• Journal of the Korean Recycled Construction Resources Institute
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• v.5 no.4
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• pp.353-358
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• 2017

The aim of this research is providing a fundamental idea on reducing viscosity of high performance cementitous materials. In rheological aspect, to determine the fluidity of the cementitious materials, both yield stress and viscosity should be controlled. For the high performance cementitious materials with low water-to-binder ratio and high volume fraction, it was difficult to reduce the viscosity with superplasticizer while reducing yield stress was relatively easy. Hence, in this research, with the goal of reducing viscosity of the cementitious materials, both ways of reducing viscosity were suggested: achieving proper combination of powder conditions, and adding low-viscosity typed water reducer. First, by replacing various byproduct powders, specifically, raw coal ash and wasted limestone powder showed favorable results on reducing viscosity of the cement paste. Regarding the low viscosity typed superplasticizer, it showed a good performance on reducing viscosity comparing with generic superplasticizer. Therefore, based on the results of this research, it is expected to provide a fundamental idea on reducing viscosity of cementitious materials by various methods.

• Journal of the Korea Concrete Institute
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• v.12 no.5
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• pp.111-120
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• 2000

In case of constructing concrete structure under water, generally concrete mixed with antiwashout admixture, high range water reducer, or AE-water reducing agent etc has been manufactured to ensure the quality of antiwashout underwater concrete because of being difficulty in ascertaining construction situation by the naked eye. The properties of high quality antiwashout underwater concrete that were aimed at affluent fluidity, workability and the compressive strength of 450 kgf/$\textrm{cm}^2$ at 28 ages using two types of blended cements are following as;(1) Setting time of antiwashout underwater concretes using blended cements was more greatly delayed than that of control concrete, however, was satisfied with criteria value of "Quality standard specification of antiwashout admixture for concrete".(2) As a test results of slump flow, efflux time and box elevation of head, it was found that workability of high quality antiwashout underwater concrete was improved. (3) Heat evolution amount of OPC was 1.5 times as high as that of two types of bended cements in 72 hours. (4) Suspended solids of antiwashout underwater concrete using blended cements was more than that of control concrete, also compressive strength of high quality antiwashout underwater concrete was very low in early age, but was better than that of control concrete as to increasing ages.

• Proceedings of the Korea Concrete Institute Conference
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• 1993.04a
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• pp.79-88
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• 1993

The purpose of this study is to provide a firm base for the quality improvement of high strength concrete and the development of ultra high strength concrete as well as enviromental con-servation and utilization of byproducts from industrial processing such as Fly ash and Silica fume. A comprehensive experimental study was performed to investigate the effects on the quality improvement of high strength concrete using mineral admixtures. As results, 400~500kg/$\textrm{cm}^2$ compressive strength and excellent flowability can be obtained if fly ash is replaced with cement in the range of 305. In case of using powder type silica fume, 600~700 kg/$\textrm{cm}^2$ compressive strength is showed and 600~800kg/$\textrm{cm}^2$ compressive strength cam be obtained with liquid type silica fume. But it is necessary to increase dosage of high range water reducer for flowability using powder type silica fume. Especially, higher strength concrete cam be obtained when maximum size of coarse aggregate is lower than 25mm.

• Steel and Composite Structures
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• v.29 no.1
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• pp.67-75
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• 2018

High performance concrete (HPC) depends on various parameters such as the type of cement, aggregate and water reducer amount. Generally, the ready concrete company in various regions according to the requirements and costs, mix design of concrete as well as type of cement, aggregates, and, amount of other components will vary as a result of moment decisions or dynamic optimization, though the ideal conditions will be more applicable for the design of mix proportion of concrete. This study aimed to apply dynamic optimization for mix design of HPC; consequently, the objective function, decision variables, input and output variables and constraints are defined and also the proposed dynamic optimization model is validated by experimental results. Results indicate that dynamic optimization objective function can be defined in such a way that the compressive strength or performance of all constraints is simultaneously examined, so changing any of the variables at each step of the process input and output data changes the dynamic of the process which makes concrete mix design formidable.

• Magazine of the Korea Concrete Institute
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• v.5 no.1
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• pp.165-173
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• 1993

본 연구는 고강도 콘크리트 실용화의 일환으로 국내에서 시판되고 있는 고성능 감수제의 품질성능을 평가하기 위한 것이다. 이러한 연구를 위하여 8종류의 고성능 감수제를 대상으로 첨가량에 따른 특성을 비교하였다. 또한 경시변화에 따른 특성을 비교, 분석하기 위하여 슬럼프, 공기량 그리고 압축강도비를 측정하였다. 이 때 고성능 감수제의 품질성능 평가 규준는 JASS 5T-402 규준에 따라 실시하였다. 실험결과 국내에서 시판되는 고성능 감수제는 공기량, 앞축강도비에 대해서는 모두 만족하였지만 슬럼프 경시 저하량은 DA를 제외한 모든 고성능 감수제가 규준치를 초과하였다. 따라서 현장에서 고강도콘크리트를 생산할 경우 배합방법이나 첨가방법을 개선하여 시공성을 확보하는 방안이 필요할 것이다.

