Non-destructive bond stress evaluation of bending and shear deformed reinforced concrete structure using neutron diffraction

Suzuki, Hiroshi; Kusunoki, Koichi*; Satake, Kosuke*; Kanematsu, Manabu*; Koyama, Taku*; Niwa, Akinobu*; Kabayama, Kenji*; Mukai, Tomohisa*; Kawasaki, Takuro; Harjo, S.

Hihakai Kensa, 67(4), p.180 - 186, 2018/04

https://doi.org/10.11396/jjsndi.67.180

The bond behavior between rebar and concrete under bending moment was investigated by measuring the stress distribution in the two-dimensionally distributed rebars embedded in the reinforced concrete (RC) beam using neutron diffraction. The stress distributions in both of the main rebar and the transverse stirrups embedded in concrete were successfully measured at the fixed measurement configuration without any sample rotations, by suggesting a simple measurement technique on the premise that the transverse restriction from the surrounding concrete to the main rebar is negligible. The bending and shear fracture behavior of the RC beam specimen was predicted by comparing changes in the stress distribution in the rebars measured by neutron diffraction with respect to the applied stress, with the macroscopic deformation measured by strain gauges fixed on the concrete surface. In this study, it was found that the neutron diffraction technique can be a useful technique to evaluate not only the anchorage performance but also the bending behavior of the RC beam.

Propagation behaviour of general and localised corrosion of carbon steel in simulated groundwater under aerobic conditions

Taniguchi, Naoki; Suzuki, Hiroyuki; Kawasaki, Manabu; Naito, Morimasa; Kobayashi, Masato*; Takahashi, Rieko*; Asano, Hidekazu*

Corrosion Engineering, Science and Technology, 46(2), p.117 - 123, 2011/04

https://doi.org/10.1179/1743278210Y.0000000011

Carbon steel has been selected as one of the candidate materials for overpack for geological disposal of high-level radioactive waste in Japan. Corrosion of carbon steel is divided into two types; general corrosion and localized corrosion. In this study, propagation behaviors of general and localized corrosions (pitting corrosion and crevice corrosion) were investigated by immersion tests of carbon steel under aerobic condition. The results of the immersion tests showed that the growth rate of corrosion was strongly dependent on the environmental condition and steel type, but the upper limit of pitting factor (the ratio of the maximum corrosion depth and the average corrosion depth) was approximately determined by only average corrosion depth. Based on these experimental data and literature data, an empirical model that predicts the maximum corrosion depth of an overpack from average corrosion depth was developed by applying the extreme value statistical analysis using the Gumbel distribution function.

Stress corrosion cracking behavior of pure copper in ammonia solution and groundwater containing ammonium ion

Taniguchi, Naoki; Kawasaki, Manabu; Naito, Morimasa

JAEA-Research 2009-067, 29 Pages, 2010/03

JAEA-Research-2009-067.pdf:8.68MB

Since the propagation rate of stress corrosion cracking (SCC) is generally larger than that of other corrosion mode without cracking, it is difficult to avoid the penetration due to SCC by designing the corrosion allowance. Therefore, it is important to clarify the possibility of SCC initiation or conditions where SCC is possible to be occurred. It has been known that copper and copper alloys are susceptible to SCC in ammonia environment depending on the conditions. In this study, the SCC susceptibility of oxygen free copper was investigated in ammonia solution and groundwater containing ammonium ion under oxidizing condition by slow strain rate technique. As the results, no SCC was observed both in 0.05M and 0.1M NHOH solution. In Horonobe groundwater containing ammonium ion, brittle fracture surface and cracks were observed at -144mV vs. SCE. The morphologies of the SCC were not only intergranular type but also transgranular type and transgranular cracks branched from intergranular crack. In these test conditions, corrosion products were strongly adhered to the specimen surface and inside of the cracks. This indicates that the SCC was caused by tarnish rupture mechanism. In buffer material saturated with Horonobe groundwater, mechanical properties such as maximum stress and fracture strain were comparable with those in silicon oil, and no distinct cracks due to SCC were detected on the specimens.

Anodic polarization behavior and film breakdown potential of pure copper in the simulated geological environment containing carbonate

