• Proceedings of the Korea Concrete Institute Conference
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• 2004.05a
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• pp.204-207
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• 2004

In this paper, mechanical properties of the high strength lightweight self-compacting concrete with simple mixed design method was investigated. Experimental tests were performed as such compressive strength, splitting tensile strength, modulus of elasticity and density of high strength lightweight self-compacting concrete. The 28 days compressive strength of high strength lightweight self-compacting concrete with the LC replacement ratio of $100\%$ reduces about $31\%$ but LF replacement ratio of $100\%$ increase about $20\%$ compared that of the control concrete. The structural efficiency of high strength lightweight self-compacting concrete increase with proportional to the replacement into of LF. The relationship between the splitting tensile strength and 28 days compressive strength can be represented by the equation $f_s=0.076f_{ck}+0.5582$. The modulus of elasticity was found to be lower than that of normal weight concrete, ranging form 24 to 33 GPa.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.05a
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• pp.43-48
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• 2001

The use of fly ash in cement and concrete industries has many benefits including engineering, economic, and ecological aspects. However, it has a disadvantage of low strength development, especially at early ages. In this study, in order to overcome this problem, the early strength accelerating agent($NA_{2}$ $SO_{4}$) was selected and applied to the production of high strength concrete(HSC) containing fly ash. It was found that the compressive strength of fly ash concrete incorporating TEX>$NA_{2}$ $SO_{4}$ has greater than that of concrete containing fly ash only until 7 days after casting. From the microstructural point of view, ettringite increased and pores decreased in fly ash concrete incorporating TEX>$NA_{2}$ $SO_{4}$ , leading to the development of early age strength. It was also found that the velocity vs. strength relationship of HSC is considerably different from that of low-strength concrete(LSC). Therefore, in order to predict early age strength of HSC, a estimation equation different from that for LSC is needed.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.5-8
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• 2005

The purpose of this study is to investigate the mechanical characteristics of plain and steel fiber high strength concrete under uniaxial and biaxial loading condition. A number of plain and steel fiber high strength concrete cubes having 28 days compressive strength of 82.7Mpa (12,000psi) were made and tested. Four principal compression stress ratios, and four fiber concentrations were selected as major test variables. From test results, it is shown that confinement stress in minor stress direction has pronounced effect on the strength and deformational behavior. Both of the stiffness and ultimate strength of the plain and fiber high strength concrete increased. The maximum increase of ultimate strength occurred at biaxial stress ratio of 0.5 in the plain high strength concrete and the value were recorded 30 percent over than the strength under uniaxial condition. The failure modes of plain high strength concrete under uniaxial compression were shown as splitting type of failure but steel fiber concrete specimens under biaxial condition showed shear type failure.

• Computers and Concrete
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• v.23 no.2
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• pp.133-143
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• 2019

The paper presents the experimental investigations into the effect of ground granulated blast furnace slag (GGBFS) on the time-dependent tensile strength of concrete. The splitting and flexural tensile strength of concrete was determined at the ages of 3, 7, 28, 56, 90, 150 and 180 days using the cylindrical and prism specimens respectively for plain and GGBFS concrete. The amount of cement replacement by GGBFS was 0%, 40% and 60% on the weight basis. The maximum curing age was kept as 28 days. The results showed that the splitting and flexural tensile strength of concrete containing GGBFS has been found lower than the plain concrete at all ages and for all mixes. The tensile strength of 40 percent replacement has been found higher than the 60 percent at all ages and for all mixes. The rate of gain of splitting and flexural tensile strength of 40 percent GGBFS concrete is found higher than the plain concrete and 60 percent GGBFS concrete at the ages varying from 28 to 180 days. The experimental results of time-dependent tensile strength of concrete are compared with the available models. New models for the prediction of time-dependent splitting and flexural tensile strength of concrete containing GGBFS are proposed. The present experimental and analytical study will be helpful for the designers to know the time-dependent tensile properties of GGBFS concrete to meet the design requirements of liquid retaining reinforced and pre-stressed concrete structures.