• Proceedings of the Korea Concrete Institute Conference
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• 1995.10a
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• pp.235-240
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• 1995

A 36 stories high multi-use building was designed with the specified concrete strength range of 300~400kg/$\textrm{cm}^2$ On the ground of the concept of compressive strength, adequate mix designing for the concrete, which has the target strength range of 390-520kg/$\textrm{cm}^2$, was carried out to provide enough strength margin. And with due regard to the workability and transportation time, the slump and slump flow ranged 16~21cm and 30~45cm respectively, maintaining these properties up to 2-hours from the beginning of the mix. The high-range water reducer is incorporated into the mix as a admixture. The building construction is controlled satisfactorily, so far. The actual average 28-day compressive strength is 370kg/$\textrm{cm}^2$, the standard deviation is 28kg/$\textrm{cm}^2$ and the coefficient of variation is 7.6% for concrete of 300kg/$\textrm{cm}^2$ specified strength.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.05a
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• pp.107-113
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• 2003

The rheology properties of cement paste with variation of quantity and type of mineral admixture were investigated. The rheology of the paste was assessed by using a HAAKE Rotovisco(RT 20) rheometer having cylindrical serrate spindle. The results were as follows: The viscosity and the yield stress of cement paste were decreased by the only replacement of 10% BFS(blast furnace slag) or the only replacement of 30% FA(fly ash), whereas SF(silica fume) increased them as the replacement quantity was increased. Increasing the dosage of HRWR(high-range water reducer), the rheology properties were improved significantly in cement paste with the replacement of SF. In addition, rheology properties of two ingredient blended pastes, such as BFS(20%)-SF(5%), FA(20%)-SF(5%), were improved more than those of three ingredient blended paste, BFS(20%)-FA(20%)-SF(5%).

• Proceedings of the Korea Concrete Institute Conference
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• 1996.10a
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• pp.260-265
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• 1996

Polyproplyene Fibers have many advantages such as light weight, low cost, chemical stability and duragbility. It has been reported that polypropylene fiber can increase the toughness of concrete and the resistance to crack formation. This study has been performed to investigate the dirability related properties such as permeability and diffusivity of polypropylene fiber reinforced concrete. The permeability and diffusivity were measured with GWT, Poroscope, and electrical conductivity of concrete. From the test result, it is found that the addition of the polypropylene fiber improved the permeability and diffusivity of concrete, when the workability reduction was corrected by water reducer. The relationships between the permeability and diffusivity, and other properties of polypropylene fiber reinforced concrete showed that the tesst results are interrelated each other.

• Nuclear Engineering and Technology
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• v.42 no.1
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• pp.73-78
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• 2010

The suppression of molten salt vaporization is one of the key technical issues in the electrolytic reduction process developed for recycling spent nuclear fuel from light-water reactors Since the Hertz-Langmuir relation previously applied to molten salt vaporization is valid only for vaporization into a vacuum, a diffusion model was derived to quantitatively assess the vaporization of LiCl, $Li_2O$ and Li from an electrolytic reducer operating under atmospheric pressure. Vaporization rates as a function of operation variables were calculated and shown to be in reasonable agreement with the experimental data obtained from thermogravimetry.

• International Journal of Concrete Structures and Materials
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• v.19 no.1E
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• pp.41-48
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• 2007

Addition of latex to concrete is known to increase its durability and permeability. The purpose of this study is to analyze air void systems in latex-modified concretes using a reasonable and objective method of image analysis with such experimental variables as water-cement (w/c) ratios, latex contents (0%, 15%) and cement types (ordinary portland cement (OPC), high-early strength (HES) cement and very-early strength (VES) cement). The results are analyzed by spacing factor, air volume (content) after hardening, air void distribution and structure. Additionally, air void systems and permeability of latex-modified concrete (LMC) are compared by a correlation analysis. The results are as follows. The LMC of the same w/c ratio showed better air entraining (AE) effect than OPC with AE water reducer. The VES-LMC showed that the quantity of entrained air below $100{\mu}m$ increased more than four times. For the case of HES-LMC, microscopic entrained air between the range of 50 to $500{\mu}m$ increased greater than 7 times even in the absence of anti-foamer. Although spacing factor was measured rather low, the permeability of latex-modified concrete was good. It is construed that air void system does not have a considerable effect on the property of latex-modified concrete, but latex film (membrane) has a definite influence on the durability of LMC.