Kawasaki, Manabu; Taniguchi, Naoki; Naito, Morimasa

Zairyo To Kankyo, 58(11), p.386 - 394, 2009/11

https://doi.org/10.3323/jcorr.58.386

In order to clarify the influence of environmental factors on the corrosion behavior of copper overpacks in oxidizing environment, potentiodynamic and potentiostatic anodic polarization tests were performed in carbonate aqueous solutions at 80 C. As the results, the passivation was promoted and film breakdown was suppressed in higher carbonate concentrations, in lower chloride ion concentrations, and in higher pH conditions. The sulfate ion tended to promote the film breakdown of copper. The effects of the composition of the test solutions on the anodic polarization curve of copper in bentonite/sand mixture were quite smaller than those in simple aqueous solution. By comparison with previous data for lower temperature condition, it was clarified that passivation of copper was promoted in higher temperature condition, but breakdown potential, Eb was independent of temperature. The Eb, was expressed as a function of the ratio of aggressive ion and inhibiting ion such as [Cl]/[HCO] and [SO]/[HCO], and it was confirmed that the Eb was lowered with increasing the ratio. When the ratio exceeds a certain value, the Eb was no longer able to be determined since the anodic poralization curve becomes active dissolution type. The lower limit of Eb in passive type region was estimated to be about -200mV vs. SCE. The results of potentiostatic tests showed that pitting corrosion or non-uniform corrosion was observed at the potentials over Eb or second current peak potentials in anodic polarization curve.

Experimental study on corrosion behavior of carbon steel in buffer material, 2; Analysis of corrosion products on coupons immersed for 10 years duration

Taniguchi, Naoki; Kawasaki, Manabu; Naito, Morimasa

JAEA-Research 2008-108, 58 Pages, 2009/02

JAEA-Research-2008-108.pdf:30.01MB

Immersion tests of carbon steel were performed in compacted bentonite simulating the buffer material for 10 years duration, and corrosion products formed on the coupon surface were observed and analyzed by various methods. And then, the stability and dissolution/precipitation behavior of corrosion products were discussed from the view point of thermodynamics. The results of this study are summarized as follows; (1) In the case of the test in 80 C, black or dark gray corrosion product was formed on the coupons, and it was tightly adhered to the surface. By contrast, in lower temperature of 50 C, no tight corrosion product was observed on the coupon surface. (2) Ferrous carbonate corrosion products such as siderite, FeCO or Fe(OH)CO were identified as the crystallized corrosion products in seawater type test solutions. In the test result in dilute test solution, magnetite, (FeO) was identified and no carbonate compounds were found. The presence of these compounds was agreed with thermo dynamical aspects assuming the test conditions. (3) Ca, S, Si and Al were detected in corrosion products layer besides Fe, and their distribution patterns were dependent on the experimental conditions. (4) It was indicated that the corrosion rate of carbon steel in compacted bentonite was correlated to the behavior of dissolution/precipitation of the corrosion products. (5) A conceptual model of the corrosion propagation behavior of carbon steel in compacted bentonite was proposed with reference to the existing corrosion models.

Anodic polarization behavior of pure copper in carbonate solutions

Kawasaki, Manabu*; Taniguchi, Naoki; Naito, Morimasa

JAEA-Research 2008-012, 55 Pages, 2008/03

JAEA-Research-2008-012.pdf:38.56MB

Copper is one of the candidate materials for overpacks. The redox condition at the early stage of the post closure will be oxidizing. In order to understand the influence of environmental factors on the corrosion behavior of copper in such oxidizing environment, anodic polarization tests were performed in carbonate aqueous solution with varying the concentration of representative chemical species in groundwater. As the results of potentiodynamic and potentiostatic tests, anodic polarization behavior of pure copper was summarized as follows; (1) Carbonate ion and bicarbonate ion promoted the passivation of pure copper, and suppressed the initiation of film breakdown. (2) Chloride ion promoted both the active dissolution and initiation of film breakdown of pure copper. (3) The influence of sulfate ion and pH was small, but the action of sulfate ion to the pure copper was similar to that of chloride ion, and the increase of pH was likely to promote the passivation and suppress the initiation of film breakedown. (4) The film breakedown potential, Eb, was represented as a function of the ratio of aggressive ion and inhibiting ion such as [Cl]/[ HCO], [SO]/[HCO]. When the ratio exceeds a certain value, the anodic poralization curve becomes active dissolution type so that no macroscopic film breakedown can not be occured. The lower limit of Eb in passive type region was estimated to be about -200 mV vs. SCE. (5) As the results of potentio static tests, the corrosion form near the Eb was uniform dissolution over the surface, but pitting corrosion and non-uniform corrosion occurred according to the condition of the test solution. Neither pitting corrosion nor non-uniform corrosion occurred at the potential below Eb in every test cases.

