• International Journal of Concrete Structures and Materials
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• v.11 no.2
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• pp.199-213
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• 2017

Chloride penetration is among the main causes of corrosion initiation in reinforced concrete (RC) structures producing premature degradations. Weather and exposure conditions directly affect chloride ingress mechanisms and therefore the operational service life and safety of RC structures. Consequently, comprehensive chloride ingress models are useful tools to estimate corrosion initiation risks and minimize maintenance costs for RC structures placed under chloride-contaminated environments. This paper first presents a coupled thermo-hydro-chemical model for predicting chloride penetration into concrete that accounts for realistic weather conditions. This complete numerical model takes into account multiple factors affecting chloride ingress such as diffusion, convection, chloride binding, ionic interaction, and concrete aging. Since the complete model could be computationally expensive for long-term assessment, this study also proposes model simplifications in order to reduce the computational cost. Long-term chloride assessments of complete and reduced models are compared for three locations in France (Brest, Strasbourg and Nice) characterized by different weather and exposure conditions (tidal zone, de-icing salts and salt spray). The comparative study indicates that the reduced model is computationally efficient and accurate for long-term chloride ingress modeling in comparison to the complete one. Given that long-term assessment requires larger climate databases, this research also studies how climate models may affect chloride ingress assessment. The results indicate that the selection of climate models as well as the considered training periods introduce significant errors for mid- and long- term chloride ingress assessment.

• Journal of the Korea institute for structural maintenance and inspection
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• v.14 no.2
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• pp.171-175
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• 2010

This paper presents the experimental results of frost durability characteristics including freezing-thawing and de-icing salt scaling of the concrete for gutter of the road and marine structure. Mixtures were proportioned with the three level of water-binder ratio(W/B) and three binder compositions corresponding to Type I cement with 0%, 30% and 50% GGBS(Ground granulated blast furnace slag) replacement. Also, two different solutions of calcium chloride were used to evaluate their effect on the frost durability resistance. Specially, in case of complex of freezing and thawing with salt and carbonation, the deterioration of concrete surface is evaluated. Test results showed that the BFS30 and BFS50 mixture exhibited higher durability and lower mass loss values than those made with OPC mix and the use of GGBS can be used effectively in terms of economy and frost durability of the concrete to be in complex deterioration. Therefore, the resistance to complex deterioration with freezing-thawing was strongly influenced by the strength and the type of cement.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.41 no.4
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• pp.417-428
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• 2021

Since future maintenance cost estimation of infrastructure involves uncertainty, it is important to make use of a failure prediction model. However, it is difficult for local governments to develop accurate failure prediction models applicable to infrastructure due to a lack of budget and expertise. Therefore, this study estimated the life expectancy of asphalt road pavement of national highways using the Bayesian Markov Mixture Hazard model. In addition, in order to accurately estimate life expectancy, environmental variables such as traffic volume, ESAL (Equivalent Single Axle Loads), SNP (Structural Number of Pavement), meteorological conditions, and de-icing material usage were applied to retain reliability of the estimation results. As a result, life expectancy was estimated from at least 13.09 to 19.61 years by region. By using this approach, it is expected that it will be possible to estimate future maintenance cost considering local failure characteristics.

• Structural Engineering and Mechanics
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• v.84 no.3
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• pp.393-411
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• 2022

A high-performance reactive powder concrete (RPC) has been readied alongside river sand, with 1.25 mm particle size when under the condition of 80C steam curing. As a heat and sound insulation, expanded perlite aggregate (EPA) provides economic advantages in building. Concrete containing EPA is examined in terms of cement types (CEM II 32.5R and CEM I 42.5R), doses (0, 2%, 4% and 6%) as well as replacement rates in this research study. The compressive and density of concrete were used in the testing. At the end of the 28-day period, destructive and nondestructive tests were performed on cube specimens of 150 mm150 mm150 mm. The concrete density is not decreased with the addition of more perlite (from 45 to 60 percent), since the enlarged perlite has a very low barrier to crushing. To get a homogenous and fluid concrete mix, longer mixing times for all the mix components are necessary due to the higher amount of perlite. As a result, it is not suggested to use greater volumes of this aggregate in RPC. In the presence of de-icing salt, the lightweight RPC exhibits excellent freeze-thaw resistance (mass is less than 0.2 kg/m²). The addition of perlite strengthens the aggregate-matrix contact, but there is no apparent ITZ. An increased compressive strength was seen in concretes containing expanded perlite powder and steel fibers with good performance.

