• Computers and Concrete
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• v.26 no.3
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• pp.257-273
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• 2020

Concrete bond strength with steel re-bars depends on multiple factors including concrete-steel interface and mechanical properties of concrete. However, the hydration development of cementitious paste, and in turn the mechanical properties of concrete, are negatively affected by cold weather. This study aimed at exploring the concrete-steel bonding behavior in concrete cast and cured under freezing temperatures. Three concrete mixtures were cast and cured at -10 and -20℃. The mixtures were protected using conventional insulation blankets and a hybrid system consisting of insulation blankets and phase change materials. The mixtures comprised General Use cement, fly ash (20%), nano-silica (6%) and calcium nitrate-nitrite as a cold weather admixture system. The mixtures were tested in terms of internal temperature, compressive, tensile strengths, and modulus of elasticity. In addition, the bond strength between concrete and steel re-bars were evaluated by a pull-out test, while the quality of the interface between concrete and steel was assessed by thermal and microscopy studies. In addition, the internal heat evolution and force-slip relationship were modeled based on energy conservation and stress-strain relationships, respectively using three-dimensional (3D) finite-element software. The results showed the reliability of the proposed models to accurately predict concrete heat evolution as well as bond strength relative to experimental data. The hybrid protection system and nano-modified concrete mixtures produced good quality concrete-steel interface with adequate bond strength, without need for heating operations before casting and during curing under freezing temperatures down to -20℃.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2009.11a
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• pp.93-96
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• 2009

The objective of this study is to analyze the insulation characteristics of the polylon hybrid fiber inserted high-strength RC beam and slab produced as a single body and the results of this study can be summarized as follows. In the spalling mechanism as an insulation characteristic, the slab of the single body type specimen shows an exposure in concrete covers at the center of slab and that leads to the spalling, which exposures reinforcing bars. In the case of the beam, the spalling was presented at several sections as a type of peel spalling before and after 10 minutes from the insulation test. Whereas, although the internal temperature history of concrete represents the highest range as 581℃ in the case of the center of the bottom of beam base, it can be considered that it satisfies the regulation of insulation certification.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.35 no.11
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• pp.137-146
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• 2019

Recently, the Near-Surface-Mounting method using Fiber reinforced polymer (FRP) has been developed and applied to the reinforcement of many concrete structural members. However, as a part of the fire resistance design, there is a lack of research related to fire insulation for the areas reinforced with FRP. In case of NSM reinforcement, there is a difference in the transferred temperature from the external surface to the groove corresponding to the location of the groove where the FRP is embedded, and the effect of this should be reflected in the fireproof insulation design. Therefore, in this study, after forming grooves for surface embedding in concrete blocks, fireproof insulation reinforcement was performed using Calcium Silicate (CS) fireproof board and an experiment to evaluate the temperature transfer was performed. By observing the temperature at these groove positions, the reduction of temperature transfer according to fireproof insulation detail was studied. As a result, when the NSM-FRP is properly fire-insulated using the CS-based fireproof board, the epoxy inside the groove does not reach its glass transition temperature until the external temperature reaches $800^{\circ}C$.

• Magazine of the Korea Concrete Institute
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• v.25 no.6
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• pp.26-30
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• 2013

• Magazine of the Korea Concrete Institute
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• v.25 no.6
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• pp.31-34
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• 2013

• Proceedings of the Korean Institute of Building Construction Conference
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• 2014.11a
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• pp.188-189
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• 2014

Nowadays, many research execute about sandwich-insulation wall for durability of wall and retaining insulation performance. But sandwich-insulation, different exterior and interior insulation, need to form-tie which supporting both side form. And because of it penetrate concrete wall, it is worried about thermal-bridge phenomenon to form-tie. So, this research classify penetration type and buried type and analysis thermal-phenomenon of each type's form-tie and insulation performance. As a result, all form-tie type little occur thermal-bridge but penetration form-tie have superior insulation performance and low U-value.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2013.11a
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• pp.132-133
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• 2013

External Insulation Method is to place the insulation on the outside of concrete. External Insulation Method is better than Internal Insulation Method to the protection of structure. However, The phenomenon that External Insulation falling from the structure occurs frequently. Apply method of External Insulation is divided Wet Construction, Dry Construction and Wet & Dry Construction. The purpose of this study is to test Bonding Strength of External Insuation. Furthermore, on the basis of this study, External Insulation Method determines the effective development will be made.

