• Proceedings of the Korea Concrete Institute Conference
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• 1997.10a
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• pp.456-461
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• 1997

The purpose of this experimental study are to produce a durable concrete and to investigate the various factors that can deteriorate the concrete when freezing and thawing activity. Among the various factors that can influence the frost resistance of concrete, this study examined mainly the relationship of the frost resistance with the water-cement ratio, admixture and admixture replacement ratio and propose the available water-cement ratio, admixture and admixture replacement ratio.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.2
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• pp.529-536
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• 2014

Physical characteristics of cement-admixed clay such as water content, specific gravity, unit weight and void ratio are main factors for strength, compressibility and prediction of consolidation behavior. In the past, the physical characteristics of admixed soils could be understanded through complex laboratory tests and field survey after construction. In this study, the tests were performed with conditions such as clay water contents 0%-170%, cement contents 5%-25% and curing period 3-90days after that analyzed for changes which are water content, specific gravity unit weight and void ratio of admixed soils. A prediction of properties through mechanical relationships with clay in situ water content, cement content and curing period could be proposed using the test results. The prediction equation of void ratio of admixed soils was derived using void ratio equation in geotechnical engineering and compared with test results of bangkok clay and then this study could be verified.

• Journal of the Korea Concrete Institute
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• v.17 no.2 s.86
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• pp.293-302
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• 2005

This study describes data from determination of the optimum mix proportion and site application of the mass concrete placed in bottom slab and side wall having a large depth and section as main structures of LNG in-ground tank. This concrete requires low heat hydration, excellent balance between workability and consistency because concreting work of LNG in-ground tank is usually classified by under-pumping, adaptation of longer vertical and horizontal pumping line than ordinary pumping condition. For this purpose, low heat Portland cement and lime stone powder as cementitious materials are selected and design factors including unit cement and water content, water-binder ratio, fine aggregate ratio and adiabatic temperature rising are tested in the laboratory and batch plant. As experimental results, the optimum unit cement and water content are selected under $270kg/m^3$ and $l55{\~}l60 kg/m^3$ separately to control adiabatic temperature rising below $30^{\circ}C$ and to improve properties of the fresh and hardened concrete. Also, considering test results of the confined water ratio($\beta$p) and deformable coefficient(Ep), $30\%$ of lime stone powder by cement weight is selected as the optimum replacement ratio. After mix proportions of 5cases are tested and compared the adiabatic temperature rising($Q^{\infty}$, r), tensile and compressive strength, modulus of elasticity, teases satisfied with the required performances are chosen as the optimum mix design proportions of the side wall and bottom slab concrete. $Q^{\infty}$ and r are proved smaller than those of another project. Before application in the site, properties of the fresh concrete and actual mixing time by its ampere load are checked in the batch plant. Based on the results of this study, the optimum mix proportions of the massive concrete are applied successfully to the bottom slab and side wall in LNG in-ground tank.

• Computers and Concrete
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• v.31 no.4
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• pp.359-370
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• 2023

Slime is produced by excavation during the installation of embedded piles, and it tends to mix with the cement paste injected into the pile shafts. The objective of this study is to investigate the strength and stiffness characteristics of cement pasteslime mixtures. Mixtures with different slime ratios are prepared and cured for 28 days. Uniaxial compression tests and elastic wave measurements are conducted to obtain the static and dynamic properties, respectively. The uniaxial compressive strengths and static elastic moduli of the mixtures are evaluated according to the curing period, slime ratio, and water-cement ratio. In addition, dynamic properties, e.g., the constrained, shear, and elastic moduli, are estimated from the compressional and shear wave velocities. The experimental results show that the static and dynamic properties increase under an increase in the curing period but decrease under an increase in the slime and water-cement ratios. The cement paste-slime mixtures show several exponential relationships between their static and dynamic properties, depending on the slime ratio. The bearing mechanisms of embedded piles can be better understood by examining the strength and stiffness characteristics of cement paste-slime mixtures.

• Journal of the Korean Recycled Construction Resources Institute
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• v.3 no.2
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• pp.132-139
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• 2015

In this study, the different unit cement content by the ratio of water absorption and water-cement ratio are applied to examine the properties of the concrete used the aggregate recycled by the crushing treatment. According to the experimental results, in the mix of low strength and high water-cement ratio, both of the compressive strength is almost equal in the concrete using the recycled aggregate by the crushing treatment and the concrete using broken stones. It means that the recycled aggregate has the low effect of the amount of bonded mortar. But, in the mix of high strength and low water-cement ratio, the concrete using the recycled aggregate by the crushing treatment has 40% less of the compressive strength than that using broken stones by the effect of the amount of bonded mortar. On the other hand, after 8 weeks, the dry shrinkage of the recycled aggregate with 7% of the ratio of water absorption doubles that of the broken stones with 1% ($-350{\times}10^{-6}$), in other words $-700{\times}10^{-6}$. Thus, the dry shrinkage should be prior to any other conditions in recycling waste concrete for the aggregate for concrete. When the recycled aggregate with 3% of the ratio of water absorption is used, the compressive strength of the rich mix concrete ($450kg/m^3$ of the unit cement content) is equivalent to that of the concrete using broken stones, while in using the recycled aggregate with 7% of the ratio of water absorption, the rich mix concrete has 7% lower compressive strength than the concrete using broken stones. But, the compressive strength of the ordinary mix concrete ($350kg/m^3$ of the unit cement content) is far lower than that using broken stones.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.8 no.2
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• pp.1-8
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• 2012

