• 한국건설순환자원학회논문집
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• 제5권1호
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• pp.1-7
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• 2017

초기재령에서의 콘크리트 거동은 시간의 증가에 따른 수화반응에 따라 변화하는데, 염해 저항성과 강도 특성은 다르게 변화한다. 본 연구에서는 재령이 28일에서 6개월로 증가하면서 변화하는 강도 및 염해 저항특성을 보통 콘크리트에 대하여 분석하였다. 이를 위해 3개의 물-시멘트비를 가진 일반 콘크리트에 대하여, 재령 28일과 6개월 수중양생을 수행하였으며, 강도, 염화물 확산계수, 통과전하량을 평가하였다. 재령이 28일에서 6개월로 증가하면서 강도변화는 135.3~138.3% 수준으로 증가하였으나, 염화물 확산계수의 경우 41.8%~51.1% 수준으로, 통과전하량의 경우 53.6%~70.0% 수준으로 감소하였다. 염화물 확산계수와 통과전하량의 경우는 비교적 비슷한 수준으로 감소하였는데, 두 결과는 전기장 내에서의 염화물 이동에 지배적이기 때문이다. 또한 강도의 변화비보다 염화물 확산계수 및 통과전하량의 변화비가 크게 증가하였는데, 이는 공극특성의 제곱에 비례하여 물질이동 특성이 변하기 때문이다.

• 한국건설순환자원학회논문집
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• 제10권3호
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• pp.307-313
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• 2022

본 연구에서는 3가지 수준의 물-시멘트 비, 상부 염수 농도, 피복 두께를 고려하여 반 전위와 영향인자들 간의 상관성을 분석하였다. 장기 부식 모니터링 결과 염수 농도 3.5, 7 %에서 초기에 모든 물-시멘트 비에서 임계부식전위(-350mV)에 근접하는 거동을 보였다. 통과 전하량 시험 결과 548일에서 모든 배합에서 'Moderate' 등급으로 개선된 통과 전하량이 평가되었다. 부식 영향인자와 반 전위 값 간의 상관성을 평가 하고자 다중 회귀분석을 수행하였는데, 염수 농도, 물-시멘트 비, 피복 두께 순으로 영향을 준 것으로 평가되었다. 반 전위와 통과 전하량간의 상관성 분석 결과는 0.9로 높은 수준의 결정계수를 보였으며, 통과 전하량과 반 전위 값 간에는 밀접한 상관성이 존재하는 것으로 판단된다.

• 한국구조물진단유지관리공학회 논문집
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• 제23권2호
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• pp.1-9
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• 2019

대표적인 콘크리트 혼화재료 중 하나인 고로슬래그 미분말을 혼입한 콘크리트는 잠재수경성에 의해 콘크리트의 장기 내구성능 및 역학적 성능이 향상된다. 본 연구에서는 3 가지 수준의 물-결합재 비(0.37, 0.42, 0.47) 및 고로슬래그 미분말 혼입률(0 %, 30 %, 50 %)을 고려하여 염해에 대한 내구성능 평가를 수행하였으며, 염화물 확산 거동(촉진 염화물 확산계수, 통과 전하량)을 예측하는 식을 도출하고 촉진 염화물 확산계수와 통과 전하량간의 상관관계를 평가하였다. 2년 양생조건 시 고로슬래그 미분말 혼입 콘크리트에서 OPC 콘크리트 대비 촉진 염화물 확산계수 평가 결과에서는 최대 28 %의 감소율을 통과 전하량 평가에서는 최대 29 %의 감소율을 나타냈다. 또한 물-결합재 비의 증감에 의한 영향을 OPC 콘크리트 보다 GGBFS 미분말 혼입 콘크리트에서 더 적게 받는 것으로 판단된다. 배합 특성 및 실험 결과를 바탕으로 촉진 염화물 확산계수 및 통과 전하량을 예측하는 식을 다중회귀분석을 통해 도출한 결과, 통과 전하량 예측식이 확산계수 예측식보다 높은 결정계수를 나타냈다.

