to corrode when the salt concentration of concnete becomes higher as the time has passed.
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8.

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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.53-59,  1979-11.  琉球大学工学部
URL: http://hdl.handle.net/20.500.12000/17707
概要: There has been said that the more salt in concrete needs the more dosage of inhibitors in concrete to prevent steels fro m corrosion. In Okinawa Prefectures, the reinforced concrete structures contain too much quantity of salt in their body concrete, and the serious damages of the structures due to steel corrosion have been prevailing overall the Prefecture. In this series of experiments, over-dosed corrosion inhibitor is contained in concrete to prevent steels from rusting. The experimental factors are salt content and dosage of inhibitor in concrete, and the levels of the former are 0.05, 0.15 and 0.75% of salt by weight of concrete and the levels of latter are two, three and four times as much as standard dosage of inhibitor which the makers specify. The experiments have been done in accordance with so-called "Experimental Design". The two-times-dosage of inhibitor is quite enough to inhibite the corrosion of steels in the concrete containing salt as much as 0.75% by weight. Three-and four-times-dosages are sufficient for preventing steels in the concrete containing as much as 0.15% salt from rusting. But the dosages couldn't inhibite the corrosion of steels in the concrete with 0.75% salt contained. This result seems to be quite strange, but it is concluded as in Experiments 1 that "when there are contained much salt (for instance, over 0.50% by weight of concrete in experiments 1), the more inhibitor exists, the more corrosion of steels results". Up to 9 month after embedding steels in concrete, an two-times-dosage of inhibitor seems to be quite enough for preventing steels in the concrete with 0.75% salt from rusting. The water cement ratio of 50 % may contribute to the above result.
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9.

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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.37-51,  1979-11.  琉球大学工学部
URL: http://hdl.handle.net/20.500.12000/17708
概要: This is the 4th report of the series of experiments which the authors have been undertaken on the subject of steel corro sion in concrete. The test results and their investigations at one and half year and two years after embedding the steels in concrete are described. This series of experiments consists of nine experiments on accordance with L_9(3^4) Table of "Experimental Design". Salt contents in concrete, types of corrosion inhibitors and dosages of inhibitors are main factors in the experiments. All the factors have three levels, heating the specimens or not is also a main factor in the experiments. The following facts are clarified in the study. (1) Heating the specimens at 50℃ for one hour and sinking them into water for two hours per day have an accelarating effect on corrosion of steels in concrete. (2) The effect of types of inhibitors on corrosion of steels is not so clear, if any, the total areas of corrosion due to the difference of types are becoming equalized as the time has passed. (3) The influence of salt contents in concrete on corrosion of steel has been overwhelmingly strong, it results in that the more salt content in concrete bring about the more corrosive areas on steel surface. (4) The influence of dosages of inhibitors couldn't be appreciated because of interaction between the salt content and the dosage of inhibitor. So, the corrosion preventing effect of inhibitor must be mentioned in connection with salt content. (5) The cracks on concrete surfaces due to steel corrosion have become strong effect on the rate of steel corrosion at the time when two years have passed after embedding.
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10.

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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.25-36,  1979-11.  琉球大学工学部
URL: http://hdl.handle.net/20.500.12000/17709
概要: The authors have performed a series of experiments on corrosion behavior of steel bars embedded in concrete. In these ex periments many types of corrosion inhibitors and a variety of quantities of salt were added to concrete. The chemicals seemed to have influences on the physical behaviors and compressive strength of concrete. Although the measurements of strength and physical properties of concrete were not intended in these experiments and results obtained on those items were secondary minors, the authors have had much materials about them. So, some of them are to be described in the following. (1) Favorable effects of using commercial-made corrosion inhibitors on concrete strength were observed in the experiments. (2) The effects of salt contents in concrete on the 28th-day concrete strength were somewhat complex phenomenon. On the average adding salt into concrete caused a little lower strengths, there observed the minimum strength at the concentration of NaCl in concrete between 0.03% and 0.15%, then increasing tendency of strength could be seen until salt content increased to 0.25% which corresponded to the concentration of NaCl in sea-water mixing concrete. Thereafter the more NaCl concentration in the concrete, lower the strength ensured. (3) The effect of salt dosage in concrete mixing on slump value was small. But tendency that larger concentration caused less slump was observed. (4) The influence of the types of corrosion inhibitors on slump value was not significant in the analysis of variance except the one containing water-reducing agent. (5) It was found that water-cement ratio had most significant effect on slump value except the effect of unit water in concrete. (6) The less bleeding water was brought about as salt dosage become larger. But the salt content not more than the one resulted from using the ordinary sea-sand would not so much effective. (7) Some types of corrosion inhibitors seemed to be effective on bleeding behavior of concrete. (8) On the dosage of salt in concrete or cement paste, the accelerating effect on setting could be observed. (9) Most of the inhibitors used in the experiments had some compensating effects for the above of salt dosage.
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