• Journal of the Korean Recycled Construction Resources Institute
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• v.2 no.2
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• pp.128-136
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• 2014

It is known that the best way to recycle fly ash is to use in concrete. It is impossible to bury in the ground this fly ash recently, so it is trying to use high volume fly ash concrete. Nevertheless, recent main research topics are focused in the part of material only. However, it is necessary to perform the researches about elasticity modulus, stress-strain relationship and structural behavior. Therefore, in this paper, 18 test members were manufactured with 3 test variables, namely fly ash replacement ratio 0, 35, 50%, concrete compressive strength 20, 40, 60MPa and 2 tensile steel ratio. 18 test members were tested for flexural behavior. From the test results, there were no differences between 35, 50% high volume fly ash cement concrete and ordinary concrete without fly ash (FA=0%). In order to evaluate the HVFAC flexural behavior, Analytical model was proposed and the computer program was developed. There were no differences between test results and analysis results. So, the proposed analytical model was reasonable.

• Journal of Conservation Science
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• v.25 no.2
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• pp.179-196
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• 2009

The Gaetaesajiseokbulibsang (Treasure No. 219) consists of light gray and coarse to medium-grained granodiorite with feldspar phenocrysts in part. Magnetic susceptibility of the rock material was measured as 12.06(${\times}10^{-3}$ SI unit), being different from the granite($0.19{\times}10^{-3}$ SI unit) in the Mt. Cheonho. This indicates the raw material has been supplied from the outside. As a result of deterioration assessment, exfoliation of the Right Buddha, cement and dust of the Main Buddha were estimated as 35.2%, 21.1% and 25.0%. The ultrasonic velocity was measured as 2850.2m/s(Main Buddha), 2648.4m/s(Left Buddha) and 2644.5m/s(Right Buddha). The compressive strength calculated from the velocity showed low in the Right Buddha among three and the all pedestal parts which corresponds to the result of deterioration assessment. The indoor mean temperature and relative humidity of the shelter were $13.7^{\circ}C$ and 79.0%. It is evaluated that the indoor microclimate was stable and the shelter functioned to reduce climatic fluctuation of the outdoor. However, water condensation was occurred on the surface of the pedestal part during spring and summer, and freezing in winter season might also be done. These factors were probable to be a main cause of the surface exfoliation of the Triad Buddha Statues. Therefore, dehumidification and heating system in the shelter should be applied to prevent further deterioration.

• Journal of Korean Society of Environmental Engineers
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• v.36 no.2
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• pp.109-112
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• 2014

A porous ceramic which has fine porosity and small specific gravity is made with Cenosphere and Ball Clay under condition of $1,250^{\circ}C$ in calcination temperature and 30 minutes of calcination time. The average size of porous ceramic was about $2.5{\times}10^{-5}$ m and pores are well developed. The void-fraction of porous ceramic was 67.1% under the input of Cenosphere and Ball clay with the weight ratio of 100 to 5. However, as weight ratio of Ball Clay increased to 20, 40, 100, the void fraction decreased to 58.4, 56.7, 47% respectively. When the weight ratio of Cenosphere and Ball Clay was 100 to 100, the apparent density of porous ceramic was $1.04g/cm^3$. which is twice the density when the weight ratio of Ball Clay was 5. On the other hand, absorption rate decreased by at least 100%. In condition of weight ratio of Cenosphere and Ball Clay was 100 to 100, compressive strength of porous ceramic was 30 (MPa), improve by about 76% or more when the weight ratio of Ball Clay was 5.

• Journal of Korean Society of Disaster and Security
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• v.12 no.4
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• pp.43-52
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• 2019

To analyze the influence on the stability, resulting from application of upgrade pipe roof structure (UPRS) method to the structure existed under subway Station, physical properties of a ground, elasticity and elasto-plastic theories, including displacement analysis of finite elements, stress analysis of finite elements, displacement caused by steel pipe propulsion and internal excavation, and stress change in a steel pipe, were introduced. Then, the influence on structural stability when applying the UPRS method was compared and reviewed based on the construction management standard of the Ministry Land, Infrastructure and Transport and foreign sources, using numerical analysis with a model which assumes that each microelement divided into a structurally stable point consists of the connection of finite points. As a result of the finite element analysis, 7.21 mm maximum displacement, 1/3,950 angular displacement, 70.28 MPa bending compressive stress of steel pipe structure constructed with UPRS (non-excavation) method and 477.38 MPa maximum shear strength were within their allowable standards (25.00 mm, 1/500, 210.00 MPa and 120.00 MPa, respectively), and therefore, the results showed that the design and construction are stable.

• Journal of the Korea Organic Resources Recycling Association
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• v.25 no.2
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• pp.69-76
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• 2017

In the Korea, 80 percent of livestock manure were converted into compost and used as organic fertilizers. The livestock manure compost has two types of powder and pellet type (ID= 5~10 mm). The aim of this study was to investigate the properties of two types of cow manure compost pellet (cylinder and sphere type). Nitrogen concentrations of cylinder type and sphere type of compost pellets were 1.23 and 1.24%, respectively. There were similar with nitrogen concentration of cylinder and sphere types of compost pellets. As a result of analyzing the effect of granulation processing, it was found that the moisture content of the raw material was the most influential factor in the granulation processing in both of the processing types of the screw pressing method and the rotating cylinder method. When the cylinder and sphere types of compost pellets were dry to 20% of moisture content, the specific gravities of these compost pellets were 1.38 and 1.13, respectively. The compressive strength of cylinder type pellet and sphere type pellet were 27.6 and $11.3kg/cm^2$, respectively.

