• Journal of the Korea Concrete Institute
• /
• v.25 no.3
• /
• pp.347-354
• /
• 2013

Recently, crushed fine aggregates are being widely used due to the shortage of natural sand. In Korea, the amount of fine particles under 0.08 mm contained in crushed fine aggregates is restricted to be less than 7%, which is similar to the regulations of ASTM but is still very strict compared to the regulations of the other nations. In addition, the crushed aggregates already have in them about 20% of fine particles under 0.08 mm which occurs while they are crushed. The fine particles are not easy to wash out, and also to maximize the use of resources it is deemed necessary to review the possibility of enhancing the limit of the amount of fine particles. Therefore, this study conducted experiments to analyze the characteristics of fine particles under 0.08mm and their influence on the properties of concrete. Experiments using silt and cohesive soil were also done for comparison. In the experiments on fine particles, the methylene blue value was more in the soil dust contained in silt and cohesive soil than in the stone powder contained in crushed fine aggregates. Also, the methylene blue value had a close correlation with packing density and liquid & plastic limit. In the experiments done with concrete, the quantity of high range water reducing agent demanded to obtain the same slump increased as the fine particle substitution rate heightened. However, in the experiment which used stone powder testing the compressive strength and tensile strength of concrete in the same water-cement ratio, there was little change in strength with less than 20% addition of fine particles among the fine aggregates, and no meaningful difference in the amount of drying shrinkage of concrete.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.14 no.6
• /
• pp.1417-1425
• /
• 1990

In this paper, when the glass plate of fragile material is subjected to impact load, the fracture pattern and the generation phenomenon of cone crack were theoretically clarified by using the analysis method of impulsive stress in the first paper. The numerical analysis results of strain distribution at a distance of 0.1cm, from the impact loading point to 5cm, were compared with experimental results. The main conclusions obtained are as follows; (1) The generation phenomenon of cone crack at the impact fracture of the glass plate can be analytically confirmed by using the three dimensional dynamic theory of elasticity. And the numerical analysis results of strain distribution using this theory are relatively in close agreement with the crack size obtained from the impact fracture experiment. (2) After the stress wave generated at the impact point propagated to the spherical compressive wave, this stress wave reflected from the back surface and reached again at the surface of the plate to the spherical stress wave. Then the generation of cone crack can be confirmed along the stress wave surface. (3) The plate is the thicker, the more is the generation phenomenon of cone crack at the lower impact velocity range (20m/s-35m/s). Because the fracture generate before the maximum tensile stress acting to the glass plate, cone crack was rarely ever generated.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.22 no.5
• /
• pp.463-474
• /
• 2009

Double symmetric patch repair of existing structures always causes membrane action only, however, in many cases this technique is not practical. On the other hand, the bending stiffness of the patch and the skin increases as tensile loading is increased and affects the bending deformation significantly in the case of single-sided patch repair. In this study, the p-convergent full layerwise model has been proposed to determine the stress concentration factor in the vicinity of a circular hole as well as across the thickness of plates with single-sided patch repair. In assumed displacement field, the strain-displacement relations and 3-D constitutive equations of a layer are obtained by the combination of 2-D and 3-D hierarchical shape functions. The transfinite mapping technique has been used to represent a circular boundary and Gauss-Lobatto numerical integration is implemented in order to directly obtain stresses occurred at the nodal points of each layer without other extrapolation techniques. The accuracy and simplicity of the present model are verified with comparison of the previous results in literatures using experiment and conventional 3-D finite element. Also, the bending effect has been investigated with various patch types like square, circular and annular shape.

