• Title/Summary/Keyword: time to corrosion initiation

Search Result 82, Processing Time 0.024 seconds

Effect of pre-treatment in 0.5 M oxalic acid containing various NH4F concentrations on PEO Film Formation of AZ91 Mg Alloy (NH4F가 첨가된 0.5 M 옥살산 전처리가 AZ91 마그네슘 합금의 PEO 피막 형성에 미치는 영향)

  • Kwon, Duyoung;Song, Pung-Keun;Moon, Sungmo
    • Journal of the Korean institute of surface engineering
    • /
    • v.55 no.1
    • /
    • pp.24-31
    • /
    • 2022
  • This study investigated the effect of pre-treatment on the PEO film formation of AZ91 Mg alloy. The pre-treatment was conducted for 10 min at room temperature in 0.5 M oxalic acid (C2H2O4) solution containing various ammonium fluoride (NH4F) concentrations. The pre-treated AZ91 Mg specimens were anodized at 100 mA/cm2 of 300 Hz AC for 2 min in 0.1 M NaOH + 0.4 M Na2SiO3 solution. When AZ91 Mg alloy was pretreated in 0.5 M oxalic acid with NH4F concentration less than 0.3 M, continuous dissolution of the AZ91 Mg alloy occurred together with the formation of black smuts and arc initiation time for PEO film formation was very late. It was noticed that corrosion rate of the AZ91 Mg alloy became faster if small amount of NH4F concentration, 0.1 M, is added. The fast corrosion is attributable to fast formation of porous fluoride together with porous oxides in the reaction products. On the other hand, when AZ91 Mg alloy was pretreated in 0.5 M oxalic acid with sufficient NH4F more than 0.3 M, a thin and dense protective film was formed on the AZ91 Mg alloy surface which resulted in faster initiation of arcs and formation of PEO film.

Lifetime Reliability Based Life-Cycle Cost-Effective Optimum Design of Steel Bridges (생애 신뢰성에 기초한 강교의 LCC최적설계)

  • Lee, Kwang Min;Cho, Hyo Nam;Cha, CheolJun;Kim, Seong Hun
    • KSCE Journal of Civil and Environmental Engineering Research
    • /
    • v.26 no.1A
    • /
    • pp.75-89
    • /
    • 2006
  • This paper presents a practical and realistic Life-Cycle Cost (LCC) optimum design methodology of steel bridges considering time effect of bridge reliability under environmental stressors such as corrosion and heavy truck traffics. The LCC functions considered in the LCC optimization consist of initial cost, expected life-cycle maintenance cost and expected life-cycle rehabilitation costs including repair/replacement costs, loss of contents or fatality and injury losses, road user costs, and indirect socio-economic losses. For the assessment of the life-cycle rehabilitation costs, the annual probability of failure which depends upon the prior and updated load and resistance histories should be accounted for. For the purpose, Nowak live load model and a modified corrosion propagation model considering corrosion initiation, corrosion rate, and repainting effect are adopted in this study. The proposed methodology is applied to the LCC optimum design problem of an actual steel box girder bridge with 3 continuous spans (40 m+50 m+40 m=130 m), and various sensitivity analyses of types of steel, local corrosion environments, average daily traffic volume, and discount rates are performed to investigate the effects of various design parameters and conditions on the LCC-effectiveness. From the numerical investigation, it has been observed that local corrosion environments and the number of truck traffics significantly influence the LCC-effective optimum design of steel bridges, and thus realized that these conditions should be considered as crucial parameters for the optimum LCC-effective design.

Estimation of Critical Chloride Content for Corrosion of Reinforcing Steel in Concrete by Field Exposure Experiment (현장 폭로실험에 의한 콘크리트 중 철근의 부식 임계 염화물량 평가)

  • Yu, Kyung-Geun;Bae, Su-Ho;Park, Jae-Im;Lee, Kwang-Myong;Kim, Jee-Sang
    • Proceedings of the Korea Concrete Institute Conference
    • /
    • 2008.04a
    • /
    • pp.585-588
    • /
    • 2008
  • To predict the service life of reinforced concrete structures exposed to chloride environment, quantitative measures of material properties such as the critical chloride content for corrosion in concrete and the diffusion coefficient of chloride ions of concrete and the surface chloride content of the concrete are essential. However, it should be noted that they are influenced by several factors such as concrete mix proportions, cement type, and environmental conditions, etc. Thus, the purpose of this research is to estimate more actually the critical chloride content for corrosion of the reinforcing steel in concrete by field exposure experiment. For this purpose, the prism concrete test specimens were made for water-cement(W/C) ratios of 31%, 42%, 50%, and 70%, and then the field exposure experiment for them were conducted at Youngduk of the east coast for about 3 years. During the test, corrosion monitoring by half cell potential method was carried out to detect the time to initiation of corrosion for test specimens and its chloride content was evaluated by breaking the concrete test specimens when corrosion of the reinforcing steel in concrete was perceived. It was observed from the test results that the critical chloride content for corrosion of reinforcing steel in concrete would be dependent on W/C ratio and almost irrespective of concrete cover.

