• Korean Journal of Construction Engineering and Management
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• v.11 no.6
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• pp.111-121
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• 2010

As the customer's interest for sidewalk block in the street or apartment complex is increasing, the materials of block which had been a concrete block exclusively are varied to clay paver, native rock and wood etc. Especially, the sales volume of clay paver which is environment-friendly and ergonomic is dramatically increasing every year with two digits growth rate, however, many problems like "Edge Cracking" "Freezing Breakage" "Bending Breakage" "Joint Gap" are happening frequently within a couple of hours after installation due to the durabilities. Because of the characteristics of Ceramic products, clay pavers are very easy to be broken when they are bumped against each other. In addition, they are relatively fragile by a freezing expansion breakage when exposed to water due to hydrophilic property as well as the intensity and absorptance of the products are varied with small difference from the production process such as production equipment and process control. Therefore, it costs a lot of money to repair the breakdown unless production and installation is carried out according to the strict criteria of the quality control. In this study, the symptoms of breakdown frequently happened in clay paver are classified by each type and finally the solution for this problem in the production of brick, installation and criteria of quality control through compressive strength and absorptance test is suggested.

• Journal of the Korea Concrete Institute
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• v.15 no.4
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• pp.594-605
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• 2003

Pinching is an important property of reinforced concrete member which characterizes its cyclic behavior. In the present study, numerical studies were performed to investigate the characteristics of pinching behavior and the energy dissipation capacity of flexure-dominated reinforced concrete members. By investigating existing experiments and numerical results, it was found that flexural pinching which has no relation with shear action appears in RC members subject to axial compression force. However, members with specific arrangement and amount of re-bars, have the same energy dissipation capacity regardless of the magnitude of the axial force applied even though the shape of the cyclic curve varies due to the effect of the axial force. This indicates that concrete as a brittle material does not significantly contribute to the energy dissipation capacity though its effect on the behavior increases as the axial force increases, and that energy dissipation occurs primarily by re-bars. Therefore, the energy dissipation capacity of flexure-dominated member can be calculated by the analysis on the cross-section subject to pure bending, regardless of the actual compressive force applied. Based on the findings, a practical method and the related design equations for estimating energy dissipation capacity and damping modification factor was developed, and their validity was verified by the comparisons with existing experiments. The proposed method can be conveniently used in design practice because it accurately estimates energy dissipation capacity with general design parameters.

• Journal of the Korea Concrete Institute
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• v.27 no.3
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• pp.245-252
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• 2015

As people have more interest in environment-friendly structures recently, many researchers are actively researching non-sintered cement in Korea and other countries. Non-sintered cement shows various characteristics of its reaction products and hardeners, depending on the kind of alkali activators. Thus, this study manufactures ground granulated blast furnace slag based non-sintered cement binder by using circulating fluidized bed combustion ash, which is a kind of industrial byproduct, as a stimulant, and investigated its hardening characteristics and hydration, depending on the rate of circulating fluidized bed combustion ash. Besides, this study investigated its insulation property according to the weight lightening of non-sintered cement. As a result, ettringite and C-S-H were mainly formed in the hydration, and it was possible to manufacture a non-sintered cement hardener over 50 MPa. Lastly, it was possible to manufacture a non-sintered cement hardener in a thermal conductivity level of $0.127W/m{\cdot}K$ when the compressive strength was 10 MPa for weight lightening.