• KOREAN JOURNAL OF PACKAGING SCIENCE & TECHNOLOGY
• /
• v.5 no.1
• /
• pp.6-12
• /
• 1999

This study was conducted to investigate the application of edible films to Raymyun soup packaging. The sorption isotherm curve and BET monolayer moisture content of Raymyun soup were estimated as a basic experiment. Also, the mechanical properties, water vapor permeability, and solubility of the films were investigated. Methylcellulose, sodium caseinate, and K-carrageenan films were used as edible films and glycerol and polyethylene glycol(MW 400) were used as plasticizers. In case tensile strength, methylcellulose films was 68.56 MPa and sodium caseinate film was 7.11 MPa. The elongations of sodium caseinate, methylcellulose, and K-carrageenan film were 115.41%, 23.79% and 0.60%, respectively. The water vapor permeabilties values of methylcellulose, sodium caseinate, and K-carrageenan film between 50% and 70% RH were $0.25-0.38ng{\cdot}m/m^2{\cdot}sec{\cdot}Pa,\;0.62-0.84ng{\cdot}m/m^2{\cdot}sec{\cdot}Pa\;and\;0.31-0.55ng{\cdot}m/m^2{\cdot}sec{\cdot}Pa$, respectively. For the solubility of films, sodium caseinate film showed the highest solubility and methylcellulose film showed the lowest solubility.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.22 no.2
• /
• pp.155-169
• /
• 2002

The objective of this study was to investigate the effect of crack opening and closure in the AE activities during fatigue test. Laboratory experiment using various materials and test conditions were carried out to identify AE characteristics of fatigue crack propagation. Compact tension specimens of 2024-T4 and 6061-T6 aluminum alloy were prepared for fatigue test. AE activities were analyzed based on the phase of the loading cycle. Generally, most of AE were generated when the crack begins' opening and the crack closes fully, whereas a few in the pull opening of the crack. Also AE activity in the peak loading of cycle was different with each specimen. However, in the same material, AE activity was not affected by the change of cyclic frequency (0.1, 0.2, 1.0Hz). It was found that AE activities during crack opening and closure depend on material properties such as micro-structure, tensile strength and yield strength.

• Journal of the Korea Concrete Institute
• /
• v.27 no.6
• /
• pp.677-685
• /
• 2015

In a will to subdue the brittleness as well as the low tensile and flexural strengths of ordinary concrete, researches are being actively watched worldwide on steel fiber-reinforced Ultra High Performance Concrete (UHPC) obtained by admixing steel fibers in ultra high strength concrete. For the purpose of maximizing advantage of UHPC, this study removes the upper flange of the steel girder to apply an inverted T-shape girder for the formation of the composite beam. This paper intends to evaluate the behavior of the shear connectors and the flexural characteristics of the composite beam made of the inverted T-shape girder and UHPC slab using 16 specimens considering the compressive strength of concrete, the mixing ratio of steel fiber, the spacing of shear connectors and the thickness of the slab as variables. In view of the test results, it seemed that the appropriate stud spacing should range between 100 mm and 2 or 4 times the thickness of the slab. Moreover, the relative displacement observed in the specimens showed that ductile behavior was secured to a certain extent with reference to the criteria for ductile behavior suggested in Eurocode-4. The specimens with large stud spacing exhibited larger values than given by the design formula and revealed that the shear connectors developed larger ultimate strength than predicted owing to the action of UHPC and steel after non-composite behavior. Besides, the specimens with narrow stud spacing failed suddenly through compression at the upper chord of UHPC before reaching the full capacity of the shear connectors.

• Conservation Science in Museum
• /
• v.16
• /
• pp.96-113
• /
• 2015

High-barrier films are used to store cultural heritage objects in a safe environment sealed from oxygen and moisture. One of the high-barrier films use populary E manufactured by Japanese company M from the 1990's. However, this product has stayed in wide use, due to dearth of research on related subjects - including studies comparing it with other similar products-, in spite of the fact that high price information about its characteristics and environmental conditions is largely lacking. This study examines the characteristics of a number of high-barrier films with the goal to establish environmental standards for safer conservation of cultural heritage objects. E by the Japanese manufacturer M is compared with four other films; an electronics packaging films by a Korean firm, a film specially produced for the purposes of experiment in this study and a zipper bag-type film. Experiments were performed to compare the properties and gas blocking ability of the films by looking at their cross-section and measuring the thickness, tensile strength, elongation, absorbance of UV and visible light, yellowing and the permeability for oxygen and vapor. Based on these experiments, there are observed changes under different environmental conditions and depending on the length of use through temparature and humidification reproucing test. The results showed that while the high-barrier film by the Korean manufacturer was suitable for use as a packaging material for cultural heritage objects, the zipper bag-type film (P) was ill-adapted for this purpose. Based on the experiments reproducing the real-world environment, the length of useful life was also determined for each.

