• Journal of the Korea Concrete Institute
• /
• v.20 no.6
• /
• pp.671-679
• /
• 2008

The near surface mounted (NSM) FRP strengthening method has been conventionally applied for strengthening the deteriorated concrete structures. The NSM strengthening method, however, has been issued with the problem of limitation of the cutting depth which is usually considered as concrete cover depth. This may be related with degradation of bonding performance in long-term service state. To improve the debonding problem, in this study, the Stirrup partial-cutting NSM (SCNSM) strengthening method using CFRP plate was newly developed. SCNSM strengthening method can be effectively applied to the deteriorated concrete structure without any troubles of insufficient cutting depth. To experimentally verify the structural behavior, the flexural test of the concrete beam by using the SCNSM strengthening method was conducted with the test variable as the strengthening length (32%, 48%, 70%, 80%, 96% of span length). In the result of the test, the NSM and SCNSM strengthened specimen showed similar structural behavior with load-deflection, mode of failure. Additionally, there was no apparent structural degradation by the stirrup partial-cutting. Consequently, it was evaluated that the SCNSM strengthening method can be useful for seriously damaged concrete structures that is hard to apply the conventional NSM strengthening method for increasing the structural capacity.

• Proceedings of the Korean Institute of Surface Engineering Conference
• /
• 2017.05a
• /
• pp.164-164
• /
• 2017

해양환경 중 많이 사용되는 철강재료들은 그 가혹한 부식환경에 대응하기 위하여 일반적으로 피복 도장방식법이나 음극방식법이 적용되고 있다. 여기서 음극방식법은 선박 및 해양구조물의 해중부 부식에 대해 가장 효과적인 방식법으로 알려져 있다. 한편, 이와 같이 해수 중 철강재에 음극방식을 적용할 경우, 피방식체인 그 강재 표면에 해수 중 용존된 산소의 음극환원 반응이 일어나며 국부적인 알카리 표면 조건을 형성시켜 $Mg(OH)_2$와 $CaCO_3$의 막을 석출시킨다. 이와같이 음극방식 중 형성된 전착물은 방식해야 될 표면적을 감소시켜 방식전류밀도를 감소시키는 효과가 있는 것으로 보고되고 있다. 이렇게 석출된 전착물은 음극표면에 부분적으로 형성되고, 여러 가지 환경 조건 등의 영향을 받아 그 피막의 형성 정도도 가늠하기 어렵기 때문에 음극방식 설계 시 그 정도에 따른 영향을 고려-반영하기가 곤란하다. 또한 이 전착물은 그 형성 메커니즘에 관한 해석이나 강도, 균일한 밀착성, 장기적인 방식효과 및 효율성 등이 아직 충분히 입증되어 있지 않은 실정에 있다. 따라서 본 연구에서는 해수 중 다양한 전착 프로세스에 의해 제작된 전착물의 기간별, 도장코팅 종류별 특성변화를 분석 및 평가하고, 전착물에 의한 희생양극 소모전류 변화 측정 분석을 통해 전착막을 균일하고 치밀하게 형성시키기 위한 최적의 조건을 찾고자 하였다. 또한 석출속도, 밀착성 및 내식특성을 향상시키기 위해 해수 중 기체를 용해시켜 제작한 막의 특성을 분석-평가하였다. 본 연구에 사용된 강 기판은 일반구조용강(KS D 3503, SS400)으로 ${\varnothing}42.7{\times}1,000mm{\times}4.0t$의 형상으로 제작하였다. 인가된 전류밀도는 1, 3 및 $5A/m^2$이고 도장 코팅 종류별 전착 석출물의 형성차이 비교 분석을 위한 실험은 선박 및 해양구조물에 많이 사용되는 Universal Epoxy 도료 2종을 선정하여 진행하였다. 또한 Steel Wire Mesh의 영향을 알아보기 위해 Mesh를 설치하여 실험을 진행하였다. 기간별-도장 종류별 외관관찰, 전착물의 두께 측정, SEM, EDS 및 XRD를 통해 막의 모폴로지, 조성원소 및 결정구조를 분석하였으며, 전착물의 내식성과 내구성을 평가하기 위해 테이핑 테스트(Taping Test) 및 전기화학적 양극분극 시험을 실시하였다. 희생양극 소모율에 대한 전착물의 영향을 확인하기 위해 외부전원을 인가하여 전착 피막을 형성시킨 강 기판에 희생양극을 연결하여 희생양극 소모효율 측정 시험을 진행하였다. 전착물의 석출량은 시간 및 전류밀도의 증가에 따라 비례하여 증가하였으며, 음극전류 인가 시 금속과 용액 계면 사이의 확산층에서 발생한 $OH^-$ 이온으로 인해 금속과 용액 계면 사이 pH가 부분적으로 증가하여 $Mg(OH)_2$ 화합물이 많이 생성되는 것으로 확인되었다. 또한 Mesh의 부착으로 평활하지 않게 형성된 미세한 굴곡구조 및 표면적 증가로 인하여 단계적으로 피복되는데 필요한 시간이 지연되면서 $CaCO_3$에 비해 $Mg(OH)_2$ 화합물이 상대적으로 증가한 것으로 사료된다. $CaCO_3$(Aragonite) 구조는 견고한 피막으로 치밀하고 화학적 친화력이 높아 우수한 밀착성을 보였으며 전착물의 영향으로 양극 전류가 감소하였고, 이로인해 방식전류 절감효과를 얻을 수 있을 것으로 기대된다.

