• International Journal of Concrete Structures and Materials
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• v.5 no.1
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• pp.3-10
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• 2011

Theoretical models for prediction of the mechanical properties of cement mortar are developed based on the morphology and interactions of cement hydration products, capillary pores and microcracks. The models account for intermolecular interactions involving the nano-scale calcium silicate hydrate (C-S-H) constituents of hydration products, and consider the effects of capillary pores as well as the microcracks within the hydrated cement paste and at the interfacial transition zone (ITZ). Cement mortar was modeled as a three-phase material composed of hydrated cement paste, fine aggregates and ITZ. The Hashin's bound model was used to predict the elastic modulus of mortar as a three-phase composite. Theoretical evaluation of fracture toughness indicated that the frictional pullout of fine aggregates makes major contribution to the fracture energy of cement mortar. Linear fracture mechanics principles were used to model the tensile strength of mortar. The predictions of theoretical models compared reasonably with empirical values.

• Journal of the Korean GEO-environmental Society
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• v.14 no.4
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• pp.5-13
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• 2013

The water leakage of reservoir embankment usually occurs around channelling pipes, which gives little influence on the embankment in a normal state. However, the embankment can be destroyed when the water level of reservoir increases with heavy rain and the rainy season in summer. Investigating the water vein and its path is therefore very important from the viewpoint of disaster prevention and embankment maintenance. The water leakage in dams and levees where the channelling pipes are working as weak zone was analyzed by using both numerical simulation and experimental method in this study. To detect the water leakage, an electrical resistivity survey was used and investigated for its' usability. The numerical results show the size and location of weak zone increases the importance of selection of electrode spacing. The leakage experiments of model embankment present the best result is obtained under the conditions of electrode spacing of 0.3m and dipole-dipole array. By studying the water leakage in dams and levees, the electrical resistivity survey is observed it is a very useful method to predict the leakage.

• Journal of the Korea Concrete Institute
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• v.22 no.2
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• pp.209-217
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• 2010

Recently, some mathematical models for the prediction on progress of carbonation of concrete were reported. These models take account for $CO_2$ diffusion and chemical reaction between $Ca(OH)_2$ and $CO_2$. Based on the assumption that $CO_2$ diffuses in the carbonation zone and reacts with $Ca(OH)_2$ at the outer face of carbonation zone and non-carbonation zone. In this study, a mathematical model to predict the progress of carbonation of concrete has been established based on the reducing concentration of $Ca(OH)_2$ in the carbonation progress zone, where $Ca(OH)_2$ reacts with $CO_2$ and $Ca(OH)_2$ and $CaCO_3$ coexist. Also, the prediction model of carbonation progress rate of concrete using the air permeability coefficient regarding to $CO_2$ diffusion is developed. As a result of this study, an expression, the model equation is obtained for the prediction of carbonation based on the time and interaction velocity between $CO_2$ and Ca(OH)$_2$ dependent air permeability coefficient. The prediction by the model satisfied the experimental data of the accelerated carbonation for painted concrete. Consequently, the model can predict the rate of carbonation and the potential service life of concrete structure exposed to atmosphere.

• Computers and Concrete
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• v.21 no.4
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• pp.471-484
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• 2018

Refined analysis depicting mass transportation and physicochemical reaction and reasonable computing load with acceptable DOFs are the two major challenges of numerical simulation for concrete durability. Mesoscopic numerical simulation for chloride diffusion considering binder, aggregate and interfacial transition zone is unable to be expended to the full structure due to huge number of DOFs. In this paper, a multiscale approach of combining both mesoscopic model including full-graded aggregate and equivalent macroscopic model was introduced. An equivalent conversion of chloride content at the Interfacial Transition Layer (ITL) connecting both models was considered. Feasibility and relative error were discussed by analytical deduction and numerical simulation. Case study clearly showed that larger analysis model in multiscale model expanded the diffusion space of chloride ion and decreased chloride content in front of rebar. Difference for single-scale simulation and multiscale approach was observed. Finally, this paper addressed some worth-noting conclusions about the chloride distribution and rebar corrosion regarding the configuration of rebar placement, rebar diameter, concrete cover and exposure period.

