• KCI Concrete Journal
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• v.14 no.4
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• pp.151-159
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• 2002

This study investigates experimentally the optimum mix proportion and design factors of the stabilizing liquid used for excavation of the massive and deep slurry wall in LNG in-ground tank before pouring concrete. Considering those site conditions, the stabilizing liquid used for excavation of slurry wall has to be satisfied with some requirements including specific gravity, fluid loss, cake thickness, funnel viscosity and sand content in order to construct the safe and qualified slurry wall. For this purpose, we select materials including bentonite, polymer and dispersion agent. After performing many tests for materials and mix design process, we propose the optimum mix proportion that the upper limit ratio of bentonite is $2.0\%$, polymer is $0.1\%$ considering the funnel viscosity and dispersion agent is $0.05\%$considering the fluid loss of the stabilizing liquid. Also, we select all materials which are consisted of GTC4 as bentonite, KSTP as polymer and Bentocryl 86 as dispersion agent. Based on the results of this study, the optimum mix proportion of the stabilizing liquid is applicable to excavate the deep and massive slurry wall in LNG in-ground tank successfully.

• Computers and Concrete
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• v.21 no.3
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• pp.279-289
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• 2018

Hydration heat and thermal induced cracking have always been a fatal problem for massive concrete structures. In order to study a massive reinforced concrete wall of a storage tank for liquefied natural gas (LNG) during its construction, two mock-ups of $0.8m{\times}0.8m{\times}0.8m$ without and with metal corrugated pipes were designed based on the actual wall construction plan. Temperature distribution and strain development of both mock-ups were measured and compared inside and on the surface of them. Meanwhile, time-dependent thermal and mechanical properties of the concrete were tested standardly and introduced into the finite-element (FE) software with a proposed hydration degree model. According to the comparison results, the FE simulation of temperature field agreed well with the measured data. Besides, the maximum temperature rise was slightly higher and the shrinkage was generally larger in the mock-up without pipes, indicating that corrugated pipes could reduce concrete temperature and decrease shrinkage of surrounding concrete. In addition, the cooling rate decreased approximately linearly with the reduction of heat transfer coefficient h, implying that a target cooling curve can be achieved by calculating a desired coefficient h. Moreover, the maximum cooling rate did not necessarily decrease with the extension of demoulding time. It is better to remove the formwork at least after 116 hours after concrete casting, which promises lower risk of thermal cracking of early-age concrete.

• Magazine of the Korea Concrete Institute
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• v.15 no.2
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• pp.108-112
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• 2003

• Proceedings of the KSR Conference
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• 2004.06a
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• pp.1205-1210
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• 2004

Cracks in the underground structures are mainly observed due to internal ununiformity of thermal stresses or restraint of structural movement in associate with rapid temperature gradient. Especially, thermal cracks are known to occur easily in a massive structure, but possibility of these depend on the amount of cement applied and ratio of span to height of the structure even though the thickness is less than specification‘s. Thus, this study aims at how to control thermal cracks in a massive subway structure and figures out an optimized construction method and procedure. As results of parametric study for length, height and outer temperature for concrete placement, it is found that hydration heats were not affected by both length and height of concrete placement but thermal stresses were greatly dependent. Most effective ways of controling thermal cracks were to fit a proper ratio of length to height of concrete placement and to decrease temperature of concrete placement as much as possible.

• Journal of the Korean Society of Hazard Mitigation
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• v.6 no.2 s.21
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• pp.1-7
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• 2006

Recently, the massive concrete structures have been increasingly built in Korea. Many reinforced concrete structures have been reported to suffer from cracking in construction stages due to heat of hydration arising from mass concrete. This cracking may cause some serious durability problems and thus reduces the safety and service life of the structures. In this study, the stresses, strains, and temperatures were measured and the crack widths and crack Patterns were also observed in the footing and abutment structures. And the causes and mechanism in thermal cracking in the footing and abutment structures are thoroughly analysed. The comparisons of test results with analysis have been made. Efficient crack control techniques were developed form the experimental and analytical studies.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2004.05a
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• pp.21-25
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• 2004

