• Journal of the Korea Institute of Building Construction
• /
• v.17 no.2
• /
• pp.175-181
• /
• 2017

The purpose of this study is evaluating the characteristics of tensile strength of UHPC and examining tensile performance of notched specimens by direct tensile test. For test variables, 120, 150, and 180MPa of target design standard strength were aimed at. With general water curing and $90^{\circ}C$ high temperature steam as curing conditions, the properties were reviewed. Overall, it was represented that the specimens of notch-type direct tensile strength concrete was effective in inducing central cracks compared with existing direct tension specimens. Through this, it was judged that data construction with high reliability was possible. Above all, in a graph of direct tensile strength and strain, in the case of steam curing at high temperature, there was great difference of initial tensile strength compared with water curing. As passing of ages, an aspect that the difference gradually decreased was shown. Maximum tensile strength was found to increase steadily with increasing age for all target design strengths in water curing, in the case of steam curing, the tendency to increase significantly due to the initial strength development effect at 7 days of age. The initial crack strength increases with age in case of underwater curing, in the case of steam curing, it was higher than that of water curing in 7 days, while the strength of 28 days was lowered. In this part, it is considered necessary to examine the arrangement condition of the steel fiber.

• Journal of the Korea Concrete Institute
• /
• v.19 no.6
• /
• pp.763-771
• /
• 2007

Over the last few decades, many researches have been conducted in order to find solution to the problem of corrosion in steel reinforced concrete. As a result, methods such as the use of stainless steel bars, epoxy coatings, and concrete additives, etc., have been tried. While effective in some situations, such remedies may still be unable to completely eliminate the problems of steel corrosion. Fiber reinforced polymer (FRP) elements are appealing as reinforcement due to some material properties such as high tensile strength, low density, and noncorrosive. However, due to the generally lower modulus of elasticity of FRP in comparison with the steel and the linear behavior of FRP, certain aspects of the structural behavior of RC members reinforced with FRP may be substantially different from similar elements reinforced with steel reinforcement. This paper presents the flexural behavior of one-way concrete slabs reinforced with FRP bars. They were simply supported and tested in the laboratory under static loading conditions to investigate their crack pattern and width, deflections, strains and mode of failure. The experimental results shows that behavior of the FRP reinforced slabs was bilinearly elastic until failure. Also, the results show that the FRP overreinforced concrete beams in this study can be safe for design in terms of deformability.

• Journal of Preventive Medicine and Public Health
• /
• v.2 no.1
• /
• pp.77-80
• /
• 1969

In the cities nowadays, the dwelling conditions of Cackroach are provided by use of various kinds of construction material, installation of heating and cooling facilities that maintain moderate temperature, filthy sanitation, and lack of knowledge about insect as mechanical Vector. Cakroach is infectious disease Vector, and it proves to be of much importance in the public health. Considering such importance, the author has surveyed the distribution of Cackroach in the housing areas of Seoul City from May 1969 to the end of August 1969, and has come to the following conclusion: 1. House dwelling Cackroach collected in the City of Seoul are of two species, i. e. Blatella Germanica Linneaus and Periplaneta Japonica Karny. 2. Most of cackroach collected in Seoul are Blatella Germanica Linneaus and they are distributed in whole area of Seoul while that of Periplaneta Japonica Karny is distributed only in the limited area. 3. Dwelling places of Blatella Germanica Lineaus are in grog shop, Korean food restaurants, bakery shops, and patient rooms in hospitals. Many of them are found in tile kitchens and dining rooms of restaurants, and tearooms. They live in groups at older houses with much crack, warm and humid places. 4. For method of collection, the hand collection was the most effective. In trap collection during the day time, when the trap is placed at the narrow corners off the ground after confirming the dwelling places of cackroach, the match trap was more effective than the flask trap in collecting. In case of collecting during the night time, the flask trap was much more effective method than the match trap.

• Journal of the Korea Institute of Building Construction
• /
• v.18 no.4
• /
• pp.337-345
• /
• 2018

In this study, observations of oil leakage samples taken from the actual site were performed to identify the causes of the oil leakage phenomenon. As a result, the separation of the material components was determined as the main cause of the oil leakage phenomenon based on the changes in the surface conditions, and verification of this was conducted. The evaluation results confirmed that the filler component of the asphalt mastic subsided with the lapse of the settling time, and that the difference ratio of the filler contents of the upper and lower specimens was up to 23.8% after day 28. Based on these results, a hypothesis on the oil leakage mechanism of asphalt mastic was established, and then modeling of the entire process of oil leakage was performed.

• Membrane Journal
• /
• v.17 no.3
• /
• pp.254-268
• /
• 2007

Sodium type faujasite(FAU) zeolite layers with diverse materials characteristics(Si/Al ratio, thickness, and structural discontinuity) were hydrothermally grown on a porous $\alpha-Al_2O_3$ tube, and then the $CO_2/N_2$ separation was evaluated at $30^{\circ}C$ for an equimolar mixture of $CO_2$ and $N_2$. Among hydrothermal conditions, $SiO_2$ content in hydrothermal solution seriously affected materials characteristics: with an increment in the $SiO_2$ content, Si/Al ratio, thickness, and structural discontinuity of grown FAU zeolite layer simultaneously increased. The present study reveals that structural discontinuity(intercrystalline voids due to an incomplete densification and cracks induced by GIS Na-P1 phase) is the most important variable affecting the $CO_2/N_2$ separation. Also, it was suggested that the $CO_2$ desorption in permeate side be the rate-determining(slowest) step in the overall $CO_2$ permeation.

