• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.701-704
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• 2006

Recently, the attention is paid to the problem of thermal crack by hydration heat according to the increase of high strength and mass concrete structures. At this point, various research has been carried out for the control of hydration heat in high strength and mass concrete. As a part of the research, the application of Low Heat Technology (LHT) for the control of thermal crack by hydration heat was investigated in this study. To investigate the application, it was selected LHT which can reduce hydration heat of concrete with effect in series I and II. Also, it was investigated the characteristics of hydration heat generation of low heat concrete using LHT with binder types in seriesIII.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.709-712
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• 2006

It is necessary to develop a new technology for controling thermal cracking by hydration heat according to the increase construction of massive concrete structures, high strength concrete and early strength concrete. Therefore, it was investigated the characteristics of hydration heat generation of low heat concrete using hydration heat reducing admixtures in this study. To investigate the performance of hydration heat reducing admixtures, it was evaluated hydration heat according to the kind and replacement ratio of phase change material series I, II and the way of using hydration heat reducing admixtures in series III.

• Journal of the Korea Concrete Institute
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• v.14 no.2
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• pp.249-256
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• 2002

High performance concrete is prone to large autogenous shrinkage due to its low water to binder ratio (W/B). The autogenous shrinkage of concrete is caused by self-desiccation as a result of water consumption by the hydration of cement. In this study, the autogenous shrinkage of high performance concrete with and without fly ash was Investigated. The properties of fresh concrete, slump loss, air content, and flowability as well as the mechanical properties, compressive strength and modulus of elasticity, were also measured. Test results was shown that the autogenous shrinkage of concrete increased as the W/B decreased. For the same W/B, the autogenous shrinkage of high strength concrete with fly ash was considerably reduced although the development of its compressive strength was delayed at early ages. Furthermore, the autogenous shrinkage and compressive strength of high strength concrete were more rapidly developed than those of normal strength concrete. It was concluded that fly ash could improve the quality of high strength concrete with respect to the workability and autogenous shrinkage.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.05b
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• pp.29-32
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• 2005

In this study, the experiment was carried out to investigate and analyze the strenth properties and flowability of ultra-high strength concrete accroding to types of mineral admixtures. The main experimental variables were water/binder ratio 25.0, 27.5 and 30.0$\%$, water content 155, 160, 165, and 170kg/$m^{3}$ and mineral admixtures such as fly ash, silica fume and meta kaolin. According to the test results, the principle conclusions are summarized as follows. 1) In case of using admixtures, superplasticizer amount need more than plain concrete. 2) According to kinds of admixtures, the viscosity of concrete show much difference. 3) The compressive strength of concrete that use admixtures becomes low in early-age strength, but appeared by higher than plain concrete in long-term strength. 4) Meta kaolin is excellent in side but has viscosity enlargement efficiency a little. But, problem estimates that is not to make design strength 600 and 700kgf/$cm^{2}$ if use mixing condition with water-binder ratio properly.

• Advances in materials Research
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• v.12 no.4
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• pp.331-349
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• 2023

Foam concrete can be considered as environmental friendly material due to its low weight, its minimal cost and a possibility to add waste materials in its production. This paper investigates the possibility of producing foam concrete with waste glass as powder and aggregate. Then, the effect of using waste glass on strength and drying shrinkage of foam concrete was examined. Also, the effect of incorporating polypropylene fibers (12 mm length and proportion of 0.5% of a mix volume) on distribution of waste glass as coarse particles within 1200 kg/m³ foam concrete mixes was evaluated. Waste glass was used as powder (20% of cement weight), as coarse particles (25%, 50% and 100% instead of sand volume) and as fine particles (25% instead of sand volume). From the results, the problem of non-uniform distribution of coarse glass particles was successfully solved by adding polypropylene fibers. It was found that using of waste glass as coarse aggregate led to reduce the strength of foam concrete mixes. However, using it with polypropylene fibers in combination helped in increasing the strength by about 29- 50% for compressive and 55- 71% for splitting tensile and reducing the drying shrinkage by about (31- 40%). In general, not only the fibers role but also the uniformly distributed coarse glass particles helped in improving and enhancing the strength and shrinkage of the investigated foam concrete mixes.

