• Journal of the Korea Institute of Building Construction
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• v.15 no.2
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• pp.169-175
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• 2015

Recently, a stone is preferred as a cladding materials because of its outstanding durability and luxurious character. However, because of running out of natural resources and restriction of production, it is expected that difficulty of stable supply, and thus alternative cladding materials for concrete wall is needed. Therefore, in this research, as an alternative cladding materials, exposed-aggregate concrete is studied using saccharin based retarder. For evaluating factors, changing water-to-cement ratio, dosages of saccharin-based retarder, and timing of water jet washing were tested on the surface properties of exposed-aggregate concrete. As a result, the most favorable surface performance was obtained at 0.75 day after the placing in 25% of water-to-cement ratio, and at one day after the placing in 35 and 55% of water-to-cement ratio, 1.5 day after the placing in 65% of water-to-cement ratio with $24m{\ell}/m^2$ of retarder application.

• Computers and Concrete
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• v.24 no.3
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• pp.249-258
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• 2019

In order to investigate the strength recovery of fire-damaged concrete after post-fire curing, concrete specimens were heating at $2^{\circ}C/min$ or $5^{\circ}C/min$ to 400, 600 and $800^{\circ}C$, and these exposed specimens were soaked in the water for 24 hours and following by 29-day post-fire curing. The compressive strength and split tensile strength of the high-temperature-exposed specimens before and after post-fire curing were tested. The proportion of split aggregate in the split surfaces was analyzed to evaluate the mortar-aggregate interfacial strength. After the post-fire curing process, the split tensile strength of specimens exposed to all temperatures was recovered significantly, while the recovery of compressive strength was only obvious within the specimens exposed to $600^{\circ}C$. The tensile strength is more sensitive to the mortar-aggregate interfacial cracks, which caused that the split tensile strength decreased more after high-temperature exposure and recovery more after post-fire curing than the compressive strength. The mortar-aggregate interfacial strength also showed remarkable recovery after post-fire curing, and it contributed to the recovery of split tensile strength.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.05a
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• pp.487-490
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• 2005

This study was performed to investigate the effect of ternary blended cement concrete mixed with slag cement and fly ash on the compressive strength, the resistance to chloride ion penetration and reduction of hydration heat. Each performance of ternary blended cement concrete compared with binary blended cement concrete and ordinary portland cement concrete. As a result, it was concluded that ternary blended cement concrete is suitable to mass concrete under marine environment.

• Advances in concrete construction
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• v.4 no.4
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• pp.319-332
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• 2016

In most cases strengthening reinforced concrete columns exposed to high strain rate is to be expected especially within weak designed structures. A special type of loading is instantaneous loading. Rapid loading can be observed in structural columns exposed to axial loads (e.g., caused by the weight of the upper floors during a vertical earthquake and loads caused by damage and collapse of upper floors and pillars of bridges).Subsequently, this study examines the behavior of reinforced concrete columns under rapid loading so as to understand patterns of failure mechanism, failure capacity and strain rate using finite element code. And examines the behavior of reinforced concrete columns at different support conditions and various loading rate, where the concrete columns were reinforced using various counts of FRP (Fiber Reinforcement Polymer) layers with different lengths. The results were compared against other experimental outcomes and the CEB-FIP formula code for considering the dynamic strength increasing factor for concrete materials. This study reveals that the finite element behavior and failure mode, where the results show that the bearing capacity increased with increasing the loading rate. CFRP layers increased the bearing capacity by 20% and also increased the strain capacity by 50% through confining the concrete.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.20 no.3
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• pp.349-356
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• 2022

Nuclear power plant decommissioning generates significant concrete waste, which is slightly contaminated, and expected to be classified as clearance concrete waste. Clearance concrete waste is generally crushed into rubble at the site or a satellite treatment facility for practical disposal purposes. During the process, workers are exposed to radiation from the nuclides in concrete waste. The treatment processes consist of concrete cutting/crushing, transportation, and loading/unloading. Workers' radiation exposure during the process was systematically studied. A shielding package comprising a cylindrical and hexahedron structure was considered to reduce workers' radiation exposure, and improved the treatment process's efficiency. The shielding package's effect on workers' radiation exposure during the cutting and crushing process was also studied. The calculated annual radiation exposure of concrete treatment workers was below 1 mSv, which is the annual radiation exposure limit for members of the public. It was also found that workers involved in cutting and crushing were exposed the most.