• Journal of Energy Engineering
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• v.11 no.1
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• pp.1-9
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• 2002

The purpose of this study is to maintain high efficiency and reasonable use of cool thermal storage systems operated in the domestic building sector. As the result of efficiency test from the five types of operated cool storage systems on the condition that COP ranges are 2.6 to 3.4 during the day time and 2.1 to 3.0 during the night time and it decreased by more than 30% of rated COP given 3.8 to 3.0. The Analysis of cool storage rate shows that only 3 (21.4%) systems out of 15 buildings hold to over 40% capacity for its total capacity. To prevent the decrease in operating efficiency, it should correct the malfunction of 3-way valve and expansion valve and the mistake of control values for schedule program and increase cooling tower capacity. In order to improve piping line, it needs bypass brine line off refrigerator, separation of chilled water line with Ice Slurry system at day and night time and speed control of chilled and warm water pumps. This study does require the more studies on improving difficulty of increasing cooling load with Ice on Coil system, waterproofing with Ice Ball system, COP drop during the night time with Ice Lens, low operating temperature during the day time with Ice Slurry and increasing of Power loss due to hot gas de-icing with Ice Harvest in the future.

• Ecology and Resilient Infrastructure
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• v.3 no.4
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• pp.272-278
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• 2016

Porous pavements are recommended as a Low-Impact Development (LID) method which is a strategy to develop a water cycle as close to a natural state as possible, and to solve the urban impervious surface problems. Porous pavements can yield a solution if it provides a more permeable surface with extra space to contain extra water from building roofs. But there are few applications in Korea because of a lack of recognition and experience. Highway engineers are mainly concerned about the infiltration of water into pavement structures. They worry about the weakening of the asphalt mixture and subgrade, and freezing during the winter season due to the infiltration of water. Meanwhile, hydrological experts doubt the effects of the amount of water to control during the flooding season, and environmental experts prefer a non-point pollution treatment system established beside highway. In this study, from reviewing the history and the body of literature about porous pavements, conclusions regarding the most advanced technologies were made. First, traditional thickness designs can be used for porous pavement, no extra distresses was found by weakening and freezing during the winter season. Second, hydrological design can be made by controlling the thickness of the pavement and the outlet of water. Third, the treatment efficiency of non-point pollution of porous pavements is not worse than any other method. Importantly, it's a more eco-friendly solution because of its lower requirement for de-icing agents.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.4
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• pp.2391-2400
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• 2015

Weather proof steels are used for steel bridges due to its high corrosion resistance under atmospheric conditions. However, instead of forming stabilized rust layers, general rust occurs on weather proof steels under high humidity condition close to seawater or shady places. In Japan, therefore, they perform rust stabilization treatment instead of unpainted treatment due to severe atmospheric conditions. However, most of domestic weather proof steels were constructed unpainted in the form of closed box-girder, which makes the periodical repetition of dry and wet hard to occur. For the steel bridges constructed on the Han river, the evaporation of water, dew condensation due to temperature change, and stagnant water due to rain affect harmfully on the formation of passive film on weather proof steels. Thus, in this research, in order to analyze corrosion properties inside the closed box-girder for the unpainted weather proof steel bridge in the waterworks safety zone, multiple ways of analysis such as observation with eyes, cellophane-tape test, steel thickness measurement, surface corrosion potential measurement, electron microscope analysis, and X-ray diffraction analysis of the rust were performed. As a result, unstable rust layer was observed inside the closed box-girder, and severe corrosion was observed on the top and bottom of the flanges due to the effects of stagnant water caused by rain, dew condensation, and de-icing materials.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.25 no.5
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• pp.205-211
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• 2015

Most of the sulfur is obtained from desulfurization of natural gas and crude oil. In Korea, more than 120 tons of sulfur are produced by refinery, and about 50 % of the produced sulfur is used as a raw material for the production of fertilizer and sulfuric acid. Modified sulfur is manufactured from excessive sulfur that could be used to improve concrete properties, and this study evaluated concrete strength and durability that contains modified sulfur. Flexural and compressive strengths of concrete with sulfur modified polymer were comparable to those of OPC concrete with mixing water at similar temperatures, while the strengths increased a little as mixing water temperature increased. It was also confirmed that the resistance to freeze-thaw damage was more dependent on entrained air characteristics obtained by a proper use of air entraining agent than on the use of sulfur modified polymer. When concrete was immersed in 5 % sulfuric acid, the rate of reduction in compressive strength of OPC concrete was less than 1/4 of the strength reduction of concrete with sulfur modified polymer. Also, the resistance of concrete with sulfur modified polymer to scaling due to the use of de-icing salt was evaluated as Class 1, while that of OPC concrete was evaluated as Class 4, as aggregates were exposed. Accordingly, it is believed that sulfur modified polymer could be effectively used for bridge deck concrete since sulfur modified polymer improves the durability of concrete.