Effect of sulfide on the corrosion behavior of pure copper under anaerobic condition and possibility of super long lifetime for copper overpacks

Taniguchi, Naoki; Kawasaki, Manabu*; Naito, Morimasa

JAEA-Research 2007-022, 64 Pages, 2007/03

JAEA-Research-2007-022.pdf:11.4MB

In general, copper is thermodynamically stable under anaerobic condition, so that corrosion due to water reduction can not be occurred on copper. In the presence of sulfide, however, this property of immunity to corrosion is lost and corrosion as copper sulfide is occured. Therefore, it is necessary to understand the effect of sulfide on the corrosion behavior of copper for using the copper as a material for overpacks. In this study, immersion tests and stress corrosion cracking tests were carried out using synthetic seawater containing sodium sulfide. Based on the experimental results, the possibility of super long lifetime for copper overpacks was discussed. The results were summarized as follows; (1) As the results of the immersion tests of copper in buffer material for 2 years, the corrosion rates became large with increase in the concentration of sodium sulfide. The corrosion rates of copper in sodium sulfide of 0.001M, 0.005M and 0.1M were estimated to be 0.55micro-m/y, 2.2micro-m/y, 15micro-m/y respectively. (2) Corrosion product film with black or dark-gray was formed on the surface of copper specimens, and it was identified as CuS(Chalcocite) by the X-ray diffraction. (3) As the results of stress corrosion cracking experiments by means of slow strain rate technique, copper has little susceptibility to crack initiation in the condition of 0.001M-NaS. Obvious cracks were observed in the condition of NaS concentration over 0.005M. (4) According to the results of immersion tests and stress corrosion cracking tests, copper overpacks have a potential to accomplish super long lifetime far over 1000years if the sulfide concentration in repository condition is promised to be less than 0.001M because of very low corrosion rate and no stress corrosion cracking.

Corrosion Assessment of Pure Copper in Synthetic Sea Water Containing Sulfide

Kawasaki, Manabu*; Taniguchi, Naoki; Kawakami, Susumu

JNC TN8400 2004-027, 94 Pages, 2005/03

JNC-TN8400-2004-027.pdf:59.54MB

The immersion tests of pure copper which is one of the candidate overpack materials were carried out in synthetic sea water (SSW) and in bentonite under low oxygen atmosphere at 80 degrees Celsius with changing the sulfide concentration. As the results, corrosion rates became large with increase in sulfide concentration both in simple solution and in bentonite. The corrosion rates tended to be lowered with time in every cases. Assuming that the corrosion is controlled by diffusion of HS- in bentonite, the corrosion rates were calculated for experimental conditions of bentonite thickness and compared with the values obtained in the experiments. The calculated corrosion depths were larger than experimental results. And then assuming the actual thickness of the buffer material, the long-term corrosion depth was estimated based on the diffusion of HS- in bentonite. As the results, the corrosion depth in 1000 years was 0.5mm (HS- 0.001M), 1.76mm (HS- 0.005M), 14mm (HS- 0.1M). It is likely that the corrosion product film formed in solution was tightly adhere to surface and seemed to protective. On the other hand, only a thin film was observed in bentonite at low sulfide concentration condition, and the corrosion product film formed in high sulfide concentration condition was easily broken away from the surface. It is considered that corrosion product formed in bentonite was less protective. According to the X-ray diffraction measurement, Cu2O (cuprite) was detected in SSW without sulfide, and Cu2S (chalcocite) was detected in the presence of sulfide.

Corrosion Rate and Corrosion Localization of Pure Copper in Simulated Groundwater under Aerated Condition

Kawasaki, Manabu*; Taniguchi, Naoki; Kawakami, Susumu

JNC TN8400 2003-041, 48 Pages, 2004/02

JNC-TN8400-2003-041.pdf:0.62MB

Copper is one of the candidate materials for overpacks and it is important to understand the corrosion behavior under oxidizing condition at the initial stage of repository. For understanding the influence of environmental factor on the corrosion rate of copper and corrosion localization, immersion tests of pure copper in aqueous solution and in bentonite were carried out under aerated condition in simulated groundwater environment.As the result, corrosion rate increased with increase in chloride ion concentration and fluoride ion concentration. The addition of bicarbonate ion reduced the corrosion rate of pure copper in the presence of chloride ion. The corrosion rates in bentonite were smaller than those in aqueous solution without bentonite, and decreased with increase in solid- (bentonite)/liquid(solution) ratio. For corrosion localization, the relationship between average corrosion depth and pitting factor was investigated. Although the magnitude of pitting factor depended on the experimental condition, it was tend to decrease with increase in average corrosion depth in all test cases. No data on pitting factor was over the upper limit level observed in natural soils. It was indicated that the maximum corrosion depth due to oxygen can be evaluated conservatively by estimating the upper limit of pitting factor from average corrosion depth.

Propagation Behaviour of Lozalised Corrosion of Carbon Steel in Slightly Alkaline and Alkaline Environment

Taniguchi, Naoki; Kawasaki, Manabu*; Kawakami, Susumu; Suzuki, Haruo*

JNC TN8400 2003-016, 89 Pages, 2003/03

JNC-TN8400-2003-016.pdf:1.29MB

In current repository concept of high-level radioactive disposal in soft rock system, concrete support will be emplaced around the buffer material, and groundwater pH will be increased by the contact with cement. In such condition, carbon steel overpack i