• Computers and Concrete
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• v.34 no.2
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• pp.169-178
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• 2024

To circumvent the constraints of time-consuming experimental methods, numerical simulation can be one of the most effective approaches to investigating chloride diffusion behaviors in concrete. However, except for the effect of the external environments, the transport direction of the chloride cannot be neglected when the concrete is exposed to the marine tidal zone, especially in certain areas of concrete members. In this study, based on Fick's second law, considering the effects of timevarying, chloride binding capacity, concrete stress state, ambient temperature, and relative humidity on chloride diffusion coefficient, the modified one-dimensional, two-dimensional, and three-dimensional novel modified chloride diffusion theoretical models were established through defining the current boundary conditions. The simulated results based on the novel modified multi-dimensional model were compared with the experimental results obtained from some previous pieces of literature. The comparing results showed that the modified multi-dimensional model was well-fitted with experimental data, confirming the high accuracy of the novel modified model. The experimental results in literature showed that the chloride diffusion in the corner area of the concrete structure cannot be simulated by a simple one-dimensional diffusion model, where it is necessary to select a suitable multi-dimensional chloride diffusion model for simulation calculation. Therefore, the novel modified multi-dimensional model established in this study has a stronger applicability for practical engineering.

• Computers and Concrete
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• v.2 no.4
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• pp.249-266
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• 2005

In the present paper a transient three-dimensional thermo-mechanical model for concrete is presented. For given boundary conditions, temperature distribution is calculated by employing a three-dimensional transient thermal finite element analysis. Thermal properties of concrete are assumed to be constant and independent of the stress-strain distribution. In the thermo-mechanical model for concrete the total strain tensor is decomposed into pure mechanical strain, free thermal strain and load induced thermal strain. The mechanical strain is calculated by using temperature dependent microplane model for concrete (O$\check{z}$bolt, et al. 2001). The dependency of the macroscopic concrete properties (Young's modulus, tensile and compressive strengths and fracture energy) on temperature is based on the available experimental database. The stress independent free thermal strain is calculated according to the proposal of Nielsen, et al. (2001). The load induced thermal strain is obtained by employing the biparabolic model, which was recently proposed by Nielsen, et al. (2004). It is assumed that the total load induced thermal strain is irrecoverable, i.e., creep component is neglected. The model is implemented into a three-dimensional FE code. The performance of headed stud anchors exposed to fire was studied. Three-dimensional transient thermal FE analysis was carried out for three embedment depths and for four thermal loading histories. The results of the analysis show that the resistance of anchors can be significantly reduced if they are exposed to fire. The largest reduction of the load capacity was obtained for anchors with relatively small embedment depths. The numerical results agree well with the available experimental evidence.

• Korean Journal of Construction Engineering and Management
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• v.6 no.6 s.28
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• pp.160-170
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• 2005

Because designers want to express various elevation, architectural concrete has recently paid attention to finish material and has increasingly used in the construction. architectural concrete needs more careful and professional supervision works such as controling quality of color, texture, construction plan, and design plan. none the less, It is not clear to define process and manage methods for the construction life-cycle, which causes the expense to increase and the quality to be poor. this study will analyze concrete finish method by dividing three parts which are common, exposed and architectural concrete finish method. definition and the limit of application in architectural concrete finish method will be present by comparing three methods. Throughout an interview with a staff in charge and a case study, this paper shows the requirement and the keynote of management which are divided by three steps; the design, construction and maintenance. finally, this research provides management methods of individual steps for effective construction.

• Journal of the Korea Concrete Institute
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• v.17 no.6 s.90
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• pp.871-878
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• 2005

Reinforced concrete columns exposed to fire experience severe deterioration in material properties and subsequent structural capacities. Degree of losses in structural capacity of a column due to fire-damage mainly depends on the amount of heat transferred into the column during the fire. A reasonable heat transfer model of fire-damaged reinforced concrete column needs to take into account the heat-dependent nonlinear properties of heat conductivity and heat capacity of concrete as well as the evaporation of moistures in a section during the fire. Compared to the previously suggested models, the developed model in this study has included all these parameters in its numerical expressions based on explicit finite difference method. The developed model could predict the temperature changes with a reasonable accuracy for the columns exposed to fire.

• Proceedings of the KIEE Conference
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• 2005.07a
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• pp.402-404
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• 2005

This paper represents the amapcity calculation method of power cables installed in a concrete construction above a bridge which is exposed to solar radiation.