• Journal of the Korea Concrete Institute
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• v.22 no.5
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• pp.641-650
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• 2010

The concrete cracking from the restrained stress caused by the shrinkage may play significant cause of deterioration of concrete structures by allowing the permeation of sulphate and chloride ions which in turn triggers corrosion of steel reinforcement. In particular, the cracking becomes more critical as water binder ratio (W/B) is reduced and concrete strength increases. Therefore, it needs to evaluate correctly the comprehensive shrinkage behavior of concrete with high strength: high-strength concrete (HSC), ultra-highstrength concrete (UHSC). The unrestrained shrinkage tests, however, cannot estimate the net shrinkage effectively which affects cracking after full development of strength and stiffness because it does not consider the degree of restraint, strength development, stress relaxation, and so on. Therefore, in this study, both free and restrained shrinkage tests with variables of W/B (W/B of 30, 25 and 16%) and admixtures (fly ash (FA) and granulated blast-furnace slag (BFS)) for HSC, very-high-strength concrete (VHSC) and UHSC were performed. The test results indicated that the autogenous shrinkage and total shrinkage at drying condition were reduced as W/B increased and FA, BFS were added, and the cracking behavior was suppressed as W/B increased and FA was added.

• Journal of Conservation Science
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• v.26 no.2
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• pp.149-156
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• 2010

One of resins, V-Flon is useful as a coating material because YK-D80, which is a solvent for V-Flon, is not highly volatile. However, it can not completely harden and can flow out when metal artifacts are joined and restored in the process of the treatment. Therefore, after the impregnation process in order to accelerate the hardening speed of a coating material, usually a dry oven was adopted. This study focused on finding the problems on the dry oven which is employed to increase the speed and investigating the most effective solvent and its composition by checking any change occurred depending on the concentration of solvents. Six different types of solvents were selected and samples were prepared in a manner that they were impregnated with solvents in three concentrations respectively (10%, 20%, 30%). To determine the condition of the samples, the stability evaluation was performed by measuring the change of color and the gloss, the thickness of coated layers, the corrosion after coating, the water resistance by contact angles. Through the comparative experiments between the natural drying and the artificial drying using a dry oven, it was found that when the dry oven is used, some problems are identified on the point of forming a uniform and stable layer because of the unstable data collected from the forced artificial dry. The experiments performed using 3 different concentration rates (10%, 20%, 30%) presented that in the case of 10% V-Flon in Xylene (using as a solvent), its layer was thin as well as it showed the high water-barrier property, which allows it to form the stably coated layer with the lower gloss and color change.

• Journal of the Society of Disaster Information
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• v.8 no.3
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• pp.223-233
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• 2012

Steel fiber is high stiffness and large weight. So, Pumping hose to rupture of the safety management is difficult. Steel fiber caused by corrosion of the deterioration of durability and high-rebound losses are needed for the improvements. Thus, the revised regulations in 2009 by a steel fiber to reinforce other materials is possible. Variety of fiber reinforcement material for concrete review of applicability is needed. Steel fiber strength than the other fibers is large and by the geometry of the fibers are attached to improve performance. However, compared to steel fiber organic fibers and low modulus of elasticity and tensile strength of fiber and agglomeration occurs in the concrete to be used as reinforcement material is difficult. In this regard, the present study as a single object in the micro-fiber bouquet sharp entanglement through make muck attach surface area, distributed fibers from surfactant of the surface enhanced polyamide fibers, steel fiber and PP fiber reinforced concrete by comparing the scene to provide a basis for the use.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.6
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• pp.132-139
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• 2017

A huge amount of de-icing agent is sprayed during winter to promote traffic safety in cold regions, and the quantity of de-icing agent sprayed has increased each year. The main ingredients in commonly used de-icing agents are chlorides, such as calcium chloride($CaCl_2$) and sodium chloride(NaCl). While calcium chloride is mostly used in Korea and sodium chloride is usually used in the U.S. and Japan, all de-icing agents include chloride ions. The chlorides included in sprayed calcium chloride-based de-icing agents have severe adverse effects, including the corrosion of reinforcing steels through salt damage by infiltrating into road structures, reduced structural performance of pavement or damage to bridge structures, and surface scaling, in combination with freezing damage in winter, as well as water pollution. In addition, the deterioration of paved concrete road surface that occurs after the use of calcium chloride-based de-icing agent accelerates the development of visual problems with traffic structures. Therefore, the present study was performed to prepare an environment-friendly liquid de-icing agent through a reaction between waste organic acids and calcium-based by-products, which are industrial by-products, and to analyze the properties of the de-icing agent in order to evaluate its applicability to road facilities.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.4
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• pp.52-59
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• 2018

To control chloride attacks which is a representative deterioration in RC(Reinforced Concrete) structures, many studies have been conducted. Above all, a method using mineral admixture was known to be effective for corrosion protection. In this study, durability test about chloride attacks was carried out for concrete specimens containing FA(Fly Ash)-representative concrete mineral admixture and OPC concrete specimens considering 3 different levels of W/B(Water to Binder). Accelerated chloride diffusion coefficient tests referred to Tang's method, total passed charge tests referred to ASTM C 1202, and compressive strength tests based on KS F 2405 were performed at each target age day. Also, based on previous studies of 28 days, time-parameter which is a key parameter for diffusion behavior is evaluated and its relations with compressive strength at the age of 365 days is evaluated. After the age of 49 days, chloride resistance of FA concrete is much improved than that of OPC concrete, which arose out of stable hydrates due to pozzolan reaction of fly ash. Time-parameter of FA concrete is evaluated to be about 1.5 times larger than that of OPC concrete. Also, time-parameter of FA concrete has a linearly decreasing relation while that of OPC concrete has a linearly increasing relation with compressive strength development.