  • PDF

Variation of Critical Chloride Content of Rebar Embedded in Concrete with Admixture (혼화재 혼입에 따른 콘크리트에 매립된 철근의 부식 임계 염화물량의 변화)

  • Park, Jang-Hyun;Lee, Yun-Su;Lee, Han-Seung
    • Journal of the Korea Institute of Building Construction
    • /
    • v.19 no.6
    • /
    • pp.511-520
    • /
    • 2019
  • The critical chloride content of rebar embedded in concrete was experimentally evaluated according to the admixture replacement ratio and admixture type. Four types of reinforced concrete were mixed OPC 100%, OPC 70% + GGBFS 30%, OPC 40% + GGBFS 60%, and OPC 40% + GGBFS 40% + FA 20%. NaCl solution was supplied to the specimens, and the open circuit potential of the embedded rebar was monitored. The specimens determined to initiate corrosion were cut at intervals of 5mm from the NaCl solution supply surface and conducted to chlorine ion profile. Corrosion initiation time of rebar embedded in concrete was delayed as the admixture replacement ratio increased. Looking at the critical chloride content of the types of reinforced concrete, it was highest in OPC 1.46kg/㎥, followed in order by S30 0.98kg/㎥, TBC 0.74kg/㎥, and S60 0.71kg/㎥.

Effect of Wet Curing Duration on Long-Term Performance of Concrete in Tidal Zone of Marine Environment

  • Khanzadeh-Moradllo, Mehdi;Meshkini, Mohammad H.;Eslamdoost, Ehsan;Sadati, Seyedhamed;Shekarchi, Mohammad
    • International Journal of Concrete Structures and Materials
    • /
    • v.9 no.4
    • /
    • pp.487-498
    • /
    • 2015
  • A proper initial curing is a very simple and inexpensive alternative to improve concrete cover quality and accordingly extend the service life of reinforced concrete structures exposed to aggressive species. A current study investigates the effect of wet curing duration on chloride penetration in plain and blended cement concretes which subjected to tidal exposure condition in south of Iran for 5 years. The results show that wet curing extension preserves concrete against high rate of chloride penetration at early ages and decreases the difference between initial and long-term diffusion coefficients due to improvement of concrete cover quality. But, as the length of exposure period to marine environment increased the effects of initial wet curing became less pronounced. Furthermore, a relationship is developed between wet curing time and diffusion coefficient at early ages and the effect of curing length on time-to-corrosion initiation of concrete is addressed.

Life-Cycle Cost-Effective Optimum Design of Steel Bridges Considering Environmental Stressors (환경영향인자를 고려한 강교의 생애주기비용 최적설계)

  • Lee, Kwang Min;Cho, Hyo Nam;Cha, Cheol Jun
    • Journal of Korean Society of Steel Construction
    • /
    • v.17 no.2 s.75
    • /
    • pp.227-241
    • /
    • 2005
  • This paper presents a practical and realistic Life-Cycle Cost (LCC) optimum design methodology for steel bridges considering the long-term effect of environmental stressors such as corrosion and heavy truck traffics on bridge reliability. The LCC functions considered in the LCC optimization consist of initial cost, expected life-cycle maintenance cost, and expected life-cycle rehabilitation costs including repair/replacement costs, loss of contents or fatality and injury losses, road user costs, and indirect socio-economic losses. For the assessment of the life-cycle rehabilitation costs, the annual probability of failure, which depends upon the prior and updated load and resistance histories, should be accounted for. For the purpose, Nowak live load model and a modified corrosion propagation model, which takes into consideration corrosion initiation, corrosion rate, and repainting effect, are adopted in this study. The proposed methodology is applied to the LCC optimum design problem of an actual steel box girder bridge with 3 continuous spans (40m+50m+40m=130m). Various sensitivity analyses are performed to investigate the effects of various design parameters and conditions on the LCC-effectiveness. From the numerical investigation, it has been observed that local corrosion environments and the volume of truck traffic significantly influence the LCC-effective optimum design of steel bridges. Thus, these conditions should be considered as crucial parameters for the optimum LCC-effective design.