• Computers and Concrete
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• 제13권1호
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• pp.17-30
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• 2014

This research presents the effect of various ground pozzolanic materials in blended cement concrete on the strength and chloride penetration resistance. An experimental investigation dealing with concrete incorporating ground fly ash (GFA), ground bottom ash (GBA) and ground rice husk ash (GRHA). The concretes were mixed by replacing each pozzolan to Ordinary Portland cement at levels of 0%, 10%, 20% and 40% by weight of binder. Three different water to cement ratios (0.35, 0.48 and 0.62) were used and type F superplasticizer was added to keep the required slump. Compressive strength and chloride permeability were determined at the ages of 28, 60, and 90 days. Furthermore, using this experimental database, linear and nonlinear multiple regression techniques were developed to construct a mathematical model of chloride permeability in concretes. Experimental results indicated that the incorporation of GFA, GBA and GRHA as a partial cement replacement significantly improved compressive strength and chloride penetration resistance. The chloride penetration of blended concrete continuously decreases with an increase in pozzolan content up to 40% of cement replacement and yields the highest reduction in the chloride permeability. Compressive strength of concretes incorporating with these pozzolans was obviously higher than those of the control concretes at all ages. In addition, the nonlinear technique gives a higher degree of accuracy than the linear regression based on statistical parameters and provides fairly reasonable absolute fraction of variance ($R^2$) of 0.974 and 0.960 for the charge passed and chloride penetration depth, respectively.

• 한국입자에어로졸학회지
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• 제14권1호
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• pp.17-24
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• 2018

Since the motion of the charged particle strongly depends on its charge characteristics, information on charge distributions of target particles is one of the important variables in aerosol research. In this study, charged distribution of atomized NaCl particles were measured using a Gerdien type ion counter. Two kinds of particle charging conditions were used in this study. First, atomized NaCl particles were passed through an aerosol neutralizer to have a Boltzmann charge distribution, and then its charge distribution was measured. In this case, the portion of uncharged particles was compared with the portion obtained from the Boltzmann charge distribution for verifying the suggested experimental method. Second, same experiment was conducted without the aerosol neutralizer to measure the charge distribution of atomized and un-neutralized NaCl particles. In the conclusion, the portion of uncharged, negatively charged and positively charged particles were 19%, 62% and 20%, respectively, for neutralized particles. The atomized particles, which was generated without the aerosol neutralizer, also had almost a zero charge state, but the standard deviation in charge distribution was larger than that of neutralized particles. The test method proposed in this study is expected to be used in various aerosol research fields because it can obtain simple information on the particle charge characteristics more easily and quickly than the existing test methods.

• 전기화학회지
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• 제1권1호
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• pp.8-13
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• 1998

This work presents the way how to evaluate the degree of reversibility of the discharging process undergone by the nickel hydroxide film cathodically deposited on pure nickel as a positive electrode for electrochemical capacitor using the combined cyclic voltammetry and potential drop method, supplemented by galvanostatic discharge and open-circuit potential transient methods. The time interval necessary just to establish the current reversal of anodic to cathodic direction from the moment just after applying the potential inversion of anodic to cathodic direction, was obtained on cyclic voltammogram. The cathodic charge density passed upon dropping the applied potential, was calculated on potentiostatic current density-time curve. Both the time interval and the cathodic charge density in magnitude can be regarded as being measures of the degree of reversibility of the discharging process undergone by the positive active material for supercapacitor, i.e. , the longer the time interval is, the lower is the degree of reversibility and the greater the cathodic charge density is, the higher is the degree of reversibility. From the applied potential dependences of the time interval and cathodic charge density, discharge at $0.42 V_{SCE}$ was determined to be the most reversible.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2008년도 하계학술발표대회 논문집
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• pp.288-293
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• 2008

The cooling load in winter is significant in many commercial buildings and hotels because of the usage of office equipments and the high efficiency of wall insulation. The development of a multi-heat pump that can cover heating and cooling simultaneously for each indoor unit is required. In this study, the performance of a multi-heat pump with 3-piping system was investigated as a function of refrigerant charge and its performance was analyzed in cooling mode, heating mode, and heat recovery mode. COP in the heating or cooling mode showed little dependence on refrigerant charge at overcharge conditions, while those were strongly dependent on refrigerant charge at undercharge conditions and outdoor inlet temperature. In the heat recovery mode, the performance of the system was very sensitive to charge amount at all conditions. Optimum charge amount in the heat recovery mode was 14% lower than that in the cooling mode at the standard condition because the refrigerant only passed the indoor units. It is required to store the excessive refrigerant charge in a storage tank to optimize the system performance at operating modes.