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.2 no.1
• /
• pp.1-9
• /
• 2014

In this paper, $CO_2$ amount is evaluated considering repairing timing and unit $CO_2$ amount per repair method including various stage of material manufacturing, moving, and construction. Four mix proportions with mineral admixture are considered and repairing timing/numbers are simulated based on the results from Life 365 which can handle chloride penetration. Furthermore two repair methods (simple cover concrete replacement and replacement with electro-chemical method for removing chloride content) are considered and the related $CO_2$ emissions are evaluated. From the study, the case with high W/B (water to binder ratio) ratio shows smaller $CO_2$ emission in construction stage but it increases more rapidly with increasing number of repair. $CO_2$ emission considering electro-chemical method greatly increases with the increasing unit $CO_2$ for the repairing method. The numbers of jumping step (repairing number) are evaluated to be 9 for WB37-OPC, 18 for WB50-OPC, 4 for WB40-SG, and 7 for WB47-SG respectively. RC structures with the longer maintenance free period are evaluated to be advantageous for saving $CO_2$ emission.

• Journal of the Mineralogical Society of Korea
• /
• v.19 no.3 s.49
• /
• pp.129-138
• /
• 2006

In this study, we identified the secondary precipitates from Samsan-jeil and Sambong mine, Goseong, Gyeongnam by means of scanning electron microscopy, electron probe microanalysis and X-ray powder diffraction analysis. Copper sulfide minerals had been produced from the mines during last few decades, however they are not worked. White and blue precipitates were found at the downstream of mine rock dump at Sambong mine and green one was at Samsan-jeil mine. The white precipitate covered the host rock surface with thickness of $30{\mu}m$, and is a kind of diatom with $10{\mu}m$ in length and $3{\mu}m$ in width. It is a species Fragilaria constuens, which is contained a order Pennales(pennate diatom) and lives in fresh water. The blue precipitate is the alteration product of chalcopyrite. It resultes in the increase in the ratio Cu:Fe from 5 to 13. The green precipitate has worm-like morphology with $10{\sim}20nm$ in diameter and $200{\sim}300nm$ in length. It is mainly composed of secondary copper sulfate such as woodwardite. However, it could be formed by the activity of microorganism, because the copper content is more than any secondary copper sulfate reported in copper sulfide mine. In order to identity the green precipitate exactly, the further research is needed.

• Journal of the Korean association of regional geographers
• /
• v.2 no.1
• /
• pp.39-49
• /
• 1996

There is a limestone basin surrounded by the mountains consisted of Paleozoic sedimentary and metamorphic rocks in the Masung, Munkyung city, Kyungsangpook do. The purpose of this paper is to elucidate the geomorphic processes of the gentle hillslopes in the marginal piedmont of Masung basin. To do so, I analyzed deposits over hillslopes and the relation ship between the distance from the divide and the height(above sea level) at the longitudinal profile of the hillslope, and considered interrelation between the distributions of the gentle hillslopes(less than 230m) and lithology. Geomorphic processes of Masung basin are as follow: (1) The depth of deposits over hillslope increases toward downstream of the hillslope. Most gravels within deposits, whose lithology is limestone, are those eroded at the boundary(overthrust fault zone) between the back-mountain and the hillslope. Deposits at the outward margin of hillslope is well sorted. and moderately imbricated. (2) Hillslope at the margin of the basin(160-230m asl) is formed by the action of 'the flow with channel'. At the boundary between the soft rock(limestone; basin floor) and hard rock(sedimentary and metamorphic rock; back-mountain), the relatively weak limestone is eroded to fresh bedrock by the subsequent action of the overland flow, and therefore discontinuity in slope appeared. (3) After hills lopes were formed, sediments(boulders and fine material) produced during dissection in back-mountain buried deposits over hillslope. In conclusion, geomorphic processes of Masung basin is 'differential erosion due to differentiation of lithological hardness' having suggested as geomorphic processes of granitic basin. However it is not 'removal of weathering material due to sheetflow' but 'erosion due to the overland flow with channel'.

