• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.5
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• pp.34-40
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• 2014

High-performance fiber-reinforced cement composite (HPFRCC) shows very high autogenous shrinkage, because it contains a low water-to-binder ratio (W/B) of 0.2 and high fineness admixture without coarse aggregate. Thus, it needs a method to decrease the cracking potential. Accordingly, in this study, to effectively reduce the shrinkage of HPFRCC, a total of five different ratios of SRA (1% and 2%), EA (5% and 7.5%), and a combination of SRA and EA (1% and 7.5%) were considered. According to the test results of ring-test, a combination of SRA and EA (1% and 7.5%) showed best performance regarding restrained shrinkage behavior without significant deterioration of compressive and tensile strengths. This was also verified by performing modified drying shrinkage crack test.

• Journal of the Korea institute for structural maintenance and inspection
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• v.7 no.1
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• pp.173-179
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• 2003

Currently, in the mix design of high strength concrete, cement content depend on the target slump which is fixed with tests. However this cause high content cement use because it is based on the mix design of normal strength concrete. Also, comparatively high content cement might decrease the durability of the concrete. Therefore, in this study, we investigated proper cement content satisfying durability, workability, compressive strength, and reviewed use of admixtures, proper sand-aggregate ratio to the cement content. The results indicate that cement content ranging $370{\sim}550kg/m^3$ did not affect the compressive strength. The field workers should consider durability, workability as well as compressive strength for determining the optimal cement content in the mix design of the high strength concrete.

• The Journal of the Korea Contents Association
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• v.15 no.3
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• pp.415-426
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• 2015

For a long time, evaluation of soundness and strength in concrete has been performed through ultrasonic velocity(UV), which is essential work in field assessment. Porosity in concrete is a major parameter indicating durability and strength, and UV passing concrete depends on porosity variation. In this paper, a modeling on UV through concrete is carried out considering porosity and the results are verified with those from test. Additionally UV in concrete under compression/tension loading condition is measured and UV modeling with loading condition is performed. Up to 50% of loading ratio, UV slightly increases and greatly drops at peak load in compression region, however it fluctuates in tensile region due to micro cracking in matrix. The proposed model shows a reasonable agreement with test results in control and compression region, and needs modification for tensile region considering micro cracks and local aggregate interlocking.

• Magazine of the Korean Society of Agricultural Engineers
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• v.33 no.2
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• pp.61-72
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• 1991

This study was carried out to research the strength drop of concrete in dry environment. The mixing ratio of cement-fine aggregate was 1: 1, 1 : 2, 1: 3 and 1 : 4. The curing was compared standard curing with dry curing immediately after casting. It is analysis of strength change by water-proof mixing. The curing age of cement mortar was 3days, 7days, l4days and 28days. The result obtained from this study are summarized as follows. 1. The compressive and bending strength change by increasing the curing age, dry curing mortar the increasing rate of strength was decreased than standard curing mortar. 2. The compressive and bending strength change in early curing, strength difference between standard curing mortar and dry curing motar was gradually closed by increasing the W/C. 3. The dry curing mortar was decreased than standard curing mortar in decreasing rate of compressive and bending strength by increasing the W/C. 4. The compressive strength of water-proof mortar in early curing, liquid water-proof mortar was shown high strength in dry curing than standard curing. The powder and liquid water-proof mortar have a small effect in dry environment. The liquid water-proof mortar was high strength without relation change of curing age in dry environment than standard curing. 5. The compressive strength of liquid water-proof mortar in poverty mix, dry curing was shown high strength than standard curing. 6. The bending strength was increased than compressive strength by decreasing the volume of cement in early curing. The increasing rate of bending strength was decreased to compressive stength by increasing the curing age.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.445-448
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• 2008

It is essential that concrete component is made up with aggregate, cement and water. But today, Public concern is increasing of a variety structure and ocean environmental, resource recycle. Also, According to heat of hydration rising, Concrete is make a causative of concrete-crack. Concrete-crack cause a falling-off in quality of concrete. consequently, High-performance concrete is evaluated by concrete material properties and carbonation resistance with different admixture(fixing fly-ash 20%), granulated blast furnace slag replacement ratio (30%, 45%) different W/B (26%, 30%, 34%) and XRD(X-ray Diffraction) analysis.