• Journal of Periodontal and Implant Science
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• v.31 no.4
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• pp.749-763
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• 2001

Osseointegrated titanium implants have become an integral therapy for the replacement of teeth lost. For dental implant materials, titanium, hydroxyapatite and alumina oxide have been used, which of them, titanium implants are in wide use today. Titanium is known for its high corrosion resistance and biocompatability, because of the high stability of oxide layer mainly consists of $TiO_2$. With the development of peri-implantitis, the implant surface is changed in surface topography and element composition. None of the treatments for cleaning and detoxification of implant surface is efficient to remove surface contamination from contaminated titanium implants to such extent that the original surface elemental composition. In this sights, the purpose of this study was to evaluate rough surface titanium implants by means of scanning electron microscopy(SEM) and X-ray photoelectron spectroscopy(XPS) with respect to surface appearance and surface elemental composition. Moreover, it was also the aim to get the base for treatments of peri-implantitis. For the SEM and XPS study, rough surface titanium models were fabricated for control group. Six experimental groups were evaluated: 1) long-time room exposure, 2 ) air-powder abrasive cleaning for 1min, 3) burnishing in citric acid(pH1) for 1min, 4) burnishing in citric acid for 3min, 5) burnishing in tetracycline for 1min, 6) burnishing in tetracycline for 3min. All experimental treatments were followed by 1min of rinsing with distilled water. The results were as follows: 1. SEM observations of all experimental groups showed that any changes in surface topography were not detected when compared with control group. (750 X magnification) 2. XPS analysis showed that in all experimental groups, titanium and oxygen were increased and carbon was decreased, when compared with control group. 3. XPS analysis showed that the level of titanium, oxygen and carbon in the experimental group 3(citric acid treatment for 1min, followed by 1min of distilled water irrigation) reached to the level of control group. 4. XPS analysis showed that significant differences were not detected between the experimental group 1 and the other experimental groups except of experimental group 3. The Ti. level of experimental group 2, airpowder abrasive treatment for lmin followed by 1min of saline irrigation, was lower than the Ti. level of tetracycline treated groups, experimental group 5 and 6. From the result of this study, it may be concluded that the 1min of citric acid treatment followed by same time of rinsing with distilled water gave the best results from elemental points of view, and can be used safely to treat peri-implantitis.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2016.11a
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• pp.163-163
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• 2016

아연계 도금 강판은 우수한 내식성을 가지며 특히 아연의 희생방식기구에 의해 철의 부식을 억제하므로 선박, 건축자재, 전자기기 및 자동차 등 다양한 분야에서 그 수요와 사용범위가 증가하고 있다. 또한 도금 조성비 변화 및 다양한 표면처리 방법을 통해 가혹한 환경에서의 우수한 내식성에 대한 연구가 활발히 진행되고 있다. 그 중 갈바륨(Galvalume)은 55%의 알루미늄(Al)과 45%의 아연(Zn)으로 되어 있으며, 아연의 장점인 희생방식성과 내알카리성, 알루미늄의 장점인 내구성과 내열성, 내산성을 이상적으로 결합시킨 알루미늄(Al)-아연(Zn) 고내식 합금용융도금강판이다. 본 연구에서는 갈바륨 소재를 여러 산업현장에서 강관 형태로 사용할 경우의 내식성을 파악하기 위해 갈바륨 강관과 기존에 사용되고 있는 용융도금재인 용융아연도금 강관을 비교하며 실험을 진행하였다. 냉간압연강관에 용융아연도금 약 $25{\mu}m$, 갈바륨 약 $20{\mu}m$ 두께로 제작된 강관을 사용하였으며 제작된 도금층 표면 모폴로지는 SEM을 통해 관찰하였고, XRD 분석을 통해 결정 구조를 확인하였다. 또한 5% 염수분무 환경 중 노출시험(Salt spray test), 3% NaCl 용액에서의 자연침지 시험 및 3% NaCl 용액 중 전기화학적 양극분극 시험을 진행하여 평가하였다. 5% NaCl 환경에서의 염수분무 시험 결과 용융아연도금의 경우 단면에서는 90시간, 표면에서는 260시간 경과 후 적청이 발생하였다. 반면, 갈바륨의 경우에는 단면에서 210시간 경과 후에 적청이 발생하였고, 표면의 경우에는 900시간 이상에서도 적청이 발생하지 않았다. 이 결과를 통해 용융아연도금에 비해 갈바륨 도금의 내식성이 단면에서는 3배, 표면에서는 4~5배 이상 향상된 것으로 확인되었다. 또한 3% NaCl 용액 중 자연침지 시험 결과 용융아연도금 강관 표면은 24시간 경과 후 열화부를 중심으로 흑변하는 것을 확인할 수 있었으나 갈바륨의 경우에는 900시간 이상 실험이 진행되는 동안 No Scribe 및 Scribe 시편 모두 외관상 변화가 거의 없었다. 단면의 경우, 용융아연도금 시편은 900시간 이상 실험이 진행되는 동안 외관상 변화가 없었으며, 갈바륨 시편의 경우 300시간 경과 하면서 흰색의 아연 부식생성물이 나타났으나 900시간 이후로도 적청은 발생하지 않았다. 자연전위 측정결과 용융아연도금 및 갈바륨 시편 모두 유사한 전위거동을 나타냈지만 단면의 경우 갈바륨 시편이 용융아연도금에 비해 안정적인 거동을 보였다. 3% NaCl 용액 중 전기화학적 양극 분극 시험 결과 용융아연도금이 갈바륨에 비해 귀한 방향의 부식 전위 값을 나타냈으며, 부식 전류밀도도 용융아연도금이 갈바륨에 비해 더 높은 값을 나타내는 것을 확인할 수 있었다. 이상의 염수분무시험, 자연침지시험 및 전기화학적 양극분극시험을 통해 종합적으로 분석-고찰하여 보면, 그 부식이 진행되는 과정은 융융아연도금과 달리 갈바륨 도금의 경우가 다단계적인 부식 과정을 거치면서 우수한 내식 특성을 나타낸다는 것을 알 수 있었다. 즉, 갈바륨 도금은 그 도금 막에 분포된 합금상 원소 성분들이 상호 갈바닉(Galvanic) 작용하며 형성된 부식생성물이 수평적으로 자체 차단(Barrier) 역할을 하는 과정과 부분적 부식-회복 과정을 거치면서 다단계적으로 부식속도를 감소시키게 된다는 것을 확인 할 수 있었다.

