• Proceedings of the Korea Concrete Institute Conference
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• 2002.05a
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• pp.749-754
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• 2002

The safety and serviceability of concrete structures are influenced by corrosion of steel bars in concrete. Several methods have been available to protect the reinforcing bars from corrosion. Among them, the surface coating method is one of the easiest way to apply to concrete structures. However, the realistic guideline for surface coating materials has not been established yet in this country. In this study, in order to establish a reasonable technical guidelines which include the test method, quality criteria, and construction method, the performances of surface coating materials were evaluated.

• Computers and Concrete
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• v.5 no.4
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• pp.279-293
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• 2008

In the present paper a 3D thermo-hygro-mechanical model for concrete is used to study explosive spalling of concrete cover at high temperature. For a given boundary conditions the distribution of moisture, pore pressure, temperature, stresses and strains are calculated by employing a three-dimensional transient finite element analysis. The used thermo-hygro-mechanical model accounts for the interaction between hygral and thermal properties of concrete. Moreover, these properties are coupled with the mechanical properties of concrete, i.e., it is assumed that the mechanical properties (damage) have an effect on distribution of moisture (pore pressure) and temperature. Stresses in concrete are calculated by employing temperature dependent microplane model. To study explosive spalling of concrete cover, a 3D finite element analysis of a concrete slab, which was locally exposed to high temperature, is performed. It is shown that relatively high pore pressure in concrete can cause explosive spalling. The numerical results indicate that the governing parameter that controls spalling is permeability of concrete. It is also shown that possible buckling of a concrete layer in the spalling zone increases the risk for explosive spalling.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2006.05a
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• pp.5-8
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• 2006

High strength concrete has been increasingly used in high rue building and it is very obvious re consider fire resistance performance of that. Unlike the normal strength concrete, high strength concrete in sudden elevating temperature at fire is susceptible to spalling with severe explosion and surface split, due to high density of concrete. In order to endure the spalling, inner space temperature of concrete should be control less than certain point. Therefore this study investigated the influence of covering materials on high strength concrete finishing spray-on materials of fiber composite spray mortar(FCSM). Both polypropylene(PP) and polyvinyl alcohol(PVA) fiber were used in this test. Test showed that concrete, covering 18mm mortar containing PVA fiber and confining metal lath 2.3mm thickness, decreased 50% of main bar ambient temperature. compared with control concrete. In addition, concrete covering 18mm mortar without fiber caused falling of covering materials and then it was exposed in elevating temperature. As a result, spatting of the concrete occurred same as control concrete. However, concrete covering spray-on mortar containing PVA or PP fiber resisted spatting occurrence.

• Journal of the Korean Wood Science and Technology
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• v.23 no.2
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• pp.83-87
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• 1995

Impact-bouncing height of steel balls dropped from 1m height on various floor materials were measured to evaluate impact-bouncing characteristics depending on floor materials and the effect of these properties on walkability and fatigue of humanbody. Stone and tile finished concrete floor showed the highest bouncing height of around 70%, and soil showed the lowest bouncing height of around 3%. The second highest bouncing height was about 40% which corresponded to terazo finished concrete floor and about twice as high as the bouncing height on concrete floor without finishing. The impact-bouncing height could be lowered to 15~20% by using gum tile on concrete floor. Steel showed similar bouncing height to concrete floor, and wood-based materials showed the second lowest bouncing height next to soil. Among wood-based materials, hardwood species having higher specific gravities showed relatively high bouncing height of 8~24%, softwood species having low specific gravities showed relatively lower bouncing height of 5~18%, and wood composites showed bouncing height of 8~18%. Among all the materials used in this study, wood-based floor materials corresponded to the bouncing height of 10~15% which is considered to be best for humanbody. Surface painting on wood-based materials increased the bouncing height, and the number of bouncing of steel balls after dropping from 1m height increased as the bouncing height increased.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2006.05a
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• pp.39-42
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• 2006

Recently, more highly effective construction materials are needed for the reasonable and economical structure system is required as the construction structures become more multi storied, large-sized and diversified. That is to say, the highly qualified concrete, the molt universal construction material is positively promoted as a part of plan to establish the effective space according to the dead load of structures and diminish of segment profile and to build up the economic structures. In particular, it is tendency of that the study for high strength concrete increases and construction example of reinforced concrete (RC) using the high strength concrete partially increases. However, the high strength concrete has the problems such high brittleness and low ductility. Specially, for the high strength concrete, it has different strength from normal concrete as the internal temperature goes up steadily due to high heat of hydration by the quantities of highly level of cement, so the concrete which is mixed with various scible materials is used. This study conducted a basic experiment to conclude an adequate selection of materials and to calculate an optimal mixing proportion of those materials to produce High-strength concrete. And also we conducted an experiment to find out basic properties of this concrete such as slump-flow, strength.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.05a
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• pp.192-195
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• 2004