• The Journal of Engineering Geology
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• v.23 no.3
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• pp.235-246
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• 2013

P-wave velocity was measured by the low frequency flaw detector in order to analyze the weathered state of a halo stone Buddha, Unju temple, Hwasun, Korea. By the results of laboratory tests on a fresh acidic tuff with the same rock of a halo stone Buddha, average absorption, average P-wave velocity, and average uniaxial compressive strength were 5.38%, 4,008 m/s, and 70.1 MPa, respectively. The results correspond to moderately strong rock. Average P-wave velocity of a halo stone Buddha measured by the low frequency flaw detector was 2,257 m/s in the left zone, 3,437 m/s in the right zone, and 2,802 m/s overall. Weathering index of a halo stone Buddha was 0.45 in the left zone, 0.21 in the right zone, and 0.33 overall. Comparing the results of a halo stone Buddha with them of laboratory tests, weathered state of a halo stone Buddha was analyzed highly weathered state in the left zone and moderately weathered state in the right zone. Furthermore, it suggests that the left zone of a halo stone Buddha was affected weathering more than the right one. Overall a halo stone Buddha corresponds to moderately weathered state of weathering degrees. In conclusion, it is considered that low frequency flaw detector may be applicable as a valuable method on analyzing the P-wave velocity of the stone cultural heritage with an irregular surface.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.4
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• pp.371-377
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• 2014

In tissue engineering, a scaffold is a three-dimensional(3D) structure that serves as a template for regeneration the functions of damaged tissues or organs. Among materials for scaffolds, polycaprolactone(PCL) and ${\beta}$-tricalcium phosphate(${\beta}$-TCP) are biodegradable and biocompatible. In this study, we fabricated 3D PCL, blended PCL (60 wt %)/${\beta}$-TCP (40 wt %), and pure ${\beta}$-TCP scaffolds by a multi-head scaffold fabrication system. Scaffolds with a pore size of $600{\pm}20{\mu}m$ was observed by scanning electron microscopy. The effects of 3D PCL, blended PCL (60 wt %)/${\beta}$-TCP (40 wt %) and pure ${\beta}$-TCP scaffolds were analyzed by evaluating their mechanical characteristics. In addition, in an in-vitro study using osteoblast-like saos-2 cells, we confirmed the effects of 3D scaffolds on cellular behaviors such as cell adhesion and proliferation. In summary, the 3D blended PCL (60 wt %)/${\beta}$-TCP (40 wt %) scaffold was found to be suitable for human cancellous bone in terms of its the compressive strength, biocompatibility, and osteoconductivity. Thus, blending PCL and ${\beta}$-TCP could be a promising approach for fabricating 3D scaffolds for effective bone regeneration.

• Tunnel and Underground Space
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• v.18 no.5
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• pp.343-354
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• 2008

A new method is suggested herein to measure the virgin earth stresses by means of a borehole. This novel concept is basically a combination of borehole stress relieving and borehole fracturing techniques. The destressing of the borehole is achieved by means of inducing thermal tensile stresses at the borehole periphery by using a cryogenic fluid such as Liquid Nitrogen($LN_2$). The borehole wall eventually develops fractures when the induced thermal stresses exceed the existing compressive stresses at the borehole periphery in addition to the tensile strength of the rock. The above concept is theoretically analyzed for its potential applicability to interpret in situ stress levels from the tensile fracture stresses and the corresponding borehole wall temperatures. Coupled thermo-mechanical numerical simulations are also conducted using FLAC3D, with thermal option, to check the validity of the proposed techniques. From the preliminary theoretical and numerical analysis, the method suggested for the measurement of in situ stresses appears to be capable of accurate estimation of the virgin stresses by monitoring tensile crack formation at a borehole wall and recording the wall temperatures at the time of crack initiation.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.4
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• pp.766-771
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• 2016

This study examined the long-term durability of PC boxes, which was manufactured by low-carbon eco-friendly concrete using an alternative binder to cement and alternative fine aggregate to sand and microwave heat curing system to reduce the construction cost of a near-surface transit system. Based on the test results, the initial compressive strength of microwave heat cured concrete was higher than that of the steam cured concrete, but those were similar in the long-term age. In addition, there was no significant difference between the two curing conditions in the chemical resistance and the freeze-thawing resistance, and the chloride ion penetration level of the concrete cured by two methods was very low. Therefore, low-carbon eco-friendly concrete and microwave heat curing technology are expected to contribute to the economic construction of a near-surface transit system, and reduce carbon dioxide emissions and environmental impact.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.1
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• pp.208-215
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• 2018

The causes of column shrinkage and the codes that have been studied up to now are discussed. The documents mentioned in the code deal with the drying shrinkage, creep, compressive strength and elastic modulus of the specimen, and the elastic deformation calculated from the structural analysis. However, the deformation due to the temperature caused by the long term monitoring is less than that caused by the factors generated by the previous studies. In the previous studies, it was found that dehydration shrinkage, creep, and elastic deformation were not considered for temperature-induced deformation, while for the specimen experiments, the temperature-related items were replaced with the humidity-related terms The compensation value by the proposed equation showed error of 4.9 mm in the upper direction and 1.0mm in the lower direction when calculating column shortening, and it was found that its value by the proposed equation almost coincided with the measurement value in Site. Therefore, it is necessary to further study the temperature that can be omitted in calculating the existing column shortening, to consider the influence factors, and to supplement the criteria for the temperature measurement of the structure as well as the specimen tests.