• Proceedings of the Korea Concrete Institute Conference
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• 2005.05b
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• pp.405-408
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• 2005

The repair and reinforcement materials of the concrete structure in underwater is use to epoxy mortar for underwater-harding. Because it ensures the separation of material and a fluidity in construction, it is important to epoxy mortar This study dealt with the influence of the using of rapidly-chilled steel slag on flow, nozzle passing time, viscosity, and strength of mortar by experimental design. As results of study, this paper proved that the more the using rate of rapidly chilled steel slag increased, the more this affected the enhancement of flow, the decrease of O-lot, and the development of compressive strength, flexural strength. Also, considering the fluidity, nozzle passing time and strength of mortar, it is desirable to use RCSS300 of rapidly chilled slag.

• Journal of the Korea Concrete Institute
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• v.17 no.3 s.87
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• pp.455-464
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• 2005

Today the application of antiwashout underwater concrete to the construction sites is increasing steadily, while its reliability is in issue. Particularly, antiwashout underwater concrete is known to have very weak durability on frost attack, and hence Japan society of civil engineers(JSCE) regulated that not to use of antiwashout underwater concrete where the freezing and thawing is suspected. This study aims the improvement of the freezing and thawing resistance for antiwashout underwater concrete. From the results of fundamental test, FA20 and SG50 showed good performance in fluidity and long term compressive strength than control concrete. Meanwhile, MK10 marked the highest compressive strength through the whole curing age but a defect on fluidity was discovered. The results from the repeated freezing and thawing test show that the large volumes of air entrapped by cellulose based antiwashout underwater admixture gave bad effects to frost durability and hence not much benefits were confirmed from the use of mineral admixtures. However there were some increasing effects on frost durability of MK10 and SG50 by securing $6{\pm}0.5\%$ of entraining air. In the meantime, there was a increasing tendency of frost durability by increasing blame's fineness of ground granulated blast furnace slag.

• 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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• 2005.05b
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• pp.277-280
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• 2005

Epoxy-mortar composites have been wildly used as finishing and repairing materials in the construction because of their excellent properties. Conventional epoxy-mortars and concretes have an inferior applicability and cost performance ratio due to the two component mixing of the epoxy resin and hardener. In this study, we examined the engineering effect of compressive strength and flexible strength according to the various epoxy-hardener in underwater and humidity environment, and evaluated the hardener types and physical effect of Epoxy mortar using cement binder in underwater and air condition. In this study, it was clarified that the engineering properties of repairing epoxy-motars were effected by the type of hardener.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2022.11a
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• pp.27-28
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• 2022

In this study, the mechanical properties of resource-recycling concrete containing concrete sludge waste as main materials was compared depending on whether supercritical CO2 curing was applied for the realization of CCU technology. After supercritical CO2 curing, the compressive strength of the steam-cured specimen was lowered, but it was confirmed that the compressive strength of the underwater-cured specimen was improved.

• Journal of the Korea Concrete Institute
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• v.13 no.4
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• pp.336-345
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• 2001

The construction of underwater structures has been increased, but underwater concrete hassome problems of quality deterioration and contamination around in-situ of civil and architecture; therefore, new materials and methods for them are demanded. In this paper in-situ application of underwater antiwashout concrete which is manufactured for trio purpose of not only decreasing suspended solids and the heat of hydration but also increasing long term strength was studied. In the case of mock-up test(Ⅰ), when underwater antiwashout concrete, whose slump flow was 58 cm, was placed in the mock-up test at a speed of 24 ㎥/hr, it took about a minute to flow to the side wall, and the surface was maintained at horizontal level. In this case, compressive strength of the core specimens in each section was higher than the standard design compressive strength of 240 kgf/㎠. In the case of mock-up test(II), pH value and suspended solids of high strength underwater antiwashout concrete were 10.0∼11.0 and 51 mg/ℓ at 30 minutes later, initial and final setting time were about 30, 37 hr, and the slump flow of that was 53$\pm$2 cm. In the placement at a speed of 27 ㎥/hr, there was no large difference in flowing velocity, with or without reinforcement and flowing slope was maintained at horizontal level. In this case, compressive strength and elastic modulus of the core specimens somewhat decreased as flowing distance was far : however, those of central area showed the highest value.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2018.05a
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• pp.54-55
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• 2018

Reinforced concrete is a building material that is generally used in modern society. Securing the performance of reinforced concrete is directly connected to the durability and longevity of the building. One of the major factors that deteriorate the durability of concrete is harmful ion. Recently, the quality and improvement method of reinforced concrete for penetration of harmful ion has been studied. In this study, the bead type ion exchange resin is substituted for 0%, 3%, and 6% of the fine aggregate volume in the mortar. The speciments underwent underwater curing and were checked for compressive strengths of 3 days and 28 days. From the results of compressive strength, it can be seen that the higher the substitution ratio of the ion exchange resin, the lower the early strength and long-term strength development, especially the early strength development.

• Journal of the Korea Institute of Building Construction
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• v.4 no.2
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• pp.113-118
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• 2004

This study is a basic experiment on quality management of the compression strength of high strength concrete, aiming. at quality management of high strength mass concrete by giving the temperature hysteresis of the mass test pieces to managerial test pieces. Different from ordinary concrete, high strength concrete generally shows the temperature high rising caused by hydration heat inside the concrete. It is known that, in mass concrete, thermal stress occurs due to the difference in temperature between the inside and the outside, which causes a significant difference in compression strength between structure beams and managerial test pieces. It is also reported that there is a large difference between the compression strength of cylindrical managerial test pieces of standard underwater curing and the strength of structure beam concrete. Thus, this study made concrete test pieces in an optimal mix ratio for each strength level, and also created thermal insulation curing box and managerial test pieces. Then it carried out comparative analysis in relation to core strength and suggested equipment and a technique that can control the strength of high strength concrete mass more conveniently and accurately.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.09a
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• pp.564-569
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• 2009

Due to the uneasy controllable qualities of the substructures such as pile and foundation, which are laid on underground, geotechnical engineers have applied conservative criteria to them. Therefore, the specification criterion of cast-in-situ concrete pile, which allows only one fourth of the compressive strength of structural capacity, has forced geotechnical designers to consider the most uneconomical design regardless of satisfying the grade of quality-control, required performance, construction cost and so on. Thus, in this study, we proposed the less conservative criteria on the strength of concrete pile, based on the experimental testing results of cast-in-situ concrete piles.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.2
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• pp.1102-1108
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• 2014

This study was to compare the protection abilities of an SPF through ground or underwater casting. A mat of 1/10 scale was made and then mortar was placed on the ground and submerged conditions. A limit velocity of each mat was estimated with this experiment. As a result of the test, the mat failed because of the decrease of bearing power in the center of the waterway. On the one hand, the edge of the mat, where the velocity is slow, secures stability. The result of the limit velocity analysis suggests that a velocity of ground placement with 6.51m/s and underwater casting with 9.80m/s is the minimum to ensure stability. When SPF mat with a thickness of 0.50m is replaced with a concrete block, it is calculated to need a maximum thickness of 2.21m.