• Journal of Ocean Engineering and Technology
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• v.24 no.6
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• pp.16-22
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• 2010

In this paper, the diffraction problems for fixed offshore structures are solved using a hybrid scheme. In this hybrid scheme, potential-based solutions and the Navier-Stokes-based finite volume method (FVM) with a volume-of-fluid (VOF) method are combined. We introduce a buffer zone for efficient wave-making and damping. In this buffer zone, the near field solution from FVM-VOF is gradually changed to Stokes' 2nd order wave solutions. Three different models, including the truncated cylinder, sphere, and wigleyIII model, are numerically investigated in regular waves with a wave steepness of 1/30. The efficiency and accuracy of the hybrid scheme are numerically validated from results using different domain sizes and buffer zones. The wave exciting forces from the FVM-VOF simulations are compared with experiments and potential-based solutions from the higher-order boundary element method (HOBEM). This comparison shows good agreement between the hybrid scheme and potential-based solutions.

• 한국지구물리탐사학회:학술대회논문집
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• 2004.06a
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• pp.182-188
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• 2004

In view of the circular geometry of the Serra da Cangalha impact crater, we have carried out a 3D forward modeling computation for twenty-five MT data in order to obtain the 3D resistivity forward model for the crater region. The 3D resistivity forward model revealed a five-layer model, showing a significant reduction in the basement resistivity. We suggest that this, perhaps, could be due to the structural disturbances that have been caused by the meteorite impact on the crater about 220 million years ago resulting in brecciation, fracturing, alteration and shocked zone filled with fluids. Also, the sensitivity analysis of the 3D model chosen indicates that 3D models having a crater diameter greater than 151 are inconsistent with our data because the 3D model responses are very sensitive to changes in the diameter beyond 15 km. This analysis also reveals that, the depth limits (for the 3D body) causing the anisotropic effects seen on some of our apparent resistivity curves maximally does not extend beyond 1.2 km depth.

• Korean Journal of Crystallography
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• v.3 no.1
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• pp.53-66
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• 1992

Extensive research has been perform성 on the property-microstructure-process condition relations of thin films. The various proposed models are mainly based on physical vapor deposition processes. Especially the study on the surface condition of substrates in Zone 1 with low surface mobility has not been sufficient. In this study, therefore, we discussed the mochological changes of TiN films deposited by plusma enhanced chemical vapor deposition process with substrates of different composition and micro-rorghness, and compared it with the Structure Zone Model. We could find out that the growth rate of films increased and micro-grain size decreased with the increase in micro-roughness, but it does not improve the mechanical properties because of many imperfections like voids, micro-cracks, stacking faults, etc. This means that, in these deposition conditions, the increase in shadowing diffect is more effective than the increase in nucleation sites on the growth of films due to the increase in substrate roughness.

• Proceedings of the KSR Conference
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• 2007.05a
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• pp.1056-1061
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• 2007

Railroad roadbed was consisted into structure types that earthwork, tunnel, bridge and joint sections. Joint section was affected a large factor confidence and safety of the train running by stiffness transition zone that track substructure stiffness change section as like between tunnel and earthwork from ballast track to concrete track. These problems are the results of increased dynamic wheel loads, which also lead to wear and tear on vehicle components and contribute to poor ride quality. The study presented in this paper was conducted on model test by using Wheel Moving Loading System.

• Journal of Environmental Science International
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• v.11 no.10
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• pp.1039-1044
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• 2002

In this study, breakwater model which has several outlet pipes to discharge water is settled in the experimental open channel and mean velocity distributions of multi wall jet are measured. The length of zone of flow establishment of wall jet is shorter than that of free jet and decay rate of jet centerline longitudinal velocity along x is linear in $0.3{leq}x/I_p{leq}17$. The rate of vertical width and lateral width spreading of multi wall jet is respectively 0.0753, 0.157.

• Journal of Korean Port Research
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• v.6 no.1
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• pp.69-91
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• 1992

A new type of horizontal submerged break water or fixed structure to control waves near coastal area is introduced to focus wave energy before or behind it. Intentionally, the water depth near the structure is changed gradually to get a refraction and diffraction effect. The concentration of wave energy due to the structure was analyzed for the selected design of structure. The shape of the submerged structure in consideration is a circular combined with elliptical curve not to cause reflection of waves at the extreme edge of the structure but cause wave scattering. The direction of the structure against the incident wave is changed easily in the model Applying a regular wave train the following were examined. 1) whether a crescent plain submerged structure designed by the wave refraction theory can concentrate wave energy at a focal zone behind and before it without wave breaking phenomenon. 2) Location of maximum wave amplification factor in terms of the incident wave direction, wave period, etc. In any event the study would contribute to control waves near coastal area and to protect a beach from erosion without interruption of ocean view it is an useful study for the concentration of wave energy efficiently with the increase of wave height.