• KIEAE Journal
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• v.12 no.3
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• pp.115-122
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• 2012

Based on previous research and existing literature, this study examines the development of admixture, which increases the early concrete strength (1 and 3 day) by mixing blast furnace slag cement and concrete stimulant. The research on early strength development of concrete is necessary in dealing with the drawbacks of slow early strength concrete on site and to shorten the construction time. The study confirmed that when a high alkaline mortar mixture is mixed with blast furnace slag, the early strength of admixture exceeds that of ordinary portland cement (OPC). The use of calcium chloride ($CaCl_2$) promotes hydration of cement at low temperature and show similar strength as the blast furnace slag admixture. Although calcium chloride seems economically advantageous, it causes steel corrosion and its use in concrete should be further studied in-depth.

• Korean Journal of Metals and Materials
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• v.48 no.7
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• pp.598-604
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• 2010

Tensile tests are widely used for evaluating mechanical properties of materials including flow curves as well as Young's modulus, yield strength, tensile strength, and yield point elongation. This research aims at analyzing the plastic flow behavior of high strength steels for automotive bodies using the finite element method in conjunction with the viscoplastic model considering the yield point elongation phenomenon. The plastic flow behavior of the high strength steel was successfully predicted, by considering an operating deformation mechanism, in terms of normalization dislocation density, and strain hardening and accumulative damage of high strength steel using the modified constitutive model. In addition, the finite element method is employed to track the properties of the high strength steel pertaining to the deformation histories in a skin pass mill process.

• Advances in concrete construction
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• v.5 no.6
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• pp.659-669
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• 2017

Grouts compared to other material sources, could be highly sensitive to cold weather conditions, especially when the compressive strength is the matter of concern. Grout as one the substantial residential building material used in retaining walls, rebar fixation, sidewalks is in need of deeper investigation, especially in extreme weather condition. In this article, compressive strength development of four different commercial grouts at three temperatures and two humidity rates are evaluated. This experiment is aimed to assess the grout strength development over time and overall compressive strength when the material is cast at low temperatures. Results represent that reducing the curing temperature about 15 degrees could result in 20% reduction in ultimate strength; however, decreasing the humidity percentage by 50% could lead to 10% reduction in ultimate strength. The maturity test results represented the effect of various temperatures and humidity rates on maturity of the grouts. Additionally, the freeze-thaw cycle's effect on the grouts is conducted to investigate the durability factor. The results show that the lower temperatures could be significantly influential on the behavior of grouts compared to lower humidity rates. It is indicated that the maturity test could not be valid and precise in harsh temperature conditions.

• Journal of the Korea Concrete Institute
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• v.25 no.1
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• pp.3-9
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• 2013

In ultra high strength concrete, when electric arc furnace oxidizing slag is substituted for sea sand as fine aggregate, compressive strength was improved about 15 MPa. To figure out the cause of the improvement in compressive strength, this study considered the dissolution characteristics of Ca component in fine aggregate and examined the microstructure, porosity, microhardness, and Ca/Si mole ratio on the interface of fine aggregate and paste. And to examine the mechanism of strength improvement resulted from the shape of fine aggregate, this study measured the surface roughness of fine aggregate with AFM. According to the result of this experiment, the mechanisms of strength improvement in ultra high strength concrete resulted from the use of electric arc furnace oxidizing slag as fine aggregate can be divided into chemical and physical mechanisms. In the chemical mechanism, the soluble Ca component contained in electric arc furnace oxidizing slag is dissolved and forms a hydrate between fine aggregate and paste to improve the interlocking strength of fine aggregate-paste. Also, it makes the microstructure around the fine aggregate. And in the physical mechanism, electric arc furnace oxidizing slag has a twice greater surface roughness than sea sand, so the interlocking strength between fine aggregate and paste increases, which contributes to the development of compressive strength.