• Geomechanics and Engineering
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• v.19 no.5
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• pp.421-434
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• 2019

It is of great significance to study the mechanical properties and failure mechanism of the defected rock for geological engineering. The defected sandstone modeling with power-law distribution of pre-cracks was built in this paper by Particle Flow Code software. Then the mechanical properties of sandstone and the corresponding failure process were meticulously analyzed by changing the power-law index (PLI) and the number of pre-cracks (NPC). The results show that (1) With the increase of the PLI, the proportion of prefabricated long cracks gradually decreases. (2) When the NPC is the same, the uniaxial compressive strength (UCS) of sandstone increases with the PLI; while when the PLI is the same, the UCS decreases with the NPC. (3) The damage model of rock strength is established based on the Mori-Tanaka method, which can be used to better describe the strength evolution of damaged rock. (4) The failure mode of the specimen is closely related to the total length of the pre-crack. As the total length of the pre-crack increases, the failure intensity of the specimen gradually becomes weaker. In addition, for the specimens with the total pre-crack length between 0.2-0.55 m, significant lateral expansion occurred during their failure process. (5) For the specimens with smaller PLI in the pre-peak loading process, the concentration of the force field inside is more serious than that of the specimens with larger PLI.

• Journal of the Korea Concrete Institute
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• v.24 no.5
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• pp.543-551
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• 2012

Road pavements in Korea generally show shorter service life than the predicted one. There are many reasons for this phenomenon including increased traffic load and other attacks from exposure conditions. In order to extend a service life and upgrade the pavement, a new multi-functional composite pavement system is being developed in Korea. This study is to investigate the performances of fiber-reinforced lean concrete for pavement base. This study considered mineral admixtures of fly ash and reject ash. The reject ash is defined as ash that does not meet the specifications for fly ash so that it cannot be used as a supplemental material for cement replacement. Due to the inherent property of lean concrete, compaction during the fabrication of specimens is a key factor. Therefore, this study suggests an appropriate compaction method. From the test results, the compressive strengths of the concrete satisfied the required limit of 5 MPa at 7 days. When a compaction roller was used to mimic actual field conditions, the strength development seemed to be influenced by the compaction energy rather than hydration of cement itself.

• Journal of the Korea Institute of Building Construction
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• v.17 no.5
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• pp.411-418
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• 2017

This study classified oyster shells that produced as a industrial waste into 3 distribution by washing, drying and processing them. Mortar specimens with a constant ratio by using this to substitute fine aggregates were made, and the specimens were heated under the heating conditions of $300^{\circ}C$, $600^{\circ}C$ and $900^{\circ}C$ based on the 28-day age. On the age of 28 days, the plain flexural strength was found to be 9.2MPa, and in O 0.15, it was shown to be 4.4~7.9MPa depending on the substitution rate. It was found to be 4.4~7.7MPa in O 1.2~2.5 depending on the substitution rate, and last but not least, it was shown to be 6.1~8.8MPa in case of O 2.5~5.0 depending on the substitution rate. In case of the compressive strength of the 28-day age, it showed the difference of 23.6~43.2MPa in O 0.15 depending on the substitution rate, and 20.4~45.1MPa in O 1.2~2.5 depending on the substitution rate, and last but not least, 17.1~40.4MPa in case of O 2.5~5.0. As a result of measuring the residual strength through heating, in case of substituting fine aggregates less than O 0.15 by 100%, it showed the lowest strength reduction ratio, and it is expected that the heat-resisting property could be achieved through processing and proper mixing of oyster shells through these results.

• Applied Chemistry for Engineering
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• v.18 no.4
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• pp.376-380
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• 2007

Used polyurethane (PU) was chemically degraded by the treatment with flame retardants such as tris(1,3-chloro-2-propyl) phosphate (TCPP), triethyl phosphate (TEP), and trimethyl phosphate (TMP). Analysis of FT-IR and P-NMR showed that the degraded products (DEP) contained oligourethanes. Rigid polyurethane foam was produced using the DEP as flame retardants. The flammability and thermal stability of recycled rigid polyurethane were investigated. The mechanical properties such as compressive strength of recycled polyurethane were also studied. The recycled polyurethane reduced flammability and enhanced thermal stability over intrinsic polyurethane. Mechanical strength of recycled polyurethane also shows as high as that of intrinsic polyurethane. In order to evaluate flame retardant properties of the recycled polyurethane foams with various amounts of DEP, heat release rate (HRR) of the foam was measured by cone calorimeter. Scanning electron micrograph of recycled PU showed a uniform cell morphology as a intrinsic PU.