• 설비공학논문집
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• 제20권7호
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• pp.492-499
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• 2008

The cooling load in winter is significant in many commercial buildings and hotels because of the usage of office equipments and the high efficiency of wall insulation. The development of a multi-heat pump that can cover heating and cooling simultaneously for each indoor unit is required. In this study, the performance of a multi-heat pump with 3-piping system was investigated as a function of refrigerant charge and its performance was analyzed in cooling mode, heating mode, and heat recovery mode. COP in the heating or cooling mode showed little dependence on refrigerant charge at overcharge conditions, while those were strongly dependent on refrigerant charge at undercharge conditions and outdoor inlet temperature. In the heat recovery mode, the performance of the system was very sensitive to charge amount at all conditions. Optimum charge amount in the heat recovery mode was 14% lower than that in the cooling mode at the standard condition because the refrigerant only passed the indoor units. It is required to store the excessive refrigerant charge in a storage tank to optimize the system performance at operating modes.

• 한국구조물진단유지관리공학회 논문집
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• 제26권5호
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• pp.127-134
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• 2022

본 연구에서는 장기재령(4~6년)으로 양생된 플라이애시 콘크리트를 대상으로 촉진 염화물 이온 통과 시험을 수행하였다. 콘크리트 배합은 3수준의 물-결합재 비(0.37, 0.42, 0.47)와 2수준의 플라이애시 치환율(0, 30 %)을 가지고 있었으며, 시간 의존적으로 개선되는 통과 전하량을 정량적으로 분석하였다. 또한 실험결과를 GRU 알고리즘을 고려한 단별량 시계열 모델을 적용하여 학습하였으며, 그 예측값을 평가하였다. 통과전하량 실험 결과, 플라이애시 콘크리트는 물-결합재 비에 의한 통과 전하량의 변화가 재령이 증가함에 따라 점차 감소하였으며 OPC 콘크리트에 비하여 우수한 염해저항성을 나타내었다. 최종 평가일인 6년에서 플라이애시 콘크리트는 모든 물 결합재 비 조건에서 'Very low' 등급에 해당되는 통과 전하량이 평가되었지만, OPC 콘크리트의 경우 가장 높은 물-결합재 비를 갖는 조건에서 'Moderate' 등급을 나타내었다. 메인 알고리즘으로서 사용한 GRU 알고리즘은 시계열 데이터를 분석할 수 있고 연산 속도가 빠른 장점을 갖고 있다. 4개의 은닉층을 갖는 딥-러닝 모델이 고려되었으며 결과값은 실험값을 합리적으로 예측하고 있었다. 본 연구의 딥-러닝 모델은 단변량 시계열 특성만을 고려할 수 있는 한계점이 존재하지만 추가 연구를 통해 콘크리트의 강도 및 확산계수와 같은 다양한 특성을 고려할 수 있는 모델이 개발 중에 있다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1999년도 학회창립 10주년 기념 1999년도 가을 학술발표회 논문집
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• pp.341-344
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• 1999

In the case of the offshore concrete structures like the anchorage block of a suspension bridge of Kwangan Grand Road, there is a need of the concrete which has low heat of hydration and good resistance for sea-water attack. In this study, the blended super low heat cement which satisfies that requirement was developed and several tests were carried out. The concrete using the blended super low heat cement showed lower adiabatic temperature rise than 3$0^{\circ}C$ and good early strength. Also, its passed charge(coulomb) to resist chloride ion penetration was very low.