• Journal of the Korean Society of Industry Convergence
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• v.10 no.4
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• pp.207-211
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• 2007

The durable lifetime of RC structures is shortened by various reasons, which are the generation of cracks in construction and service term, the exterior deterioration according to climatic condition, the surface damage due to chloride attack and the corrosion of reinforced bars. The durability of concrete structures is nevertheless able to be increased by the method and the material of reinforcement and repair. The epoxy resin is widely used for reinforment and repair of concrete because of the superiority in mechanical property, adhesive property, abrasion resistance, impact resistance and chemical resistance. The epoxy cement mortar with hardening agent has a lot of disadvantages that are troublesome mixing work, weakened weatherability and high cost for hardening agent. In this study, the mix proportion of mortar is presented just only with epoxy resin and some admixtures, and the test result of mortar without hardening agent shows the higher strength than the mortar with hardening agent. In the mix proportion, the weight of epoxy resin must be less than 15% of the unit weight of cement, and 10% of unit weight of cement is adequate for the weight of admixtures.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.19 no.4
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• pp.320-328
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• 2007

The durability of marine concrete structures is severely degraded by corrosion due to seawater attack and diffusion of chloride in concrete. The deduction of durability causes high repair cost for maintenance of marine concrete structure. So, the applicability of high-durable materials is investigated to improve the durability in marine concrete structures. For these, the characteristics of corrosion prevention of marine concrete structures mixed with the mineral admixtures(SF, FA and BFS), the modified steel(stainless and coating steel), and corrosion inhibitors are evaluated using electro-chemical methods. As a results of this study, it is quantified for the effect of promotion of durability by high-durability materials in marine concrete structures.

• Journal of the Korean Ceramic Society
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• v.47 no.5
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• pp.387-393
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• 2010

To improve concrete quality one of the most widely used chemical admixtures is polycarboxylate type superplasticizer. Unlike lignosulfonate and naphthalene-sulfonate, it has high dispersion property and excellent sustainable dispersion property for cement and concrete. Thus, polycarboxylate type superplasticizer has been widely used as a high-performance water reducing admixture together with silica fume in high-performance concrete and other applications for the dispersion of high-strength concrete over 100 MPa. However, even though there have been many studied on the dispersion of concrete by the structure of polycarboxylate type superplasticizer, there have a few studied that clarified the relationships between its rheological properties and microstructure properties in the early hydration behavior of ordinary portland cement. To investigate the correlations between the rheological properties and microstructure of cementitious materials with polycarboxylate type superplasticizer, this study experimented on the rheology, pore structure, heat evolution, and consistency in early hydration as well as on the compressive strength by early dispersion characteristics.

• 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.

• Journal of the Korean Recycled Construction Resources Institute
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• v.7 no.4
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• pp.310-315
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• 2019

This study conducted a series of studies to find alternative ways to use Chlorine Bypass System-dust(CBS-dust) in cement production. The results of engineering characteristics of CBS-dust are summarized as follows. First of all, the density of CBS-dust is 2.40, lighter than cement and the pH was 12.50 which was strong alkaline. In terms of particle size, it was 11.70 ㎛ which was finer than cement. With chemical properties, calcium oxide(CaO) was the highest as 35.10%, potassium oxide(K₂O) was 32.43%, potassium chloride(KCl) was 19.46%, sulfur oxide(SO₃) was 6.81%, and the remaining chemical components are SiO₂, Fe₂O₃, Al₂O₃, MgO, and the like. Therefore, if CBS-dust is used as early-strength chemical admixtures in the concrete secondary products that use a large amount of mineral admixtures without rebar, it can be an effective method for increasing the strength of concrete as an alkali activator and preventing early-frost damage of Cold Weather 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.

• Advances in concrete construction
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• v.5 no.6
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• pp.671-683
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• 2017

Commonly used concrete in general, consists of cement, fine aggregate, coarse aggregate and water. Natural river sand is the most commonly used material as fine aggregate in concrete. One of the important requirements of concrete is that it should be durable under certain conditions of exposure. The durability of concrete is defined as its ability to resist weathering action, chemical attack or any other process of deterioration. Durable concrete will retain its original form, quality and serviceability when exposed to its environment. Deterioration can occur in various forms such as alkali aggregate expansion, freeze-thaw expansion, salt scaling by de-icing salts, shrinkage, attack on the reinforcement due to carbonation, sulphate attack on exposure to ground water, sea water attack and corrosion caused by salts. Addition of admixtures may control these effects. In this paper, an attempt has been made to replace part of fine aggregate by tailing material and part of cement by fly ash to improve the durability of concrete. The various durability tests performed were chemical attack tests such as sulphate attack, chloride attack and acid attack test and water absorption test. The concrete blend with 35% Tailing Material (TM) in place of river sand and 20% Fly Ash (FA) in place of OPC, has exhibited higher durability characteristics.

• Journal of the Korea Concrete Institute
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• v.17 no.5 s.89
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• pp.811-818
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• 2005

It is well known that the fluidity and the fluidity loss of fresh concrete are affected by the kind of organic admixtures. Organic admixture can improve the properties of concrete. Sulfonated Naphthalene-Formaldehyde(SNF) Superplasticizer is used representatively, but has a problem in fluidity loss. In this study, we synthesized the Sulfonated Melamine-Formaldehyde(SMF) superplasticizer at the various synthetic conditions and compared the physical properties with SMF superplasticizer. SW superplasticizer is synthesized with four synthetic steps. Step 1 is hydroxymethylation, Step. 2 is Sulfonation, Step. 3 is Polymerization and Step. 4 is Stabilization. Synthesis of SMF superplasticizer depends on pH, temperature and reaction time. In this reaction, we changed the mole ratio of melamine to formaldehyde at 1:3, 1:4, and the amount of acid catalyst at Step. 3. After application of SMF superplasticizer and its mixture with SNF superplasticizer to cement pastes and mortars, we measured the physical properties of them at the different dosages(0.5, 1.0, 1.5 wt%) to cement. All samples including superplasticizer showed higher compressive strengths and slump, smaller pore size and porosity than CEM

• Proceedings of the Korea Concrete Institute Conference
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• 2002.10a
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• pp.437-442
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• 2002

Drying shrinkage is the decrease in the volume of a concrete element when it loses moisture by evaporating. Because of low water/binder ratio(W/B) and the use of chemical and mineral admixtures for high-strength concrete, the evolutions of moisture and the rate of cement hydration in high- strength concrete are significantly different from those in normal strength concrete. In this study, the drying shrinkage of high-strength concrete with and without fly ash was measured up to the age of 200 days. From the experimental test results, it was observed that the drying shrinkage decreased as the W/B decreased. As the W/B is lowered from 0.50 to 0.27, the difference of drying shrinkage between the fly ash concrete and the ordinary concrete is gradually increased.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2015.11a
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• pp.103-104
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• 2015

This study is an experiment about what affects the compressive strength by using a reducing agent (PNS based admixtures) to play cement using the cement paste based Waste Concrete Powder of waste concrete, which accounts for more than 60% of construction waste around the latest domestic and international It was. Securing the replacement of cement with Waste Concrete Powder and, by varying the admixture was to compensate for the low absorption of liquidity and obtain a fine powder. And the experiment was conducted with a constant water cement ratio and aggregate usage for the purpose of lowering the water cement ratio promoting strength development. When substituted with the experimental results of 0.3% based on 3 ~ 28 days as strength 36Mpa exhibited the highest strength.