• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 춘계 학술발표회 논문집(II)
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• pp.549-552
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• 2006

Generally the ultra-high strength steel reinforced concrete has rich mix composition composed of high-strength type mineral admixtures and as a result of very low water-binder ratio(about under w/b=25%), it reveals ultra-high compressive strength(about over 100Mpa). Also, in order to obtain sufficient toughness after construction, we usually mix a large quantity steel fiber with ultra-high strength steel reinforced concrete therefore we must use proper mixer for workability. When we make the ultra-high strength steel reinforced concrete we need more long mixing time or much super-plasticizer than when we manufacture normal concrete. These bring about economical problems and performance deterioration. Therefore, in this study, in order to manufacture easily ultra-high strength steel reinforced concrete we develope a dedicated mixer for ultra-high strength steel reinforced concrete with high speed type. It carried out the examination for comparison between the dedicated and general type mixer, the analysis and counterplan of the point at issue when we manufacture ultra-high strength steel reinforced concrete by the dedicated mixer.

• International Journal of Concrete Structures and Materials
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• 제2권2호
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• pp.145-152
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• 2008

So far, there has been no study of the concrete to strengthen in the lining of the tunnels, except for the study of the stability of subgrade and the tunnel construction technologies. In the existing concrete work for tunnel lining, lots of problems happen due to the partial compaction and the material segregation after casting concrete. Accordingly, the aim of this study is to improve economic efficiency and secure durability through the improvement of the construction performance and quality of the concrete for the tunnel lining among the civil structures. Therefore, the compactability and strength properties of the High Flowing Self-Compacting Lining Concrete (HSLC) are evaluated to develop the mixing proportion for design construction technology of HSLC that can overcome the inner cavity due to the reduced flowability and unfilled packing, which has been reported as the problem in the existing lining concrete. The result of the evaluation shows that the ternary mix meets the regulations better than the binary mix. Consequently, it has been judged applicable to the cement for tunnel lining.

• Computers and Concrete
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• 제15권4호
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• pp.643-671
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• 2015

Chloride induced reinforcement corrosion is widely accepted to be the most frequent mechanism causing premature degradation of reinforced concrete members, whose economic and social consequences are growing up continuously. Prevention of these phenomena has a great importance in structural design, and modern Codes and Standards impose prescriptions concerning design details and concrete mix proportion for structures exposed to different external aggressive conditions, grouped in environmental classes. This paper focuses on reinforced concrete column section load carrying capacity degradation over time due to chloride induced steel pitting corrosion. The structural element is considered to be exposed to marine environment and the effects of corrosion are described by the time degradation of the axial-bending interaction diagram. Because chlorides ingress and consequent pitting corrosion propagation are both time-dependent mechanisms, the study adopts a time-variant predictive approach to evaluate residual strength of corroded reinforced concrete columns at different lifetimes. Corrosion initiation and propagation process is modelled by taking into account all the parameters, such as external environmental conditions, concrete mix proportion, concrete cover and so on, which influence the time evolution of the corrosion phenomenon and its effects on the residual strength of reinforced concrete columns sections.

• 콘크리트학회논문집
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• 제29권4호
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• pp.361-369
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• 2017

고성능 콘크리트의 개발로 인해 다양해지는 배합비에 따라, 콘크리트 초기강도 발현 시점을 예측할 수 있는 응결시점에 대한 관심이 높아지고 있다. 기존의 콘크리트 응결시간 측정을 위해 사용되고 있는 관입저항시험은 습식체가름을 실시한 모르타르를 이용한 간접적인 측정법으로, 현장 타설된 콘크리트의 정확한 응결시간을 나타내기 어렵다. 따라서 콘크리트에 직접 측정이 가능한 초음파 속도 측정법, 수화열 측정법, 전기 임피던스 측정법 등 다양한 비파괴 평가 기법들이 제안되고 있다. 본 연구에서는 수화 반응에 따른 시멘트계 재료 내부 전기전도성 변화를 측정하는 4-전극법을 이용하여 콘크리트의 전기 비저항 측정 기법을 제안하고자 한다. 다양한 배합비에 따라 시멘트 페이스트, 모르타르, 콘크리트의 전기 비저항 측정을 실시하였으며, 배합 후 24시간 측정결과로부터 초기 전기비저항 값과 전기비저항 상승시기를 측정 변수로 제안하였다. 또한, 관입 저항 시험에 따른 초결, 종결 시점과의 비교 분석을 통해 콘크리트 응결시점 평가를 위한 제안 기법의 적용 가능성을 확인하였다.

• 콘크리트학회논문집
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• 제14권1호
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• pp.67-75
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• 2002

콘크리트 구조물의 설계 덴 해석에 있어서나 구조물 처짐 제어에 있어서 가장 중요한 재료적 변수는 탄성계수이다. 일반적으로 탄성계수는 실용적 측면에서 측정이 용이한 단위중량과 압축강도만의 함수로써 간략하게 정의되고 있다. 그러나 이러한 회귀식들은 대부분 실험자료에 대한 평균적인 의미이므로 매우 많은 불확실성이 포함되어 있어 지금까지 제시된 많은 규준식 및 실험식들이 다소의 차이가 있다. Fig. 1에서와 같이 이러한 식들은 압축강도와 탄성계수사이의 큰 상관성이 있음을 잘 나타내고 있으나, 동일한 압축강도에서 탄성계수는 크게 분산된 값으로 측정됨을 알 수 있다. 본 연구에서는 고강도 콘크리트 영역에서 탄성계수에 미치는 배합변수들의 영향을 통계적 기법을 이용하여 분석하고 이를 통하여 동일한 압축강도에서 최대의 탄성계수를 얼기 위한 방안을 구명하였다.