• Journal of the Korea Institute of Building Construction
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• v.15 no.2
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• pp.161-167
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• 2015

Nowadays, all the world face to the global warming problems due to the emission of $CO_2$. From the previous studies, recycled aggregates were used as an alkali activator in blast furnace slag to achieve zero-cement concrete, and favorable results of obtaining strength were achieved. In this study, gypsum and incineration waste ash were used as the additional alkali activation and effects of the gypsum and incineration waste ash to enhance the performance of the mortar were tested. Results showed that although the replacement ratio of 0.5% of incineration waste ash and 20% of anhydrous gypsum resulted in the low of mortar at the early age, while it improved the later strength and achieved the similar strength to that of conventional mortar (at 91 days).

• KSCE Journal of Civil and Environmental Engineering Research
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• v.7 no.2
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• pp.59-68
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• 1987

Several series of fracture tests were conducted to explore the fracture characteristics and to determine the fracture energy of concrete. A stable three-point bend test was employed to generate the load-deflection curves. The fracture energy may then be calculated from the area under the complete load-deflection curve. The initial notch-to-beam depth ratio (${\alpha}_0$/H) was varied from zero to 0.6. The prediction formula for the fracture energy of concrete is also derived and is found to depend on the tensile strength and aggregate size. The proposed fracture energy formula can be used for the fracture analysis of concrete structures. The present study also devises an equivalent crack length concept to predict the maximum failure loads of concrete beams. A simple formula for the equivalent crack length is proposed.

• Journal of the Korea Institute of Building Construction
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• v.15 no.3
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• pp.257-263
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• 2015

In this study, the quality of blast furnace slag and the engineering properties of recycled aggregate based mortar with variable replacement of blast furnace slag have been focused. Blast furnace slag(BS) manufactured in various areas in Korea were prepared for this study. For the investigation results, 4 types(among the all of 9 types) of the experimental results were identified as below the standard level when using blast furnace slag chosen from different factories. Especially the particle size of the blast furnace slag was considered as the largest problem. When using BS in the recycled aggregates based mortar, the increase amount of blast furnace slag, increased the fluidity but delayed the setting time and decreased strength at early age. Based on the relationship of the amount of BS and the engineering properties of mortar, this study found that the amount of $SO_3$ and L.O.I affect the setting time, 3 days strength and 91 days strength to the certain standard level.

• Journal of the Korea Concrete Institute
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• v.14 no.1
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• pp.67-75
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• 2002

For the design of concrete structures in the serviceability limit state, the uniaxial static modulus of elasticity may be a most important parameter. In particular, this may be so just for a deflection control of the structure. Even in new concrete codes, however, the elastic modulus is normally presented on the form of general empirical relationships with the compressive strength and density of concrete. Normally, there is a large uncertainty associated with the general equations obtained by regression. Thus, in a typical plot of static modulus of elasticity vs. compressive strength, a large scatter can be observed at same strength. The aim of this study is to present the method for obtain the maximum modulus of elasticity at same compressive strength. In the present paper report the effects of mix ingredients on the modulus of elasticity of high-strength concrete. The test of 284 cylinder specimens arc conducted for type I with 11 ％ replacement of fly-ash cement concretes. Different water-hinder ratio, amounts of water and coarse aggregate as variables were investigated. And also analyzed it statistically by using SAS.

• Journal of the Korea Institute of Building Construction
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• v.3 no.2
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• pp.129-134
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• 2003

In this research, we used fly-ash and blast-furnace slag as substitute material of cement and fine aggregate, and we, through experiments, researched and analyzed the features of high-flowable concrete added high efficiency AE water reduction agent. The results are below. 1. Liquefaction generally presented high-slump flow value; on the other hand, partial segregation was observed in case of mixing proportion with 65 cm slump flow and above. This segregation was partially improved in accordance with mixing admixture. 2. Compressive strength according to mixing admixture and increasing mixing ratio of fly-ash were subject to be declined when it was initially cast-in, but its gap was improved when time was fully passed. 3. After mixing blast-furnace slag and fly-ash as substitute material, the result showed that the modulus of elasticity against freezing & melting was improved according to mixing blast-furnace slag and also increased in accordance with increasing pulverulent-body volume. 4. According to increasing the mixing volume of fly-ash, the durability factor was deteriorated because compressive strength became lower as well as air content was decreased when it was initially case-in. 5. The minimum air content to secure durability was 3.7%, for that reason, we had better secure admixture such as air entraining agent when cast-in high-flowable concrete.