• Journal of the Korea Concrete Institute
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• v.19 no.2
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• pp.179-188
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• 2007

Recently, the concern on the receipt of poor ready-mixed concrete in the construction field and the durability of concrete has been increased. Based on the such background, a large number of measuring methods of water content for fresh concrete have been developed and enforced in a developed country. In this study, to investigate practicality for quality control of ready-mixed concrete among various water content measurement techniques, microwave range method, air meter method and capacitance measurement method as measuring methods of water content were selected. Then, it was evaluated estimating performance of water content according to the change of binder types, fine aggregate types, absorption ratio, water content and water-binder ratio in series I and II. Also, it was examined influence on error occurrence of water content according to change of properties of used materials in series III. Finally, based on this study, it was proposed fundamental data to utilize measurement technique of water content to quality control of ready-mixed concrete in construction field.

• Journal of the Korea Concrete Institute
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• v.25 no.4
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• pp.411-418
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• 2013

Recently, in order to reduce a damage of chloride attack and hydration heat in marine concrete structures, blended cement in mixing the marine concrete is widely used. Long term strength development is distinct in concrete with blended cement and it also has excellent resistance to chloride attack and reduction of hydration heat. However, blended cement has a characteristic of relatively low compressive strength in early age of 28 days. On the other hand, a high level of compressive strength is required in the Standard Specification for marine concrete mix design. Such concrete mix design satisfying Standard Specification is effective to chloride attack but disadvantageous for hydration heat reduction due to large quantity of binder. In this study, the material properties of marine concrete considering water-binder ratio and binder type are experimentally investigated. Through the research results, compressive strength in blended cement at the age of 56 days is similar although it has smaller compressive strength at the age of 28 days compared with result of OPC (ordinary portland cement). Even though blended cement has a large water-binder ratio and small unit of binder content, chloride ion diffusion coefficient is still small and hydration heat is also found to be reduced. For meeting the required compressive strength in Standard Specification for marine concrete at 28 days, the increased unit content of binder is needed but the increased hydration heat is also expected.

• Journal of the Korea Concrete Institute
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• v.29 no.4
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• pp.379-387
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• 2017

The objective of this study is to develop sustainable PVA fiber-reinforced cementitious composites (FRCCs) that could exhibit comparable strength level to normal PVA FRCCs with no recycled materials. To evaluate mechanical properties of the FRCCs, compressive, flexural and direct tensile tests were conducted. In addition to the test, to calculate amount of carbon dioxide ($CO_2$) emission at the stage of manufacturing the FRCCs, life cycle inventory data base (LCI DB) were referenced from domestic and Japan. From the test results, the mechanical properties such as compressive, flexural and direct tensile strengths were decreased as the replacement ratio of recycled materials increased. And it was determined that the amount of $CO_2$ emission was reduced for the specimens with higher water-binder ratio (W/B) and replacement ratios. It was also found that binder intensity ($B_i$) value was higher as replacement ratio of fly ash (FA) increased. This result means that larger amount of FA is need to deliver one unit of a given performance indicator (1 MPa of strength) of FRCCs compared to that of ordinary portland cement (OPC). As a result, it could be concluded that FRCCs with W/B 45% replaced by FA 25% and recycled sand (RS) 25% is desirable for both target performance and $CO_2$ emission.

• Journal of the Korea Institute of Building Construction
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• v.15 no.1
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• pp.1-7
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• 2015

The objective of this study is to develop a high-performance foamed concrete made with a new mixture proportioning as an alternative of autoclaved lightweight concrete (ALC) block. For the early-strength gain of the foamed concrete under an atmospheric curing condition, the binders and chemical agents were specially contrived as follows: 3% anhydrous gypsum was added to ordinary portland cement (OPC) in which $3CaO{\cdot}SiO_2$ content was controlled to be above 60%; and the content of polyethylene glycol alkylether in a polycarboxylate-based water-reducing agent was modified to be 28%. Using these binders and chemical agents, 11 mixes were prepared with the parameters of W/B ratio (30% to 20% in a interval of 2.5%) and unit binder content ($400kg/m^3$ to $650kg/m^3$ in a interval of $50kg/m^3$). The quality and availability of the mixed foamed concrete were examined according to the minimum requirements specified in the KS for ALC block and existed conventional foamed concrete. The measured properties satisfied the minimum requirement of KS for ALC block and proved that the developed high-performance foamed concrete had considerable potential for practical application.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.6
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• pp.52-58
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• 2017