• Geomechanics and Engineering
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• 제29권3호
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• pp.311-320
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• 2022

TBM concrete segment requires a higher level of material properties compared to general concrete structures due to difficulties in maintenance and uncertainty in ground conditions. In this regard, recently, as one of the methods to achieve enhancement effect on concrete strength, many researchers have been focusing on adding CNTs to concrete mixture. However, even CNTs do not compensate the weakness that concrete exhibits brittle behavior after cracking. Separately, over the past few decades, a number of studies have been conducted on fiber reinforced concrete which exhibits ductile behavior due to fibers bridging cracks. However, only limited studies have been conducted to employ the advantages of the both materials together. In this study, an experimental program has been conducted to investigate the effect of CNTs on the workability and the compressive behavior of PVA-ECC which exhibits ductile tensile behavior with well-distributed cracks even without a conventional rebar. In addition to the compression test, SEM analysis has been also conducted for detailed investigation in the microstructure. The variable was the CNTs mix ratio, which were set to 0.00, 0.25, and 0.50 wt.% to the binding materials. It was observed though the test results that as the CNTs mix ratio increased, the workability considerably decreased with the reduced slump and slump flow. From the compression test results, it was also investigated that the compressive behavior was improved since the compressive strength, the strain corresponding to the compressive strength, and the modulus of elasticity increased with an increase of CNTs mix ratio. The contents of this paper will be useful for relevant research areas such as fiber reinforced concrete with CNTs which might be applied for high performance TMB concrete segments.

• Structural Engineering and Mechanics
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• 제47권4호
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• pp.545-557
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• 2013

Disposal of construction wastes poses major challenge to the municipal administration in the developing countries. At the same time new developments in these countries are unscrupulously exploiting the natural resources. The sustainable development requires judicious and careful utilization of natural resources. In this context, reuse of construction and demolition waste can save the global natural resources to greater extent. In this work the bricks and concrete waste from construction sites were crushed to the desired sizes and mixed in various proportions to study its properties in the concrete both in fresh and hardened states. Six mixes of natural and recycled aggregates were used to make the coarse aggregates for the concrete. From each mix nine cylinders were cast, which were tested at 7,14 and 28 days. The properties of concrete with recycled aggregates were compared with the control mix having natural aggregates. The nominal ratio of cement sand and coarse aggregates were kept at 1:2:4 by weight for all mixes. The tests have shown that concrete with recycled aggregates made from old concrete and brick bats provide greater opportunities for reuse of construction wastes in concrete.

• 콘크리트학회지
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• 제7권3호
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• pp.149-155
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• 1995

무세골재 콘크리트에 석분을 혼입하므로써 얻을 수 있는 강도 증가효과를 조사하기 위하여 실험을 통한 연구를 수행하였다. 시멘트-골재의 비 1 : 6, 1 : 8 그리고 1 : 10 과 30~56% 사이의 여러 물 -시멘트 비를 배합설계시에 선정하였다. 작업하기 적당한 콘크리트를 얻기 위하여 필요에 따라 고유동화제를 시멘트중량의 1.5%사용하였으며, 석분을 혼입한무세골재 콘크리트의 경우 시멘트와 같은 중량의 석분을 혼입하였다. 여러 배합설계에 대한 압축강도와 인장강도 시험 결과를 비교분석하였다. 시험결과는 무세골재 콘크리트에 비하여 압축강도는 약 38%, 인장강도는 약 17%~72% 증가시킬 수 있음을 보여주고 있다.

• 콘크리트학회논문집
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• 제12권6호
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• pp.91-98
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• 2000

Porous concrete having continuous voids is gaining more interest as an ecological material. It has several useful functions such as water and air permeability, sound absorption, etc. Its strengths are considerably lower than those of conventional concrete due to the large and continuous voids in it. This study has been carried out to investigate the influence of mix factors and mixture proportion of aggregate on the strengths and water permeability of porous concrete. And it has been carried out to investigate the evaluation of void of porous concrete by the ultra-sonic pulse velocity. The results f this study are as follows: 1) The theoretical void ratio has greater influence than any other factor on the strengths and water permeability of porous concrete. And it is a little affected by the replacement proportion of silica-fume and mixture proportion of aggregate. 2) Because the coefficients of correlation between the void ratio and ultra-sonic pulse velocity were relatively high, it will be possible that the void ratio is predicted by the ultra-sonic pulse velocity.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2000년도 가을 학술발표회 논문집(II)
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• pp.961-966
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• 2000

It is difficult to change or remedy concrete structure after hardened. It is usual to evaluate the quality of hardened concrete using several test method. This study was performed to make fundamental data that could be used to evaluate the quality of hardened concrete. This study is to estimate mix proportion of hardened concrete. Each elements of concrete needed different estimation methods. First, the cement that handled by the most important compounds measured by XRF(X-ray fluorecence) machine with scanning Ca-K${\alpha}$. Second, the coarse aggregate that divided by maximum size measured by the area comparison method that starts from the assumption of uniform distribution. Third, the fine aggregate measured by the weight comparison method that needs several prerequsite constants which concerned cement hydration reaction. Fourth, the water content would be estimated by expert system that has data base of design data, the contents of above estimation results, the characteristics of concrete strength. As the result of the above research, some conclusions are as follows. The cement estimation method resulted by reliability of mean 96.7%, standard deviation 3.92. The area comparison method resulted by reliability of mean 95.3%, standard deviation 2.08. The weight comparison method resulted by reliability of mean 93.3%, standard deviation 3.35.