• Proceedings of the Korea Concrete Institute Conference
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• 1992.10a
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• pp.100-105
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• 1992

While there are many researches in high-strength concrete recently, average strength required is the level of 400kg/$\textrm{cm}^2$ 28days compressive strength yet. For the effective using of high strength concrete, high strength concrete of 600 to 800kg/$\textrm{cm}^2$ 28days compressive strength must be accepted, But in this high strength concrete, due to much cement content, there are the problems of high hydration heat, high viscosity and economical efficiency. To solve these problems, it is suggested the method that replacement some of cement content as flyash up-to-dately. Therefore, the aim of this study is to develop high strength concrete of 800kg/$\textrm{cm}^2$ 28days compressive strength containing fly ash. This paper is the part I that analyze the testing results of fresh concrete in various aspects.

• Proceedings of the Korea Concrete Institute Conference
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• 1995.04a
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• pp.8-13
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• 1995

High strength ready-miced concrete with delivering time of about 90 minutes is successfully produced at ready-mixed concrete plant and placed columns and retaining walls of a tall building without any problems. The design strength of the concrete is 450 kgf/$\textrm{cm}^2$ and the required average compressive strength is 540 kgf/$\textrm{cm}^2$ according to ACI 363R-84 report with assumed coefficient of variation of 12% For the producing of good quality concrete, many laboratary and field tests are carried out. As the results of this study, the slump loss of high strength concrete is largely influenced by kinds of superplasticizer. The measured pump pressure of high strength concrete with slump of 22cm is higher than that of normal strength concrete with slump of 18cm by about 20~30% The measured average 28-day compressive strength of the concrete is 551 kgf/$\textrm{cm}^2$ and the coefficient of variation is 2.3%

• Journal of the Korea institute for structural maintenance and inspection
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• v.13 no.3 s.55
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• pp.155-163
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• 2009

The purpose of this paper is to investigate the bond strength between old and new concrete as well as flexural tensile strength of concrete. To achieve this purpose, a comprehensive experimental program has been set up and strength tests using a series of specimens have been carried out. The present study represents that the flexural bond strength between old and new concrete is much smaller than that of flexural tensile strength. The ratio of bond strength to flexural tensile strength ranged through 15~27%. It is seen that concrete-to-concrete bond strength has been affected by curing condition. Also, test results of tensile strength show that recommendation by ACI 363 committee is estimated to be more realistic than another recommendations for predicting tensile strength of concrete.

• Proceedings of the Korea Concrete Institute Conference
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• 1996.04a
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• pp.18-23
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• 1996

Since at least three-quarters of the volume of concrete is occupied by aggregate, it is not surprising that its quality is considerable importance. Not only may the aggregate limit the strength of concrete, as weak aggregate cannot porduce strong concrete, but the properties of aggregate greatly affect the durability and sructural performance of concrete. But, it is ture that aggregate strength is usually not a factor in normal concrete strength because the aggregate particle is several times stronger than the matrix and the transition zone in concrete. This study is to consider the influence the strength of concrete according to the kinds of aggregate, such as crushed river rocks, curshed rocks, high strength recycled aggregate, low strength recycled aggregate at water cement ratio 0.25. It is possible to concern the important of the mechanical role of aggegate for the high strength concrete.

• Journal of the Korea Institute of Building Construction
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• v.2 no.3
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• pp.123-130
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• 2002

Recently, it is being studied on the high strength concrete in many laboratories and being applied to the construction field actually. But non-destruction testing equation that to be proposed about normal strength concrete in Japan has been using because the systematic study results for the estimation of compressive strength of high strength concrete do nit exist. So it is essential to suggest the non-destruction testing equation for the estimation of compressive strength of high strength concrete. This is an experimental study to analyze and investigate the non-destruction testing equation for the estimation of compressive strength of high strength concrete. The results are as follows; The relation between rebound number, pulse velocity and compressive strength of high strength concrete have lower coefficient than combined method of rebound number and pulse velocity. Also new non-destructive testing equation for the estimation on the compressive strength of high strength concrete was suggested in this study, and it is considered that these equations have possibility to be applied in domestic construction field.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.10a
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• pp.241-246
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• 2000

In the strut-tie model design of structural concrete, the importance of the effective strength of concrete strut has been overlooked by many practitioners. The authors believe that the effective strength of concrete strut is an important factor not only in determining steel tie forces but also in verifying the nodal zone strength and geometric compatibility condition of a selected strut-tie model. This study evaluate the effect of the effective strength of concrete strut on structural concrete design by applying the different effective strut strengths to the strut-tie model design of a post-tensioned anchorage zone and a continuous concrete deep beam.