• Proceedings of the Korea Concrete Institute Conference
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• 1999.04a
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• pp.117-122
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• 1999

The antiwashout concrete which is a type of specific concrete is manufactured by using a plenty of superplasticizer with the non-dispersible underwater concrete admixture, and the application of it on construction site is being increased. But when we measure choride ion content by using the potentiographic tester, because it is over total chloride ion content(0.3kg/㎥ under) of Korean Concrete Specification, the claim of construction site is being presented on the quality of antiwashout concrete. Accordingly, hte aim of this study is to verify actual chloride ion content of antiwashout concrete by chloride ion analysis due to chemical admixtures by performance of antiwashout concrete. In conclusion the actual chloride ion content of antiwashout concrete is overestimated by anion($OH^-, SO4^{-2}, S^{-2}, etc) of chemical admixtures, and is proved to be as low as that of ordinary concrete.

• Proceedings of the Korea Concrete Institute Conference
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• 1995.10a
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• pp.25-29
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• 1995

To perform high-strength of concrete, fine powers of pozzolan such as fly ash, silica fume mixed with cement. But mobility of cement and concrete decreased due to using of these powers. To control decrease of this mobility, it is required that mobility is improved by using of chemical admixture such as superplasticizer. We used admixtures -NSF, NM-2, NT-2 etc- in order to improve mobility of cement paste being substituted by 10, 20% of pozzolans respectively. It proved that optimum dosage of NSF, NT-2 was 2.0% for being substituted 10%, 3.0% for 20% so as to increase mobility of cement paste mixed paste mixed with fine powers of pozzolan at W/C=0.40.

• KCI Concrete Journal
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• v.11 no.3
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• pp.175-180
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• 1999

In order to predict the onset of the corrosion of steel bars in concrete, a mathematical model was presented to observe the diffusion of chloride ion in aqueous phase, the adsorption and desorption of chloride ions to and from the surface of solid phase of concrete, and the chemical reaction or chloride ions with solid phase. The finite element method was employed to carry out the numerical analysis. The chlorides enetrating through the wall of the concrete structure from the external environment and the chlorides contained in the concrete admixture were confirmed to be two important factors to determine the onset of the corrosion of steel bars.

• Bulletin of the Korean Chemical Society
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• v.3 no.4
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• pp.133-139
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• 1982

It has been presumed that the molten sulfur above $159^{\circ}C$ consists of an equilibrium mixture of $S_8$ rings and $S_x$ polymers where the number average degree of polymerization, P, is large. But it is known that admixture of halogens with liquid sulfur greatly reduce the viscosity. Constructing a new equilibrium equation, it is possible to evaluate the viscosity when halogens are added to liquid sulfur. Calculated viscosity is in good agreement with experimental values. Using the proposed model, the thermodynamic properties of liquid sulfur are also calculated over a wide range of temperature which the sulfur exists as the polymer.

• Journal of the Korea Institute of Building Construction
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• v.9 no.2
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• pp.85-91
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• 2009

W/C and unit volume, which significantly affect quality of concrete related to strength and durability, are regulated at below $185kg/m^3$ for regular concrete generally used in standard specification for constructions. The aim of this research is to develop chemical admixture and find out its potential use by identifying characteristics of admixtures added to soft concrete and hardening concrete, of which content ratio of component for each type of admixtures is subject to change in accordance with unit volume within KS' allowable range. Sodium gluconate, polyoxyethylene nonylphenyl ether, poly carboxylic copolymer in slump, which is characteristic of soft concrete, are deemed highly sensitive while there is no air entrainment except for $10\sim70%$ in WE, WR component content ratio and NP. In hardening concrete, strength in general showed higher action in compressive strength and tensile strength than in plain strength. Use of proper AE agent and AE water reducing agent at the same time is deemed to be used as chemical admixtures capable of manufacturing high-quality, high-quantity concrete.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2009.11a
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• pp.73-76
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• 2009

In ultra-high-strength concrete, chemical shrinkage is larger than drying shrinkage due to using a large amount of cement and admixtures, and this is a factor deteriorating the quality of structures. Thus, we need a new technology for minimizing the shrinkage strain of ultra-high-strength concrete. So, this study have prepared super-high-strength concrete with specified mixing design strength of over 100MPa and have evaluated a method of reducing chemical shrinkage by using expander and shrinkage-reducing agent. According to the results of this study, with regard to the change in length by chemical shrinkage, an expansion effect was observed until the age of seven days. The expansion effect was higher than previous research that used only expander or shrinkage reducing agent. In addition, ultra-high-strength concrete showed a shrinkage rate that slowed down with time, and the effect of the addition of expander material on compressive strength was insignificant. That is shown that required more database to be accumulated through experimental research for the shrinkage strain of members.