• Journal of the Korea Institute of Building Construction
• /
• v.10 no.5
• /
• pp.95-102
• /
• 2010

In recent years, the demand for the development of high quality and cost effective materials, as well as the competition to ensure a diverse and sufficient amount of ready-mixed concrete, has been increasing rapidly. In this experiment, concretes made with different admixtures are blended with each other in different combinations and ratios, in order to identify potential problems. The first test was a slump level test, in which all of the concretes met the required numbers, as they also did in the test for air content. Plain organic acid concrete scored the highest in bleeding amount, but organic acid mix in general showed a similar outcome. In the early measurement of compressive strength, plain naphthalene concrete was the strongest. Of the blends, the 5:5 mix of organic acid and naphthalene was the strongest. In the standard measurement, the 5:5 mix of naphthalene and lignin was the strongest. Tensile strength tests revealed similar results. Length change rate proved to be greater in blended concrete than in plain concrete, and dry shrinkage rate was highest in the 7:3 ratio blends. Through SEM photo analysis, it was confirmed that the 7:3 ratio blends contained more micro-voids. In conclusion, with the exception of a specific few combinations, it was found that the blending of different types of concrete is undesirable due to the delayed coagulation time as well as the early decrease in strength.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.31 no.6C
• /
• pp.251-258
• /
• 2011

Steel pipe piles have been used as various deep foundation materials for a long time. Recent increase in steel material cost has made engineers reluctant in using it even with its good quality and ease of construction. Therefore when constructing with steel pipe pile, the decision to reuse the excessive pile length that is cut off from the designed pile head elevation after pile driving can be cost saving. This has caused many constructors to reuse the pile leftovers with new piles, but the absence of quantitative structural capacity behaviors of steel pipe pile after pile driving or appropriate countermeasures and standards in reusing steel pipe pile has resulted in wrong applications, pile structural integrity problems, inappropriate limitation of reusable pile length, etc. The structural performance analysis between a new pile and a pile that has undergone working state and ultimate state stress level during pile driving was performed in this research by means of comparing the results between the dynamic pile load test, tensile load test, charpy energy test and fatigue test for high strength steel of $440N/mm^2$ yield strength. Test results show that under working load conditions the yield strength variation is less than 2% and for ultimate load conditions the variation is less than 5% for maximum total blow count of 3000. The results have been statistically analyzed to check the sensitivity of each factors involved. From the test results, reusability of steel pipe pile lies not in the main pipe yield strength deviation but in the reduction of absorb energy, strength changes and quality control at the welded section, shape deformation and local buckling during pile driving.

• Journal of Conservation Science
• /
• v.36 no.5
• /
• pp.306-314
• /
• 2020

The use of synthetic resins in ceramic restoration poses several challenges, including aging and potential damage to artifacts, which has raised the need to investigate new materials and restoration methods. This study set out to incorporate full color 3D printing into the 3D digital technology-based restoration method, an emerging approach currently being researched, and to print out missing parts with color information. After examining material physical properties with an experiment, the investigator printed out missing parts from a white porcelain vessel and grayish-blue-powdered celadon plate and compared them in chromaticity and brilliance. The experimental results show that the outputs had comparable tensile strength to the original restoration materials, whereas the recorded compressive strength was approximately 1.4~2 times higher than that of the original restoration materials. According to the NIST table of color difference values, the white porcelain vessel was visible at ΔE^*ab 1.55, and the grayish-blue-powdered celadon plate was perceivable at 3.34. Even though it was impossible to express the colors accurately owing to printer limitations, this non-contact approach reduced the possibility of damage to the minimum. In conclusion, it can be applied to objects with a high chance of damage or generate display effects through purposeful color differentiation in missing parts.