• Proceedings of the Korea Concrete Institute Conference
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• 1997.04a
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• pp.323-328
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• 1997

The strength of concrete depends on factors of materials, composition and manufacturing method. Among these factors, preparatory experiments are to consider and analyze the factors on compressive strength of ultra-high strength concrete according to types of aggregate, binder content, water-binder ratio, and curing methods. And the final experiment to develop the ultra-high strength over 3,000kgf/$\textrm{cm}^2$ is based on these preparatory experiments. As the result of this final expriment. We could manufacture the ultra-high strength concrete with a marvelous compressive strength concrete with a marvelous compressive strength of 3,116kgf/$\textrm{cm}^2$. This study is to compare and analyze the manufacturing system of ultra-high strength concrete of 3,116kgf/$\textrm{cm}^2$ compressive strength in the side of material development of construction industry.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.147-152
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• 2001

The purpose of this study is to ascertain the strength properties of water-permeable polymer concretes with SBR latex and redispersible polymer powder. The water-permeable polymer concretes using SBR latex and redispersible polymer powder with water-binder ratio of 29%, polymer-cement ratios of 0, 5, 10, 15 and 20% are prepared, and tested for compressive strength, tensile strength, flexural strength, water permeability. From the test results, improvements in the strength properties of the water-permeable polymer concretes due to the addition of the SBR latex and redispersible polymer powder are discussed.

• Proceedings of the Korea Concrete Institute Conference
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• 1993.10a
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• pp.11-17
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• 1993

In this study, the fundamental properties of High-Strength Concrete(HSC), such as the slump loss, the temperature increment, the strength development, are considered by experiment. In reducing the temperature and the slump loss, and developing the strength of HSC, the application of silica fume as an admixtures is very effective. And when gypsum is added, the slump loss is reduced and the strength of HSC is improved remarkably, but the temperature of concrete is increased, thus a more study to reduce the temperature increment is required

• Proceedings of the KSR Conference
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• 2001.05a
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• pp.193-199
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• 2001

In this study, the carbody design of the rubber tired AGT(Automated Guide-way Transit System) under development by KRRI was numerically analysed to evaluate its structural strength according to the standard specifications for Korean LRT (Light Rail Transit). The numerical results showed that the detail design of the carbody was strong enough to satisfy the specifications with respect to the axial compression strength, the vertical strength and the vertical stiffness(natural frequency). However, the carbody design had some problems on the fatigue strength by twist loadings. So, it was recommended that the carbody design should be modified to improve the twisting strength by reinforcing the front end structures.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2020.06a
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• pp.187-188
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• 2020

Recently, some researchers have found, as a part of the development of new materials, the rice straw ash can also be used as a pozzolanic material for concrete considering similar chemical properties of rice straw ash to that of rice husk ash. Therefore, the purpose of this study was to improve compressive strength of concrete adding agriculture by-product. Compressive strength were tested on rice straw ashes at 600℃ to identify improving strength effect.

• Smart Structures and Systems
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• v.26 no.2
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• pp.147-156
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• 2020

This numerical study demonstrates the porosity conditions and the intensity of the interactions with the aggressive agents. It is established that the density as well as the elastic modulus are correlated to ultrasonic velocity The following investigation assessed the effects of cement grade and porosity on tensile strength, flexural and compressive of Ultra High Performance Concrete (UHPC) as a numerical model in PLAXIS 2d Software. Initially, the existing strength-porosity equations were investigated. Furthermore, comparisons of the proposed equations with the existing models suggested the high accuracy of the proposed equations in predicting, cement grade concrete strength. The outcome obtained showed a ductile failure when un-corroded reinforced concrete demonstrates several bending-induced cracks transfer to the steel reinforcement. Moreover, the outcome also showed a brittle failure when wider but fewer transverse cracks occurred under bending loads. Sustained loading as well as initial pre-cracked condition during the corrosion development have shown to have significant impact on the corrosion behavior of concrete properties. Moreover, greater porosity was generally associated with lower compressive, flexural, and tensile strength. Higher cement grade, on the other hand, resulted in lower reduction in concrete strength. This finding highlighted the critical role of cement strength grade in determining the mechanical properties of concrete.