Concrete made with ground granulated blast-furnace slag(GGBS) has many advantage, including improved durability, workability and economic benefits. GGBS concrete is that its strength development is considerably slower under standard $20^{\circ}C$ curing conditions than that of portland cement concrete, although the ultimate strength is higher for same water-binder ratio. GGBS is not therefore used in application where high early age strength is required. In this study, to overcome the limitation of the initial strength decrease due to the use of slag, the slag substitution rate was changed to 30% under the low temperature curing temperature condition and the slag used concrete composition with the same or higher strength performance as OPC(Ordinary Portland Cement).

• Proceedings of the Korea Water Resources Association Conference
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• 2020.06a
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• pp.360-360
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• 2020

조립식 빗물침투형 저류블록은 우수유출 저감시설로, 황토 및 친환경 무기질 결합재를 이용하여 제작한 고강도 투수성 블록의 적층 및 요철에 의한 끼움식 조립에 의해 형성된 공간에 빗물을 저류하고, 저장된 빗물은 시간이 지남에 따라 지반으로 침투시키는 우수유출 저감용 빗물관리시설로, 집중강우 시 유출수가 발생하는 해당지역에 분산식으로 설치하여 국지적 호우 발생에 대처할 수 있으며, 지속적인 침투를 통한 지하수위 확보 및 가뭄현상의 저감은 물론, 미기후 조성과 건전한 물순환 구조 형성에 이바지하는 빗물관리기술이다. 본 기술은 집중형 대규모 빗물저류조의 적용상의 문제점과 단순저류의 한계성을 극복하고, 기존 침투시설의 낮은 침투능을 증대시키고자 저류기능과 침투기능을 동시에 확보하여 집중호우시 빠른 침투저류능을 향상시킨 조립식 빗물침투형 저류시설이다. 보다 구체적으로는 집중강우에 대한 방재적 측면과 함께 가뭄으로 발생하는 지하수위 저하 등에 친환경적으로 대응하기 위한 복합적인 빗물관리 기술로서, 빗물 유출저감과 함께 물순환 회복 및 저영향개발을 위한 각 지자체의 지침과도 부합될 수 있다. 또한, 콘크리트 제품의 환경적 문제점과 플라스틱 제품의 낮은 물성을 극복하였고, 시공 시에는 보다 현장상황에 맞게 가변적 형태로 적용이 가능한 단순조립 적층공법으로 공기단축에 탁월한 장점이 있으며, 유지관리 시에는 별도의 동력이 요구되지 않는 형태로 개발하였다. 조립식 빗물침투저류블록의 구조체를 이루는 단위 블록유닛은 투수성 소재로 제작되며, 상하부가 개방되어 있고 사각형의 내부에 힘을 받는 격벽과 전후벽이 상호 대응되는 요철로 형성되어 있으며, 단위블록 유닛 다수개가 수직수평으로 연속적으로 조립되어 규모의 제한, 형태의 제한이 없는 구조물 형성이 가능하다. 본 구조체의 저류공극율은 80%이상 확보 가능하며, 또한 블록자체의 투수율이 0.83mm/sec로서 순모래나 순자갈의 포화투수계수보다 투수율이 높아 침투저류 효율성이 높으며 시공 후 상부 토지는 자유롭게 활용 가능하다. 본 조립식 빗물 침투형 저류블록을 이용하여 저영향개발 계획, 우수유출 저감대책 수립, 빗물관리시설 계획시 기존의 시설들에 비하여 경제적, 효율적인 설계가 가능하다.