• Journal of the Korea Concrete Institute
• /
• v.22 no.2
• /
• pp.199-208
• /
• 2010

In order to substitute FRP bar for steel bar in new structures, it is necessary to establish a reliable design code. But relatively little research has been conducted on the material in Korea. So, a total of 22 beam specimens (18 GFRP reinforced concrete and 4 conventional steel reinforced concrete) were constructed and tested. In the first phase of the experiment, it was carried out to observe flexural behavior, and collect deflection and crack data. In order to eliminate of the uncertainty by the shear reinforcements and induce flexural failure mode, any stirrup were not used and only shear span-depth ratio were adjusted. However, almost beams were broken by shear and the ACI 440.1R, CSA S806, which were used to design test beams, showed considerable deviation between prediction and test results of shear strengths. Therefore in the second phase of the study, shear failure modes and behavior were observed. A standard specimen had dimensions of 3,300 mm long ${\times}$ 800 mm wide ${\times}$ 200 mm effective depth. Clear span and shear span were 2,800 mm, 1,200 mm respectively. Control shear span-depth ratio was 6.0. Four-point bending test over simple support was conducted. Variables of the specimens were concrete compressive strength, type and elastic modulus of reinforcement, shear span-depth ratio, effective reinforcement ratio, the effect of bundle placing method and cover thickness.

• 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.

• Journal of the Korea Concrete Institute
• /
• v.29 no.1
• /
• pp.109-116
• /
• 2017

The present study concerns quantitative assessment of chloride extraction, repassivation and structural behavior of concrete. Concrete specimen ($160{\times}160{\times}1000mm$) was fabricated with 3 steel bar located in the middle with 20 mm of the cover depth, containing 5.0% of chloride to accelerate corrosion process, then to be subjected to electrochemical treatment. The current density accounted for $750mA/m^2$ at 2, 4 and 8 weeks. As a result, it was found that an increase in the duration of the treatment resulted in an increase in the chloride extraction, accounting for 64.7-83.7% for the specimen at 8 weeks treatment. It implies that a portion of bound chlorides would turn free to be removed, considering the binding capacity of cement about 50-60% to total ones. Even after the treatment, the corrosion was still active; the corrosion rate was $6.5mA/m^2$ and 330 mV vs. SCE in the potential. For structural behavior, the maximum load was increased by corrosion on the steel bars, which was subsequently lowered by the treatment, but still higher than for control.

• Journal of Ocean Engineering and Technology
• /
• v.30 no.4
• /
• pp.327-333
• /
• 2016

Reinforced concrete structures have found wide usage in land and maritime applications. However, the corrosion of reinforced concrete has been recognized as a serious problem from economic and safety standpoints. In previous studies, the corrosion behavior of the inner steel bar embedded in mortar (W/C: 0.4, 0.5) was investigated using electrochemical methods. In this study, multiple mortar test specimens (W/C: 0.6) with six different cover thicknesses were prepared and immersed in flowing seawater for five years. Subsequently, equations related to the cover thickness, period of immersion, and corrosion characteristics of the embedded steel bar were evaluated using electrochemical methods. Prior to immersion, the corrosion potentials indicated an increase with increasing cover thickness, and after five years, all corrosion potentials demonstrated a trend in the positive direction irrespective of the cover thickness. However, the relationships between the corrosion potential and cover thickness were not in complete agreement. Furthermore, after five years, all of the corrosion potentials indicated values that were nobler compared to those obtained prior to immersion, and their corrosion current densities also decreased compared to their values obtained prior to immersion. It was considered that the embedded steel bar was easily corroded because of the aggression of water, dissolved oxygen, and chloride ions; a higher W/C ratio also assisted the corrosion process. The corrosive products deposited on the surface of the steel bar for five years cast a resistance polarizing effect shifting the corrosion potential in the nobler direction. Consequently, it was considered that the W/C ratio of 0.6 showed nearly same results as those of W/C of 0.4 and 0.5. Therefore, the corrosion potential as well as various parameters such as the cover thickness, period of immersion, and W/C ratio must be considered at once for a more accurate evaluation of the corrosion property of reinforced steel exposed to marine environment for a long period.

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.9 no.3
• /
• pp.236-245
• /
• 2021

It is very important for structure designer to understand the service life variation since a wide range of service life is evaluated with changing exposure conditions and design parameters. Recently, for zero-carbon, waste plastic has been used for fuel for clinker production and this yields increase in chloride content in cement. This study is for evaluation of changing service life in the concrete with increasing initial chloride content due to usage of plastic-SRF(Solid Refuse Fuel) considering various exposure conditions and design parameters. For this, 4 levels of initial chloride content were assumed, and the service life was assessed using LIFE 365 program considering various environmental conditions including 3 levels of surface chloride content. As for analysis parameters, critical/initial chloride content, blast furnace slag powder replacement ratio, W/B(Water to Binder) ratio, cover depth, and unit mass for binder are adopted. Service life decreases with increasing initial chloride content and a significant reduction of service life is not evaluated permitting up to 1,000ppm of initial chloride content. With increasing slag replacement ratio, a longer service life can be secured since blast furnace slag powder has the effect of reducing the diffusion of external chloride ions and fixing the free chloride. It is thought that increasing initial chloride content up to European standard is helpful for enhancing sustainability and reducing carbon emission. Though the reduction in service life due to an increase in the initial chloride content is not significant in slag-concrete with low surface chloride content, careful consideration for mixing design should be paid for the exposure environment with high surface chloride content.