Influence of Chloride Content of on Electrical Resistivity in Concrete (콘크리트내 염소이온량이 전기저항에 미치는 영향)

  • Yoon, In-Seok;Nam, Jin-Won
    • Journal of the Korea institute for structural maintenance and inspection
    • /
    • v.18 no.6
    • /
    • pp.90-96
    • /
    • 2014
  • The electrical resistivity of concrete can be related to two processes involved in corrosion of reinforcement: initiation (chloride penetration) and propagation (corrosion rate). The resisistivity of concrete structure exposed to chloride indicates the risk of early corrosion damage, because a low resistivity is related to rapid chloride penetration and to high corrosion rate. Concrete resistivity is a geometry-independent material property that describes the electrical resistance, which is the ratio between applied voltage and resulting current in a unit cell. In previous study, it was realized that the resistivity of concrete depended on the moisture content in the concrete, microstructural properties, and environmental attack such as carbonation. The current is carried by ions dissolved in the pore liquid. While some data exist on the relationship between moisture content on electrical resistivity of concrete, very little research has been conducted to evaluate the effect of chloride on the conduction of electricity through concrete. The purpose of this study is to examine and quantify the effect of chloride content on surface electrical resistivity measurement of concrete. It was obvious that chloride content had influenced the resistivity of concrete and the relationship showed a linear function. That is, concrete with chloride ions had a comparatively lower resistivity. Decreasing rate of resistivity of concrete was clear at early time, however, after 50 days resistivity was constant irrespective of chloride concentration. Conclusively, this paper suggested the quantitive solution to depict the electrical resistivity of concrete with chloride content.

A performance-based design method for chloride-induced cover cracking of RC structures

  • Yang, Dong-Hui;Yi, Ting-Hua;Li, Hong-Nan
    • Computers and Concrete
    • /
    • v.20 no.5
    • /
    • pp.573-582
    • /
    • 2017
  • Chloride-induced cover cracking will aggravate the performance deterioration for RC structures under the chlorideladen environment, which may endanger the safety of structures and occupants. Traditional design method cannot ensure that a definite performance is satisfied. To overcome the defects, a study on the performance-based design method was carried out in this paper. Firstly, the limit state functions were established for the corrosion initiation and cover cracking. Thereafter, the uncertainty analysis was performed to study the effects of random factors on the time-dependent performances. Partial factor formulae were deduced through the first-order reliability method for performance verification. Finally, an illustrative example was presented and the sensitivity of cover depth to other parameters was carried out. It is found that the uncertainties of the random variables have great effects on the required cover depth. It is demonstrated that the performance-based design method can ensure that the target performance can be satisfied and support to formulate a rational maintenance and repair strategy for RC structures under the chloride environment.

Plugging and Re-opening Phenomena of the 5Cr-1Mo Steel Leak Hole by Water Leakage in Sodium Atmosphere (소듐 분위기에서 물누출에 의한 5Cr-1Mo Ferrite강 구멍의 막힘과 재개방 현상)

  • Jeong, Kyung-Chai;Kim, Tae-Joon;Choi, Jong-Hyeun;Park, Jin-Ho;Hwang, Sung-Tai
    • Applied Chemistry for Engineering
    • /
    • v.9 no.5
    • /
    • pp.674-679
    • /
    • 1998
  • Small water leak experiment was carried out in liquid sodium atmosphere using a specimen of ferrite steel, which will be expected to be a material of the heat transfer tube of liquid metal fast breeder reactor. Self-plugging phenomena of leak path could be explained by the products of reaction and corrosion by sodium-water reaction. Also, re-opening mechanism of self-plugged path could be explained by the thermal transient and vibration of heat transfer tube. As a result, perfect re-opening time of self-plugged leak path was observed to be 129 minutes after water leak initiation. Re-opening shape of a specimen was appeared with double layer of circular type, and re-opening size of this specimen surface was about 2 mm diameter on sodium side.

  • PDF

A Study on the Stress Corrosion Cracking Propagation Behaviors of high Strength Steel by Means of Emission Test (음향방출시험에 의한 고장력강의 응력부식 균열전파 거동에 관한 연구)

  • Yu, Hyo-Seon;Jeong, Se-Hui
    • Korean Journal of Materials Research
    • /
    • v.3 no.4
    • /
    • pp.361-371
    • /
    • 1993
  • Among the various test methods for stress corrusiun cracking(SCC) susceptibility evaluatiun, the slow stram rate test(SSHT) method is a rapid and effective nwthod to evaluate the SCC susceptibility of metal in relatively short time. But it is very difficult to analyze the microfracture behaviors in SCC process by using the test(SSRT) method only. Up to now, it has been well known that the acoustic emission(AE) test is the effective technique to monitor the microcrack initiation and propagation in material fracture pmcess. Therefore. in this paper, we analyzed the correlation between the see process and the characteristics of AE signal by using the SSHT and the AE test. According to the test results. the AE signals produced from the material microfracture were clearly depended on the test environment. The AE signal characteristics generated during see process in synthetic sea water were comparatively greater than those. in air. In addition, the SCC behaviors could be definitely evaluated by the amplitude parameter of AE signals.

  • PDF