• Magazine of the Korea Concrete Institute
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• v.10 no.1
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• pp.101-108
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• 1998

시멘트 대체재로 사용하는 플라이애쉬(0, 10 , 30 ,50 %)를 혼입한 콘크리트의강도발현을 관찰하기 위해 각각 21$^{\circ}C$에서 수중양생과 85$^{\circ}C$에서 증기양생방법을 채택하여 실험하였다. 수중양생한 보통 콘크리트는 플라이애쉬 혼입량이 증가할수록 조기재령에서는 낮게 강도발현을 하였으나. 28일 압축강도를 기준으로 하여 물.시멘트비를 변화한 배합비(결합재량 증가)의 실험결과는 조기강도발현이 향상되었다. 특히 플라이애쉬를 30%혼입한 콘크리트는 우수하게 강도발현을 하였다. 그리고 동일한 28일 압축강도를 갖는 배합비(결합재량 증가)에서 증기양생한 플라이애쉬콘크리트는 보통콘크리트보다 강도발현이 비슷하거나 향상되었으며, 양생온도는 플라이애쉬콘크리트의 강도발현에 많은 영향을 미치는 것으로 관찰되었다.

• Journal of the Korea Concrete Institute
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• v.21 no.4
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• pp.441-447
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• 2009

This paper presents a detailed experimental study on the sulfate resistance of specimens made with portland cement exposed to sulfate attack. The mortar specimens were immersed in a 5% sodium sulfate solution for 360 days and regularly monitored for visual damage, compressive strength loss and expansion. In addition, at the end of 360 days, the products of sulfate attack and the mechanism of attack were investigated through X-ray diffraction, TG&DSC and scanning electron microscopy. The test results indicated that the sulfate deterioration data was ordinary portland cement > sulfate resistance portland cement > low heat portland cement. The microstructural studies indicated that the main reaction product of deterioration of the mortar specimens was the formation of ettringite, gypsum and thaumasite due to sulfate attack. For portland cement matrices, a low heat cement matrix containing the lowest C3A and silicate ratio (C/S) was beneficient against the sulfate attack.

• Magazine of the Korea Concrete Institute
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• v.10 no.5
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• pp.89-100
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• 1998

본 연구는 양생온도이력이 콘크리트 강도에미치는 영향을 평가하기 위한 것으로 물 시멘트비가 60%, 45%, 26%인 3종류의 콘크리트에대하여 5$^{\circ}C$부터 5$0^{\circ}C$까지의 항온양생과 초기재령에 고온도이력을 변수로 한 변동온도양생을 실시한 공시체의 압축강도를 측정하였다. 또한 그 실험결과에 강도평가 방법의 하나인 Maturity 개념을 도입하여 강도평가에 미치는 재령, w/c, 온도이력 등에 대한 영향을 평가하였다. 항온양생 실험결과에 따르면 물시멘트비가 낮을수록 초기재령에서의 강도발현은 높게 나타나며 양생온도 5$0^{\circ}C$인 경우를 제외하고 재령7일까지의 강도발현은 양생온도가 높을수록 크게 나타나고 있다. 한편, 변동온도양생실험결과에 의하면 초기재령에서 고온양생한 콘크리트의 강도발현은 물시멘트비의 영향을 크게 받으며, 1주 이후의 양생온도가 강도발현에 미치는 영향은 1주까지의 고온도이력에 대한 영향에 비교해 2차적이다. 기존의 Maturity개념인 Saul-Bergstrom의 함수와 Ooi의 함수를 가지고 항온 및 변동온도 양생실험결과를 분석한 결과, 전체적으로 Saul-Bergstrom식에 의한 경우가 실험값과의 차이가 작게 나타났으나 두 식 모두 Maturity 가 큰 경우에는 계산에 의한 값이 실험에 의한 값보다 크게 나타나고 있어 장기 재령시 강도평가는 한계강도 개념을 고려한 새로운 Matruity함수를 제안할 필요가 있다.

• Journal of the Korea Concrete Institute
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• v.17 no.1 s.85
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• pp.77-84
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• 2005

The steel slag, a by-product which is produced by refining pig iron during the manufacture of steel, is mainly used as road materials after aging. It is necessary to age steel slag for long time in air because the reaction with water and free-CaO in steel slag could make the expansion of volume. This problem prevents steel slag from being used as aggregate for concrete. However, steel slag used in this study was controled by a air-jet method which rapidly cools substance melted at a high temperature. The rapidly-chilled method would prevent from generation of free-CaO in steel slag. This study dealt with the influence of the using rate of rapidly-chilled steel slag on flow, dosage of SP, W/C ratio, and strength of mortar by statistical experimental design. Also, the results of this experiment were approved by statistical analysis methods, such as analysis of variance and F-testing. As results of F-testing, this paper proved at $1\%$ level of significance that the more the using rate of rapidly-chilled steel slag increased, the more this affected the enhancement of flow, the decrease of dosage of SP and W/C ratio, and the development of compressive strength. Also, considering the fluidity and compressive strength of mortar, it is desirable to use $75\%$ of rapidly-chilled steel slag for river sand.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.9 no.2
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• pp.81-86
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• 2011