The G-class cement is usually used for geothermal well grouting to protect a steel casing which is equipped in a geothermal well to transfer geothermal water from deep subsurface to ground surface. In geothermal grouting process, obtaining appropriate fluidity is extremely important in order to fill cement grout flawlessly. In this paper, a series of the V-funnel and Slump Flow test was performed on both of the Portland cement and the G-class cement in order to compare fluidity and filling ability of those kind of cements. In the result of V-funnel test, the fluidity of G-class cement was evaluated much better than the Portland cement at the water/cement ratio of 0.8. In the case of Slump Flow test, the fluidity of G- class cement was estimated slightly better than the Portland cement at both the water/cement ratio of 0.55 and 0.8. Even though the initial fluidity and filling ability of G-class cement were relatively higher than the Portland cement, the results could be considerably changed with time. The results show that the fluidity and filling ability for geothermal well cementation can be properly controlled with water content and additives for adverse geothermal well environment.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.10a
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• pp.69-72
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• 1999

In this study, we blended 2 grades of ultra fine cement using the results of previous stud. And the cement slurry was produced by water each water/cement ratio. The slurries were observed hydration phenomena during 28 days with SEM, XRD and DSC. The specimen made by slurry were evaluated with the hardened properties such as compressive strength, flexural strength length change and water absorption. And were tested the adhesive strength of specimen made by injecting the slurry between mortar bars.

• Advances in concrete construction
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• v.8 no.1
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• pp.47-54
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• 2019

Portland cement pervious concrete has been expected to have good water permeability, mechanical properties and abrasion resistance at the same time when Portland cement pervious concrete is applied to the actual vehicle pavement. In this study, the coarse aggregate and cement were replaced by the fine aggregate and the silica fume to improve actual road performance Portland cement pervious concrete. The Mechanical properties, the water permeability and the abrasion resistance of Portland cement pervious concrete were investigated. The results show that the compressive strength, the flexural strength and the abrasion resistance are increased when the fine aggregate and the silica fume are added to Portland cement pervious concrete separately. However, the porosity and the water permeability are decreased simultaneously. With assistance of silica fume and fine aggregate simultaneously, Portland cement pervious concrete could achieve a higher strength. The compressive strength, the flexural strength and the abrasion resistance of Portland cement pervious concrete mixed with 5% fine aggregates and 8% silica fume are increased by 93.1%, 65% and 65.2%, respectively. The porosity and the water permeability are decreased by 22.4% and 85% when Portland cement pervious concrete is mixed with 5% fine aggregate and 8% silica fume. Therefore, the replacement ratio of the fine aggregates and the silica fume should be considered comprehensively and determined on the premise of ensuring the water permeability coefficient.

• Journal of the Korea Institute of Building Construction
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• v.15 no.2
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• pp.169-175
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• 2015

Recently, a stone is preferred as a cladding materials because of its outstanding durability and luxurious character. However, because of running out of natural resources and restriction of production, it is expected that difficulty of stable supply, and thus alternative cladding materials for concrete wall is needed. Therefore, in this research, as an alternative cladding materials, exposed-aggregate concrete is studied using saccharin based retarder. For evaluating factors, changing water-to-cement ratio, dosages of saccharin-based retarder, and timing of water jet washing were tested on the surface properties of exposed-aggregate concrete. As a result, the most favorable surface performance was obtained at 0.75 day after the placing in 25% of water-to-cement ratio, and at one day after the placing in 35 and 55% of water-to-cement ratio, 1.5 day after the placing in 65% of water-to-cement ratio with $24m{\ell}/m^2$ of retarder application.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.583-586
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• 2005

Strength of concrete is very important factor in design and quality management and may represent overall quality of concrete. Such strength of concrete may differ depending on amount of cement mixed, water and fine aggregate ratio. Classic concrete products have been produced mainly with ordinary portland cement(hereinafter 'cement'), water and fine aggregate as shown above, but various additives and mixture materials have been used for concrete manufacturing, along with development of high functional concrete and diversification of structures. Various kinds of chemical mixtures agents and mixture materials have been used as it requires concretes with other features which cannot be solved with existing materials only, such as high strength, high flexibility and no-separation in the water. Such addition of various mixture agents may cause change in cement hydrate, affecting strength. Hydration of cement is the process of producing potassium hydroxide, C-S-H, C-A-H and Ettringite, while causing heat generation reaction after it is mixed with water, and generation amounts of such hydrates play lots of roles in condensation and hardening. This study aims to analyze its strength and features with hydrates by making specimen according to curing temperature, types of mixture agent, mixing ratio and ages and by analyzing such hydrates in order to analyze role of cement hydrate on early strength of concrete.