Recently, the development of construction materials is rapidly advancing. Especially, the rate of development of cement based construction materials is much quicker than steel or composite materials. In order to optimize the ductility and strength of cement based materials, Micro-mechanics based fiber concrete called Engineered Cement Composite (ECC) is developed and studied extensively by many researchers in the field. Due to ECC's remarkable flexural strain and strength capacities, many leading nation (i.e., US, Japan, and European countries) are currently using ECC in actual constructions. In this study, ECC with internationally competitive material capacities is manufactured using domestic materials. Then, unreinforced concrete beams are repaired using ECC with $10\%,\;20\%,\;30\%$ of concrete specimen height Using 4 point bending test, the flexural strength of repaired flexural members are determined. The results show that ECC manufactured with domestic materials can be effectively used for repairing materials.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.05a
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• pp.637-642
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• 2002

In this study, the experiments of recycled aggregate concrete with fly ash and special blended slag powder or diatom calcined at 650$\circ$ were performed on compressive strength, shrinkage and creep. The compressive strength of concrete with recycled aggregate and pozzolanic materials were higher than that of concrete with crushed stone and OPC. On the other hand, the shrinkage and creep of concrete with recycled aggregate and pozzolanic materials was smaller than that of concrete with crushed stone and OPC. Futhermore, the shrinkage and creep of recycled aggregate concrete with fly ash and special blended slag powder was a little decreased that of recycled aggregate concrete with fly ash and diatom. Relationship between compressive strength and creep coefficient was shown to the linear relation like as $\sigma$$_{c}$= -30CF＋404.4.

• Computers and Concrete
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• v.25 no.2
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• pp.111-118
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• 2020

The construction field must always explore sustainable ways of using its raw materials. Studying the environmental impact generated by reinforced concrete raw materials during their production and transportation can contribute to reducing this impact. This paper initially presents the carbon dioxide emissions from reinforced concrete raw materials, quantified per kilo of raw material and per cubic meter of concrete with different characteristic strengths, for southern Brazil. Subsequently, reinforced concrete elements were optimized to minimize their environmental impact and cost. It was observed that lower values of carbon dioxide emissions and cost savings are generated for less resistant concrete when the structural element is a beam, and that reductions in the cross section dimensions of the beams, sized based on the use of higher strength concrete, may not compensate for the increased environmental impact and costs. For the columns, the behavior differed, presenting lower values of carbon dioxide emissions and costs for higher concrete strengths. The proposed methodology, as well as the results obtained, can be used to support structural projects that have less impact on the environment.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.04a
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• pp.805-810
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• 2000

The purpose of this study is to predict long-term structural safety on the Yonggwang Unit 3 prestressed concrete containment building. The aging-related degradations of its main structural materials are investigated and the effects of the property variation of time-dependent materials on the structural behavior of containment building are also assessed through the analysis on the ultimate pressure capacity. The nonlinear finite element analyses for both the design criteria condition a the present aging condition are conducted to assess the present structural capacity of the containment building As a result, it is verified that the structural capacity of the Yonggwang Unit 3 containment building under the present aging condition is judged to be still rugged. n addition, the sensitivity of the ultimate pressrue capacity of containment building according to th degradation levels of the structural materials are assessed. Finally, it is showed that the sensitivity levels are in the order of the tendon, rebar and concrete in case of individual material degradations, and the tendon-rebar, tendon-concrete and rebar-concrete in case of coupled material degradations.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.04a
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• pp.888-895
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• 2000

As conventional grouting materials for the sheath such as cement slurry or cement-mortar are mixed and pumped in site, those harden with bleeding or shrinkage and meets low compressive strength. Also the materials haven't always same cements, sand size distributions, additives in site, so those materials have unstable quality properties. We have studies on ready-mixed-mortar for grouting pretensioned or post-tensioned cables and rods to encapsulate the steel so that we have developed a formulation of specially selected, flowable, shrinkage-compensating materials.