• Journal of the Korea Concrete Institute
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• v.25 no.3
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• pp.331-338
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• 2013

Under the paradigm of sustainable green growth at the national level, various researches and applications for energy saving in the construction field has been attempted. As a part of energy saving efforts, lightweight concrete was investigated for thermal insulation concrete with phase change material (PCM) which has high heat storage capacity. As a part of energy saving efforts, thermal insulation concrete was investigated and evaluated with lightweight aggregate impregnated by PCM which has high heat storage capacity. As a result, it is found that concrete with lightweight aggregate impregnated by PCM is effective to prevent its quality deterioration by reducing water absorption rate of lightweight aggregate. In addition, it has shown that concretes using lightweight aggregate and impregnated lightweight aggregate improve heat insulation property 33% and 40~43% compared with using normal aggregate, respectively. It is that the lightweight aggregate concrete with impregnated lightweight aggregate has 12~14% lower thermal conductivity than unimpregnated.

• Journal of the Korea Safety Management & Science
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• v.12 no.3
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• pp.121-128
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• 2010

This is to show some basic data for introducing both circulated aggregate and recycled powder producing waste concrete. Standard-mixing design for 24MPa has been basically used and added and replaced normal aggregate with recycled powder made of waste concrete. In addition, polycarboxylate high-range water reducing agent has been used because recycled powder is missing adhesive strength and it is not compare with cement's adhesive strength. Compressive strength with powder mixture of 2%, 4%, 6%, 8%, and 10% has been decreased down to 80% of normal concrete material strength without recycled powder mixture. $200^{\circ}C$, $400^{\circ}C$ and $600^{\circ}C$ heated concrete were compressively tested in order to find out concrete strength resistant to high temperature. heat capacity was also tested, based on the expectancy of its low conductivity. In addition, thermal conduction test was tested in order to find out concrete insulation. According to this test, when concrete was tested by fire resistance, it using the circulation aggregate was same resulted by concrete using the natural aggregate. also, recycle powder was not effecting insulation performance. but it is fit to standard on concrete insulation of building law.

• Journal of the Korea Concrete Institute
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• v.15 no.3
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• pp.392-399
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• 2003

This paper discusses the validities of insulating curing of cold weather concreting at early stage by applying insulation forms. Tests were carried out using modified insulating form combining existing insulating form and various other insulations in order to develop improved insulation form. Temperature history of concrete using various insulating forms and insulation was measured to determine most effective combination of insulting form. According to results, as for the wall form, under the curing temperature of $-10^{\circ}C$, the temperature of concrete using Euro form drops sharply before 24 hours and lasts below $0^{\circ}C$ for 7 hours. The temperature of concrete using the form combining Polypropylene panel, styrofoam and plywood panel keep above $0^{\circ}C$. And, it is confirmed that the form mentioned above has a favorable effects on enhancing strength development of concrete and the cost to make the forms shows more reasonable than that of existing forms. However, as for the combination methods of insulation form for slab, which is composed of insulating form at the bottom of slab and various surface curing materials at the top of slab, in case of exposed condition at the top of slab, temperature history of concrete goes below $0^{\circ}C$ after 10 hours. In case of the combination of vinyl sheet and curing blanket, it drops below $0^{\circ}C$ after 42 hours. However, in case of the combination of vinyl, styrofoam and curing blanket, it does not go below $0^{\circ}C$ until 55 hours. Accordingly, compared to the case of exposure and the combination of vinyl and curing blanket, it indicates that the combination mentioned above has more effective insulating performance.