• Journal of the Korean Institute of Gas
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• v.18 no.4
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• pp.76-85
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• 2014

To establish the necessary safety technology in high-pressure toxic gas facilities, especially for the corrosion, which is the main causes of toxic gas accident, this study adopts and investigates the API-581 procedures developed by the American Petroleum Institute (API). And the applicability of the 8-step analytical procedures of consequence analysis in API-581 is discussed, and a method for consequence analysis in high-pressure toxic gas facilities is suggested. Based on the discussion and results, the analytical procedure is simplified as the 6 steps in total for the effective application to high-pressure toxic gas facilities: Step 1 (determination of representative material), Step 5 (determination of release type), Step 6 (determination of phase of fluid), and Step 8 (estimation of damage range) are not applied: Step 3 (estimation of total amount of release) is applied only for the inventory group concept; Step 4 (estimation of release rate) only for the gas release rate; and all of Step 2 (selection of release hole size) and Step 7 (evaluation of post-release response) are applied. In the proposed method, the generally applicable method of CCPS is adopted as alternative method for Steps 5 and 8.

• Journal of the Korea Institute of Building Construction
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• v.16 no.2
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• pp.107-115
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• 2016

In this study, the bond strength of metal spraying system by surface treatment of concrete (waterproof/corrosion method) in water treatment facilities was evaluated. The results showed that the system with Sa-P-R-(S) (sanding-perviousness surface hardener-surface roughness agent-metal spraying-sealing) led to the desirable performance. The bond strength, the coefficient of water permeability and air permeability were 3.7MPa, $0.68{\ast}10^{-8}cm/sec$, and $0.45{\ast}10^{-16}m^2$, respectively. In scanning electron microscope analysis, the microstructure of specimen coated with perviousness surface hardener was much denser than that without it. Therefore, the specimen coated with sanding-perviousness surface hardener-surface roughness agent-metal spraying-sealing had the best bond performance and was the most suitable system to concrete surface in water treatment facilities.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.5
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• pp.83-91
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• 2015

With varying conditions of concrete surface, induced chloride contents are changed and this is a key parameter for steel corrosion and service life in RC (Reinforced Concrete) structures. Many surface enhancement techniques using impregnation have been developed, however the evaluation techniques for chloride behavior through doubly layered media and time-dependent diffusion are rarely proposed. This paper presents an analysis technique considering double-layer concrete and time-dependent diffusion behavior, and the results are compared with those from the previous test results through reverse analysis. The chloride profiles from the surface-impregnated concrete exposed to atmospheric, tidal, submerged zone for 2 years are adopted. Furthermore surface chloride contents and diffusion coefficients are obtained, and are compared with those from Life365. Through consideration of time effect, the relative error decreases from 0.28 to 0.20 in atmospheric, 0.29 to 0.11 in tidal, and 0.54 to 0.40 in submerged zone, respectively, which shows more reasonable results. Utilizing the diffusion coefficients from Life365, relative errors increases and it needs deeper penetration depth (e) and lower diffusion coefficient ratio ($D_1/D_2$) due to higher diffusion coefficient.