• Membrane Journal
• /
• v.17 no.3
• /
• pp.174-183
• /
• 2007

The manufacturing process of metal membrane made of only metal mesh and both metal mesh and powder with using rolling process have been studied. In the rolling of metal mesh, selected metal meshes were rolled with the reduction ratio of 10%, 20%, and 30%, respectively. Such rolling process resulted in the decrease of mesh pore size through reduction the cross sectional area of mesh and changing the diameter of mesh wires. Also, it enhanced the filtration ratio of rolled mesh which is almost same as the filtration ratio of upper grade unrolled mesh and the reliability of membrane by making pore size distribution become more uniform. In fabricating metal powder layer onto metal mesh, using PVA(polyvinyl alcohol) as a binder of powder, drying the metal powder layer at $100^{\circ}C$ for 1 hr, and sintering it at $1,000^{\circ}C$ for 3 hr in vacuum were to be optimum conditions for obtaining good quality of metal powder layer on metal mesh with high pore density but no crack. With additional rolling of metal powder layer on metal mesh with 30% reduction before sintering, metal membrane which filtration ratio is about $0.7{\mu}m$ has been successfully manufactured.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.36 no.11
• /
• pp.1381-1389
• /
• 2012

The object of this study considers corrosion fatigue improvement of 7075-T6 aluminum by using shot peening treatment on 3.5% NaCl solution at room temperature. Aluminum alloy is generally used in aerospace structural components because of the light weight and high strength characteristics. Many studies have shown that an aluminum alloy can be approximately 50% lighter than other materials. Mostly, corrosion leads to earlier fatigue crack propagation under tensile conditions and severely reduces the life of structures. Therefore, the technique to improve material resistance to corrosion fatigue is required. Shot peening technology is widely used to improve fatigue life and other mechanical properties by induced compressive residual stress. Even the roughness of treated surface causes pitting corrosion, the compressive residual stress, which is induced under the surface layer of material by shot peening, suppresses the corrosion and increases the corrosion resistance. The experimental results for shot peened specimens were compared with previous work for non treated aluminum alloy. The results show that the shot peening treatment affects the corrosion fatigue improvement of aluminum alloys and the induced compressive residual stress by shot peening treatment improves the resistance to corrosion fatigue.

• Resources Recycling
• /
• v.20 no.6
• /
• pp.50-55
• /
• 2011

Using ultrasonic irradiation, the separation and recovery of PV cell, made of silicon wafer, from PV module was carried out through selective decomposition of EVA used as an interlaminated binder. The ultrasonic cleaner of bath-type (Output: 130 W, Frequency: 40 kHz) was used as an ultrasonic apparatus in this research. With the fixed distance of 2 cm, from ultrasonic generator to PV cell, the experiment of EVA decomposition was performed in various organic solvents such as Toluene, Trichloroethylene, O-dichlorobenzene, Benzene. And also their concentrations and temperature was changed to survey the optimum conditions. However EVA can be decomposed perfectly at $55^{\circ}C$ within 160 min in 5 M of all kinds of solvent, PV cell may be recovered with being damaged or broken severely. This damage may be resulted from the swelling of EVA in the process of decomposition. Whereas, at the condition of 5 M at $65^{\circ}C$, PV cell can be recovered with the state of minor damage or crack. This implies that the decomposition rate of EVA increases with an increase of temperature, thereby EVA can be decomposed before the swelling of EVA layer. Conclusively, it is possible for PV cell to be recovered within 40 min, at $65^{\circ}C$ in 5 M, with less damage.

• Journal of the Korea Concrete Institute
• /
• v.14 no.2
• /
• pp.216-222
• /
• 2002

With deterioration of the nation's infrastructure comes the growing, need for effective means of rehabilitating structures. Possibly one for the most challenging tasks is to upgrade the overall capacity of concrete structure. Therefore, considerable efforts are still being made to develop new construction materials. Rehabilitation of damaged RC structures occasionally requires the removal and replacement of concrete in the tension zone of the structural members. Typical situation where the tension zone repair is necessary is when the concrete in the tension zone in beams or slabs has spalled off as a result of corrosion in the bottom reinforcing bars or due to extensive fire. The rehabilitation of such conditions normally involves the removal of the concrete beyond the reinforcement bars, cleaning or replacing the tensile bars and reinstatement of concrete to cover the steel bars the original shape and size. This study focused on the flexural behavior of reinforced concrete beams strengthened by steel strand and carbon fiber sheet in the tension zone. The properties of beams are 15$\times$25 cm rectangular and over a 200cm span. Test parameters in this experimental study were strengthening methods, jacking volume, the number of sheet. We investigated the flexural behavior of simply supported RC beams which are strengthened with the carbon fiber sheet, monotonic loads. Attention is concentrated upon overall bending capacity, deflection, ductility index, failure mode and crack development of repaired and rehabilitated beams.

• Journal of the Korea Concrete Institute
• /
• v.19 no.4
• /
• pp.393-399
• /
• 2007

Concrete bridge decks are directly exposed to the severe environmental conditions such as rain water and deicing chemicals resulting in the freeze-thaw action and the rebar corrosion during their service lift. These deteriorations of bridge decks shorten the service lift and consequently they are the major concerns of the maintenance. The high performance concrete (HPC) deck is proposed as the alternative to minimize the deterioration problems. To develop more durable concrete deck, the performance characteristic tests of HPC mixtures were carried out. In this study, 4 different concrete mixtures were used varying the mineral admixtures as the cement replacement; ordinary portland cement (OPC), 20% fly ash (FA),20% fly ash with 4% silica fume (FS), and 40% ground granulated blast-furnace slag (BS). The design compressive strengths of HPC specimens were 27 MPa and 35 MPa, respectively. The results showed that the compressive strength of concrete did not much affect the durability of concrete. HPC with fly ash and silica lune (FS) were turned out to have the good durability and crack resistance.