• Explosives and Blasting
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• v.16 no.4
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• pp.18-28
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• 1998

Effects of blasting vibrations on curing concrete have not been well studied. As a result, unreasonable and strong blasting vibration constraints have been placed on blasting when it occur in the vicinity of curing concrete. To study the effects of blasting on curing concrete blocks of $33.3{\times}27.7{\times}16.2cm$ were molded and placed on the quarry. Several sets of concrete blocks were subjected separately to peak vibrations of 0.25, 0.5, 1.0, 5.0 and 10cm/sec. The impulses of blasting vibrations were applied with thirty-minute intervals. Along with unvibrated concrete blocks, the vibrated concrete samples cored with 60.3mm in diameter were measured for elastic moduli, sonic velocity and uniaxial compressive strength. Test results can be summarized as follows; 1. The blasting vibrations between 6 and 8 hours after pour generally lowered on the uniaxial compressive strength of the concrete. 2. A low blasting vibration of 0.25cm/sec did not affect the uniaxial compressive strength. As the magnitude of the blasting vibration increases, compressive strength of concrete is decreased. 3. Physical properties of the P-wave velocity, Young’s modulus, and Poisson's ratio showed a weakly decreasing trend in the concrete blocks vibrated between 6 and 8 hours after pour.

• Tunnel and Underground Space
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• v.5 no.2
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• pp.134-143
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• 1995

Effects of blasting vibrations on curing concrete have not been well studied. As a result, unreasonable and strong blasting vibration constraints have been placed on blasting when it occurs in the vicinity of curing concrete. To study the effects of blasting on curing concrete blocks of 33.3X27.7X16.2 cm were molded and placed on the quarry. Several sets of concrete blocks were subjected separately to peak vibrations of 0.25, 0.5. 1.0, 5.0, and 10cm/sec. The impulses of blasting vibrations were applied with thirty-minute intervals. Along with unvibrated concrete blocks, the vibrated concrete samples cored with 60.3 mm in diameter were measured for elastic moduli, sonic velocity and uniaxial compressive strength. Test results can be summarized as follows; 1. The blasting vibrations between 6 and 8 hours after pour generally lowered on the uniaxial compressive strength of the concrete. 2. A low blasting vibration of 0.25 cm/sec did not affect the uniaxial compressive strength. As the magnitude of the blasting vibration increases, compressive strength of concrete is decreased. 3. Physical properties of the P-wave velocity, Young's modulus, and Poisson's ratio showed a weakly decreasing trend in the concrete blocks vibrated between 6 and 8 hours after pour.

• Magazine of korean Tunnelling and Underground Space Association
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• v.1 no.1
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• pp.81-87
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• 1999

Effects of blasting vibrations on curing concrete have not been well studied. As a result, unrealistic and costly blasting vibration constraints have been placed on blasting when it occurs in the vicinity of curing concrete. To study the effects of blasting, concrete blocks of $30\times20\times20cm$ were molded and placed on the quarry Different sets of concrete blocks were subjected to peak vibrations of 0.25, 0.5, 1.0, 5.0, and 10cm/sec. The impulses of blasting vibrations were applied at thirty minutes intervals . Along with unvibrated concrete blocks, the vibrated concrete samples with 60.3mm in diameters were measured for elastic moduli, sonic velocity and uniaxial compressive strength. Test results can be summarized as follows : 1) The blasting vibrations between 6 and 8 hours after pour generally have exerted bad influences on the uniaxial compressive strength of the concrete 2) Under low vibration of 0.25cm/sec variations of the uniaxial compressive strength were not shown. As the magnitudes of blasting vibration increased, compressive strength of concrete decreased. But under the vibrations between 5 and 10cm/sec decreases in strength were almost same. 3) Physical properties of the p-wave velocity, Young's modulus, and Poisson's ratio appeared to decrease for the concrete blocks subjected to vibration for 6 to 8 hours.

• Proceedings of the Korea Concrete Institute Conference
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• 1992.10a
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• pp.185-190
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• 1992

ACI318-89 Recommended that when the specified compressive strength of concrete in a column is greater than1.4 times that specified for a floor system, top surface of the column concrete shall extend 2ft(600mm)into the slab from the face of column to avoid unexpected brittle failure. The major variables are extension distance, flexural strength ratio(Mr), and shear reinforcement ratio(Vs). Test results are as follows ; (1) The failure modes of specimens under cyclic loading were concentrated at critical region from beam-column joint face. (2) Ductility index($\mu$f) were increased with increasing of shear confinement ratio and flexural strength ratio. (3)The specimens with 2ft extension distance showed more ductility than the specimens with 1ft extension distance.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.533-536
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• 2001

When fresh concrete is exposed to low temperature, the concrete may suffer frost damage due to freezing at early ages and strength development may be delayed. One of the solution methods for resolving these problems is to reduce freezing temperature of concrete by the use of chemical admixture called Accelerators for freezing resistance. In this study, we investigate the effect on strength development of cement mortar using accelerators for freezing resistance with the variance curing condition. As the result of this study, the mortar using accelerators for freezing resistance show that continuously strength development in curing condition of -5$^{\circ}C$. And compressive strength under the variance temperature condition was higher than fixed temperature condition in same maturity.