Polymer-modified cement is the composite material made by partially replacing and strengthening the cement hydrate binders of conventional mortar with polymeric modifiers such as polymer latexes and redispersible polymeric modifiers. It is known that the addition of polymer to cement mortar leads to improved quality, which would be expected to have a high chemical resistance. Therefore, the purpose of this study is to identify the improved chemical resistance, such as low permeability and low ion diffusivity, of the polymer-modified cement as a solidification agent for the radwaste. First, polymer-modified cement specimens by latex modification were prepared according to the polymer content from 0% to 30% to select the optimized polymer content. At those specimens, the water-to-cement (W/C) ratio was maintained to 33% and 50% respectively. After the much curing time, the structural integrity of specimens was evaluated through the compressive strength test and the porosity evaluation by the water immersion method. From the results, 10% of the polymer content at 33% of the W/C ratio was shown to have the most improved quality. Finally, the leaching test referredfrom ANS 16.1 for the specimens having the most improved quality was conducted. Dedicated specimens for the leaching test were then mixed with radioisotopes of $^{60}Co$ and $^{137}Cs$ at the specimen preparation.

• Journal of the Korean Recycled Construction Resources Institute
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• v.5 no.2
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• pp.113-120
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• 2017

HCP(Half Cell Potential) method has been widely used since it is recognized as a efficient NDT(Non Destructive Technique) for corrosion detection. This work is for an evaluation of relation between corrosion amount and measured HCP in dried condition through ICM(Impressed Current Method) for accelerating corrosion. For the work, cement mortar specimens with three w/c ratios and four cover depths are prepared, and corrosion test based on ICM is performed for 6 hours, 18 hour, and 42 hours with constant 20V of electrical charge, respectively. From the test, corrosion amount increases with reduced cover depth, increasing w/c ratio, and extended corrosion period, where corrosion amount is evaluated to linearly increases with measured HCP in dried condition. In order to evaluate corrosion amount through measured HCP, the measured HCP level is firstly determined and then corrosion amount is to be compared with measured HCP, which is evaluated to be more reasonable with higher C.O.V.

• Proceedings of the Korean Institute of Industrial Safety Conference
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• 1998.11a
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• pp.321-326
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• 1998

폐콘크리트양은 건설폐기물 발생량의 약 50%정도인 연간 약 500만톤 이상으로 추정하고 있다. 따라서, 건설폐기물인 폐콘크리트에 대한 적절한 기술적 처리와 재활용 시스템이 구축된다면 도로포장 및 기타 포장 하층노반재료, 재생 입도조정쇄석, 건축물의 기초재, 토목 구조물의 기초재, 공작물의 되메우기 재료 등으로 활용될 수 있어 폐기되어버릴 단순한 쓰레기가 아니라 오히려 재활용 용도를 적극 개발하여야 할 중요한 자원이라고 볼 수 있다. 본 연구의 목적은 여러가지 건설 폐기물 중에서도 재활용 가능성이 높으며 구조물 해체시 다량으로 얻어지는 폐콘크리트를 대상으로 건설공사에 재이용하기 위해 폐콘크리트 골재를 사용한 재생콘크리트의 공학적 특성을 실험을 통해 검토하고자 하는 것이다. (중략)

• Journal of the Korea Concrete Institute
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• v.17 no.5 s.89
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• pp.709-716
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• 2005

The objective of this study is to develop a high ductile fiber reinforced mortar, ECC(Engineered Cementitious Composite) with using raw material commercially available in Korea. A single fiber pullout test and a wedge splitting test were employed to measure the bond properties in a matrix and the fracture toughness of mortar matrix respectively, which are used for designing mix proportion suitable for achieving strain-hardening behavior at a composite level. Test results showed that the properties tended to increase with decreasing water-cement ratio. A high ductile fiber reinforced mortar has been developed by employing micromechanics-based design procedure. Micromechanical analysis was initially peformed to properly select water-cement ratio, and then basic mixture proportion range was determined based on workability considerations, including desirable fiber dispersion without segregation. Subsequent direct tensile tests were performed on the composites with W/C's of 47.5% and 60% at 28 days that the fiber reinforced mortar exhibited high ductile uniaxial tension property, represented by a maximum strain capacity of 2.2%, which is around 100 times the strain capacity of normal concrete. Also, compressive tests were performed to examine high ductile fiber reinforced mortar under the compression. The test results showed that the measured value of compressive strength was from 26MPa to 34 MPa which comes under the strength of normal concrete at 28 days.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.6
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• pp.80-87
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• 2015

In this study, several properties of mortars made with calcium aluminate cement (CAC) such as hydrated products, strength characteristics, absorption, surface electric resistivity and chloride ions penetration resistance were experimentally investigated. The properties of CAC mortars were compared to those of ordinary portland cement (OPC) mortars. From the test results, it was found that the main hydrated products for CAC mortars were of $C_2AH_8$ and $CAH_{10}$, while CH, ettringite and calcite for OPC mortars. The surface electric resistivity and chloride ions penetration resistance of CAC mortars were significantly beneficial compared to those of OPC mortars. However, it should be noted that the absorption properties of CAC mortars were negatively examined. Thus, it needs to have more study for the improvement of surface absorption of CAC matrices. In addition, the combined mixture of CAC and OPC were ineffective to improve some performances of mortars.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.569-572
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• 2008

This study carried out to evaluate the quality deviation according to Premixed and Non-Premixed cement for normal and high strength concrete using blast furnace slag and fly ash. The results of experiment are founded that concrete using premixed cement have more performance than non-premixed cement at a point of view for the quality deviations both strength and Chloride ion diffusion. Therefore, it is desirable that premixed cement should be used to decrease strength deviation in high strength concrete and durability deviation in normal strength concrete.