• Applied Chemistry for Engineering
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• v.7 no.3
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• pp.597-604
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• 1996

Resin-type neutron shielding materials, KNS-115A, 115B and 115C have been fabricated to be used for spent fuel shipping cask. The base material is epoxy resin, and polypropylene, aluminium hydroxide and boron carbide are added. These shielding materials offer good fluidity at processing, which makes it possible to apply this resin shield to complicated geometric shapes such as shipping cask. Several measurements were made for the shielding materials to evaluate the shielding property, combustion characteristics, fire resistance, thermal and mechanical properties. The neutron shielding ability of the shielding materials is estimated to be better than that of foreign's shielding material, NS-4-FR, due to higher hydrogen atomic density. Other properties of the shielding materials are as follows: Onset temperatures; $267{\sim}270^{\circ}C$, thermal conductivities; $0.62{\sim}0.72W/m{\cdot}K$, combustion characteristics; <$800^{\circ}C$, ATB(average time of burning); <5sec, AEB(average extent of burning) ; <5mm, tensile strengths; $2.3{\sim}3.0kg/mm^2$, compressive strengths; $5.3{\sim}13.3kg/mm^2$, flexural strengths; $4.4{\sim}5.4kg/mm^2$.

• Clean Technology
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• v.24 no.3
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• pp.239-248
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• 2018

In this study, pervaporation experiments of water, ethanol and IPA (Isopropyl alcohol) single components and water/ethanol, water/IPA mixtures were carried out using zeolite 4A membranes developed by Fine Tech Co. Ltd. Those membranes were fabricated by hydrothermal synthesis (growth in hydrothermal condition) after uniformly dispersing the zeolite seeds on the tubular alumina supports. They have a pore size of about $4{\AA}$ by ion exchange of $Na^+$ to the LTA structure with Si/Al ratio of 1.0, and shows strong hydrophilic property. Physical characteristics of prepared membranes were evaluated by using SEM (surface morphology), porosimetry (macro- or meso- pore analysis), BET (micropore analysis), and load tester (compressive strength). Pervaporation experiments with various temperature and concentration conditions confirmed that the zeolite 4A membrane can selectively separate water from ethanol and IPA. Water/ethanol separation factor was over 3,000 and water/IPA separation factor was over 1,500 (50 : 50 wt%, initial feed concentration). Pervaporation behaviors of single components and binary mixtures were predicted using ACM (activity coefficient model), GMS (generalized Maxwell Stefan) model and DGM (Dusty Gas Model). The adsorption and diffusion coefficients of the zeolite top layer were obtained by parameter estimation using GA (Genetic Algorithm, stochastic optimization method). All the calculations were carried out using MATLAB 2018a version.

• Journal of the Korean Recycled Construction Resources Institute
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• v.6 no.1
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• pp.111-119
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• 2011

Recently, urban redevelopment programs and expansion of social infrastructure have caused massive amounts of construction waste in construction fields, and the mounds of it keep increasing every year. The disposal of construction waste is emerging as a national and social issue and the recycled powder generated by the treatment process of waste concrete is all being abolished or buried. Therefore, the purpose of this study is to utilize waste sludge generated by the wet-type treatment process of waste concrete as materials(binder, filler) for cement composite. This study evaluates physical and mechanical properties of mortar using recycled powder according to heating temperature, contents and applications. As a result of the chemical analysis, recycled powder is composed mainly of CaO and $SiO_2$, and that it is even lower in the content of CaO than OPC. The charateristics of mortar using recycled powder, according to drying and heating temperature, shows that as the heating temperature increases, flow decreases. Also, compressive strength and porosity of mortar using recycled powder was superior when heating temperature was $600^{\circ}C$. Thus, it is revealed that an effective development of recycled powder is possible since the binder by cement composite recovers a hydraulic property during heating at $600^{\circ}C$.