The column for Steel Framed Reinforced Concrete Structure (SFRCS) and the column for Reinforced Concrete Structure (RCS) could be the most common building structure. The increasing of the need for massive space hasaffected the size of building components for supporting the massive structure. However, the changing of components size makes inefficient space of building. Hence, to meet the need for acquiring efficient space comparing the budget and cost the new structure method, Concrete Filled Tube Steel (CFT), was developed. CFT is the structure for which steel tube instead of other materials such as wood for holding concrete is used. The most benefit of this one is to help in reducing the size of the building components and local buckling because of tube steel holding concrete. For this reason, this research will examine the probability of applying CFT on construction sites by using the concrete (800kgf/$\textrm{cm}^2$) especially for CFT through the data from the real size mock-up.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.05a
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• pp.458-461
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• 2004

The column for Steel Framed Reinforced Concrete Structure (SFRCS) and the column for Reinforced Concrete Structure (RCS) could be the most common building structure. The increasing of the need for massive space hasaffected the size of building components for supporting the massive structure. However, the changing of components size makes inefficient space of building. Hence. to meet the need for acquiring efficient space comparing the budget and cost the new structure method, Concrete Filled Tube Steel (CFT), was developed. CFT is the structure for which steel tube instead of other materials such as wood for holding concrete is used. The most benefit of this one is to help in reducing the size of the building components and local buckling because of tube steel holding concrete. For this reason, this research will examine the probability of applying CFT on construction sites by using the concrete $(800kg/cm^2)$ especially for CFT through the data from the real size mock-up.

• Journal of the Korea Computer Industry Society
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• v.9 no.3
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• pp.99-104
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• 2008

The thermal stresses due to hydration heat in massive concrete structures are affected by ambient temperature and placing concrete temperature. It is needed to predict the thermal stresses considering ambient temperature and placing concrete temperature. In this study, hydration heat analyses of coping were carried out. After the maximum tensile stress was occurred at 2,75 days the crack index was increased. Therefore the possibility of crack occurrence was rare. The possibility of crack occurrence can be reduced by placing concrete temperature drop. Therefore some method to drop the placing concrete temperature may be effective to reduce the possibility of crack occurrence.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1992.10a
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• pp.67-72
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• 1992

The heat of hydration of cement causes the internal temperature rise at early age, particulary in massive concrete structures such as a footing of nuclear reactor building or a dam. As the result of the temperature rise and restraint of foundation, the thermal stress may induce cracks in concrete. Therefore, the prediction of the thermal stress is very important in the design and construction stages in order to control the cracks developed in massive concrete structures. And, in case of young concrete, creep effect by the temperature load is larger than That of old concrete. Thus the effect of creep must be considered for checking the cracks, serviceability, durability and leakage. This study is composed of two items. The first, it is to develop a finite element program which is capable of simulating the temperature history in mass concrete. The second, when the thermal stress of mass concrete structures considering creep is calculated by using the modified elastic modulus due to the inner temperature change. It is shown that the analytical results of this study is in comparably good agreement with JCI's analytical results.

• Proceedings of the Korea Concrete Institute Conference
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• 1993.04a
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• pp.194-200
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• 1993

The objective of this study is to clarify analytically the pullout behavior of axial bars from a footing. The bond stress-slip model obtained from the results by the finite element method as well as the pullout tests in massive concrete was used in order to evaluate the slip of bars from the footing. Also, the process of bond mechanism was taken into consideration on order to express the deterioration of bond stress along bars, The shape and magnitude of bond stress distribution depends upon each loading steps. Using equilibrium equation of axial force, $\tau$-S relationship and $\sigma$s-$\varepsilon$s relationship, the differential equations of each loading steps are derived. Applying both boundary and equilibrium conditions to the equations, the amount of slip could be determined. Calculated values on the basis of proposed method evaluation of the slip of bars have a good agreement with the experimental results.