• Journal of the Korean Institute of Landscape Architecture
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• v.41 no.4
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• pp.17-23
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• 2013

The purpose of this study was to provide information on management and apply it to a roadside ground cover plant understanding the capacity of calcium chloride in the plant. The experimental group was composed of the ratio control group of calcium chloride, 0.5%, 1.0%, and 3.0% in 500g of soil. Plant materials were selected and measured according to their ecological characteristics such as ground cover plant, Pachysandra terminalis, Hosta plantaginea, Trachelospermum asiaticum, Vitex rotundifolia, Euonymus japonica and Callicarpa japonica. The acidity of the amended soil was increased gradually depending on the treatment and conductivity was continually decreased. The EX-Ca increased after the treatment, but decreased in the middle of the experiment. Pachysandra terminalis, Trachelospermum asiaticum and Euonymus japonica were able to grow and survive at the ratio of 0.5%. Hosta plantaginea and Vitex rotundifolia were able to survive at the ratio of 1.0%. Hosta plantaginea, the possible state can absorb salts due to moisture and, can be applied to ground cover plants in the roadside. The growth and development of Callicarpa japonica was poor and the leaves were open to grow for calcium chloride treatment except the control group. It was concluded that Callicarpa japonica was very sensitive to calcium chloride.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1999.04a
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• pp.22-22
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• 1999

교란에 대한 고체 추진제의 연소율의 반등에 대한 이해는 고성능 추진제를 설계하는데 매우 중요한 요소이다. 그 동안의 연구는 고체 추진제의 표면에서 발생하는 교란이 매우 작은 크기로 발생한다는 선형적인 가정을 사용하여 이론적인 응답 함수를 구하였다. 특히 실험실에서 행해지는 교란에 대한 추진제의 응답 함수를 구하기 위하여 이용한 비집촉식 교란 방법을 사용하였다. 이 경우 추진제 표면으로 전달되는 복사열 전달의 크기는 레이저에 의한 복사 일전달과 기체 영의 화염에 의한 열전달을 동시에 고려하여야 한다. 그러나 언급하였던 것처럼 대부분의 이론적 연구는 추진제 표면의 온도 구매가 단열인 것으로 가정하여 진행하였다. 이러한 가정을 기체 영역으로부터 추진제로 전달되는 열전달 량이 작은 점소화초기 등에서 타당한 가정이나, 기체 영역에서 연소가 활발하게 진행되는 경우에는 비합리적인 가정이다. 본 연구에서는. 추진제의 응축 영역에서 분포 화학 반응이 발생하여, 기체 영역에서 화학반응에 의한 연소가 진행되는 경우, 복사 열전달의 교란에 대한 추진제의 응답함수를 수치적으로 계산하였다. 이때 기체 영역에서 발생하는 연소 반응은 De Luca 등에 의하여 제안된 실험적 모델인 $\alpha$ $\beta$ ${\gamma}$ 화염 모델을 사용하였으며, 추진제 표면에서의 열전달 균형에 의한 경계 조건을 사용하였다. 그러나 외부로부터 입사되는 복사광 레이저와 기체 영역의 상호 간섭은 고려하지 않았다. 수치 계산에 의한 응답 함수의 특징은 단열 조건이 사용된 이론적 응답 함수에 비하여 낮은 값을 나타내었으며, 최대치를 보이는 주파수 영역도 이론 함수에 비하여 다른 값을 보여주고 있다.연구 분석 결과 기술적 문제점으로는 배기 가스온도가 낮은데 따른 출구 부분의 Bearing, Sealing이 문제가 될 수 있다고 판단되며 배기 가스 자체에 대기 공기중에 함유되어 있던 습기가 얼어붙는(Icing화) 문제가 발생하기 때문에 배기가스의 Icing을 방지하기 위하여 압축기 끝단에서 공기를 추출하여 배기부분에 송출할 필요성이 있는 것으로 판단되었다. 출구가스의 기체 유동속도가 매우 빠르므로 (100-l10m.sec) 이를 완화하기 위한 디퓨저의 설계가 요구된다고 판단된다. 또 연소기 후방에 물을 주입하는 경우 열교환기 및 기타 부분품에 발생할 수 있는 부식 및 열교환 효율 저하도 간과할 수 없는 문제로 파악되었다. 이러한 기술적 문제가 적절히 해결되는 경우 비활성 가스 제너레이터는 민수용으로는 대형 빌딩, 산림, 유조선 등의 화재에 매우 적절히 사용되어 질 수 있을 뿐 아니라 군사적으로도 군사작전 중 및 공군 기지의 화재 그리고 지하벙커에 설치되어 있는 고급 첨단 군사 장비 등의 화재 뿐 아니라 대간첩작전 등에 효과적으로 활용될 수 있을 것으로 판단된다.가 작으며, 본 연소관에 충전된 RDX/AP계 추진제의 경우 추진제의 습기투과에 의한 추진제 물성 변화는 미미한 것으로 나타났다.의 향상으로, 음성개선에 효과적이라고 사료되었으며, 이 방법이 편측 성대마비 환자의 효과적인 음성개선의 치료방법의 하나로 응용될 수 있으리라 생각된다..7%), 혈액투석, 식도부분절제술 및 위루술·위회장문합술을 시행한 경우가 각 1례(2.9%)씩이었다. 13) 심각한 합병증은 9례(26.5%)에서 보였는데 그중 식도협착증이 6례(17.6%), 급성신부전증 1례(2.9%), 종격동기흉과 폐염이 병발한 경우와 폐염이 각 1례(2.9%)였다. 14