• Journal of the Korea Concrete Institute
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• v.27 no.6
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• pp.695-703
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• 2015

Acceptance criteria for chemical admixtures of cement concrete were investigated in domestic and international specifications. The reliability was verified for solid content test method of chemical admixture examined statistical analysis by round robin test. The applicability of FT-IR spectroscopy for qualitative measurement of multi-compound chemical admixtures verified. From solid content experimental results, outlier analysed using Cochran, Grubbs and Dickson's Q test. Repeatability and reproducibility standard deviation for solid content results showed 0.25 and 0.098% respectively according to KS A ISO 5725-2 procedure, it can be confirmed reliability of test methods. FT-IR spectrum of liquefied or oven-dried chemical admixtures condition showed big differences. It is needed that the FT-IR analysis is performed on dry material. However there's no difference with the applicability of FT-IR spectroscopy for multi-compound chemical admixtures. So the utility of method analysis could not identify.

• Journal of the Korea Concrete Institute
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• v.24 no.4
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• pp.435-444
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• 2012

High performance concrete mixes are selected and corresponding test specimens are made for the study of chloride diffusion coefficient at reference time. The concrete mixes were same designs as those used in construction of bridges located in a marine environment. Mix design variables included binder type, water-to-binder ratio, mineral admixtures to total binder weight substitution ratio, fine aggregate source, chemical water reducer admixture type for high strength and high flowability, and target slump or slump flow. The test results showed that the diffusion coefficients at reference time varied significantly according to the type of mineral admixtures and their substitution ratios. A model for diffusion coefficient at reference time considering the type of mineral admixture and the substitution ratio was developed. Diffusion coefficients from the developed model were compared with those from literature review, a previous model, and additional test results. All of the comparisons verified that the developed model can reasonably predict diffusion coefficients and the application of the model to the durability design against chloride penetration is appropriate.

• Journal of the Korean Society of Marine Environment & Safety
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• v.14 no.4
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• pp.289-295
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• 2008

The disposal of constructive waste is emerging as a national and social issue and the recycled powder generated by the production of reproductive aggregate is all being abolished or buried Analysis on the harmful effect of recycled powder indicated that because it contained massive cytotoxicity, it could derive secondary pollution to soil and subterranean water. This study set on an idea that one way to recycle recycled powder was to use it as a compound of concrete. In order to study that prospect, recycled powder, instead of cement, was mixed and a comparative analysis was conducted on the mechanical properties and workability. From experimental results, it was judged that application of recycled powder of cement replacement ratio below 20% was available with chemical admixtures. Also application of recycled powder was available to high strength concrete.

• Computers and Concrete
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• v.17 no.6
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• pp.801-814
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• 2016

An alternative type of building system with masonry units is extensively used nowadays to reduce the emission of CO2 and embodied energy. Long-term performance of such structures has become essential for sustaining the building technology. This study aims to assess the strength and durability properties of concrete prepared with unprocessed bagasse ash (BA) and silica fume (SF). A mix proportion of 1:3:3 was used to cast concrete cubes of size $100mm{\times}100mm{\times}100mm$ with various replacement levels of cement and tested. The cubes were cast with zero slump normally adopted in the manufacturing of hollow blocks. The cubes were exposed to acid attack, alkaline attack and sulphate attack to evaluate their durability. The mass loss and damages to concrete for all cases of exposures were determined at 30, 60, and 90 days, respectively. Then, the residual compressive strength for all cases was determined at the end of 90 days of durability test. The results showed that there was slight difference in mass loss before and after exposure to chemical attack in all the cases. Though the appearance was slightly different than the normal concrete the residual weight was not affected. The compressive strength of 10% bagasse ash (BA) as a replacement for cement, with 10% SF as admixture resulted in better strength than the normal concrete. Hence concrete with 10% replacement with BA along with 10% SF as admixture was considered to be durable. Besides solid concrete cubes, hollow blocks using the same concrete were casted and tested simultaneously to explore the possibility of production of masonry units.