• Journal of the Korean Recycled Construction Resources Institute
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• v.1 no.2
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• pp.114-119
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• 2013

The present study tested 5 concrete mixes to develop reliable mixing proportions for the sustainable alkali-activated(AA) foamed concrete as a thermal insulation material for the floor heating system of buildings. The AA binder used was composed of 73.5% ground granulated blast-furnace slag, 15% fly ash, 5% calcium hydroxide, and 6.5% sodium silicate. As a main variable, the unit binder content varied from $325kg/m^3$ to $425kg/m^3$ at a space of $25kg/m^3$. The test results revealed that AA foamed concrete has considerable potential for practical applications when the unit binder content is close to $375kg/m^3$, which achieves the minimum quality requirements specified in KS F 4039 and ensures economic efficiency. In addition, lifecycle assessment demonstrated the reduction in the environmental impact profiles of all specimens relative to typical ordinary portland cement foamed concrete as follows: 99% for photochemical oxidation potential, 87~89% for global warming potential, 78~82% for abiotic depletion, and 70~75% for both acidification potential and human toxicity.

• Journal of the Korea Concrete Institute
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• v.19 no.3
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• pp.377-383
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• 2007

In recent years the field application of high performance concrete has been increased to improve the quality and reliability of concrete structures. The mix design of the high performance concrete includes the 2 set-off mixture theory of mortar and coarse aggregate and that of paste and aggregate. The 2 set-off mixture theory of mortar and coarse aggregate has a problem of having to determine its value through repeated experiments in applying the rheological characteristics of mortar. The 2 set-off mixture theory of paste and aggregate has never been applied to high performance concrete since it doesn't take into account the relationship between optimum fine aggregate ratio and unit volume of powder nor does it consider the critical aggregate volume ratio. As the mixture theory of these high performance concretes, unlike that of general concrete, focuses on flowability and charge-ability, it does not consider intensity features in mix design also, the unit quantity of the materials used is determined by trial and error method in the same way as general concrete. This study is designed to reduce the frequency of trial and error by accurately calculating the optimum fine aggregate ratio, which makes it possible to minimize the aperture of aggregate in use by introducing the maximum density theory to the mix design of high performance concrete. Also, it is intended to propose a simple and reasonable mix design for high performance concrete meeting the requirements for both intensity and flowability. The mix design proposed in this study may reduce trial and error and conveniently produce high performance concrete which has self-chargeability by using more than the minimum unit volume of powder and optimum fine aggregate with minimum porosity.

• Journal of the Korea Institute of Building Construction
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• v.18 no.3
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• pp.259-266
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• 2018

In recent years, the early strength of concrete is important in order to shorten the time of form removal at the construction site. The purpose of this study is to analyze the moment of form removal as investigating the amount of cement contents and the physical properties and strength of the concrete according to types of admixture in the curing temperature of $10^{\circ}C$ for concrete of 21 to 27 MPa. As a result, it was found that compressive strength of concrete could not be secured 5 MPa by 36 hours even if the amount of cement contents were increased to $360kg/m^3$ with plain admixture. Also, it was confirmed that the strength improvement rate was excellent when using the accelerating agent with polycarboxylic acid type, and the moment of compressive strength of 5 MPa was estimated at 30 hours.

• Journal of the Korean Recycled Construction Resources Institute
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• v.6 no.1
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• pp.72-79
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• 2011

This study is performed to analyze the effects of CASB by applying the superplasticizer combined CASB on the ultra high strength mortar and concrete that uses different mineral admixture depending on whether the silica fume was used and the results are summarized below. From the characteristics of Fresh mortar and concrete, the fluidity was lower in B2-CASB than B2-PC from the mixing of CASB and based on the viscosity of the mortar and concrete in the binary proportion but in the ternary proportion, B3-CASB showed a larger fluidity than B3-PC because of a reduction in the restriction level due to the effects of an improvement of particle size distribution. The compression strength was higher in ternary proportion than in binary proportion and higher in CASB than in PC from the characteristics of hardening mortar and concrete and this is analyzed as a result of increased minuteness from the calcium silicate hydrates produced from the pozzolan reaction of a mineral admixture, SF, and also the charging effects of capillary pore of CASB. Overall, when using the nanomaterial, CASB in combination with a superplasticizer, the fluidity and the strength aspects of the ternary proportion of ultra high strength mortar and concrete with silica fume may be improved to a higher quality.