• Proceedings of the Korean Institute of Building Construction Conference
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• 2021.05a
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• pp.195-196
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• 2021

The pore distribution of the cement mortar mixed with carbon nanotubes was found to have a large number of pores at (370~80)㎛, and the distribution ratio was larger as the carbon nanotubes were mixed. However, the pores with a fine particle diameter of (10-0.5) ㎛ were found to be larger as the carbon nanotubes were incorporated. However, the distribution of pores of the test specimens of conductive cement mortar with deterioration damage was found to be distributed in a number of particle diameters of (500 to 100) ㎛ and (10 to 0.5) ㎛. It is judged that the particle diameter of the internal pores increased due to the damage. However, as the mixing ratio of the test specimen with carbon nanotubes increased, the distribution of voids was relatively lower than that of plain, and it was judged to have excellent resistance to deterioration damage.

• Geomechanics and Engineering
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• v.15 no.5
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• pp.1113-1124
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• 2018

Geological dynamic hazards during deep coal mining are caused by the failure of a composite system consisting of the rock and coal layers, whereas the joint in coal affects the stability of the composite system. In this paper, the compression test simulations for the rock-coal combined body with single joint in coal were conducted using $PFC^{2D}$ software and especially the effects of joint length and joint angle on strength and failure characteristics in a rock-coal combined body were analyzed. The joint length and joint angle exhibit a deterioration effect on the strength and affect the failure modes. The deterioration effect of joint length of L on the strength can be neglected with a tiny variation at ${\alpha}$ of $0^{\circ}$ or $90^{\circ}$ between the loading direction and joint direction. While, the deterioration effect of L on strength are relatively large at ${\alpha}$ between $30^{\circ}$ and $60^{\circ}$. And the peak stress and peak strain decrease with the increase of L. Additionally, the deterioration effect of ${\alpha}$ on the strength becomes larger with the increase of L. With the increase of ${\alpha}$, the peak stress and peak strain first decrease and then increase, presenting "V-shaped" curves. And the peak stress and peak strain at ${\alpha}$ of $45^{\circ}$ are the smallest. Moreover, the failure mainly occurs within the coal and no apparent failure is observed for rock. At ${\alpha}$ between $30^{\circ}$ and $60^{\circ}$, the secondary shear cracks generated in or close to the joint tips, cause the structural instability failure of the combined body. Therefore, their failure models present as a shear failure along partial joint plane direction and partially cutting across the coal body or a shear failure along the joint plane direction. However, at ${\alpha}$ of $60^{\circ}$ and L of 10 mm, the "V-shaped" shear cracks cutting across the coal body cause its final failure. While crack nucleations at ${\alpha}$ of $0^{\circ}$ or $90^{\circ}$ are randomly distributed in the coal, the failure mode shows a V-shaped shear failure cutting across the coal body.

• Korean Journal of Heritage: History & Science
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• v.46 no.1
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• pp.176-187
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• 2013

A study has been carried out on metal materials in order to identify the quantitative relation between the concentration and damage characteristics after evaluation of the damage characteristics according to the $SO_2$ concentration. The prepared metal samples, which were categorized according to the material (silver, copper, iron, lead, brass) were exposed to 0.01, 0.12, 1, 10, 100, 1,000, and 5,000ppm of $SO_2$ for 24 hours and the optical, physical, chemical deterioration rates both before and after testing were evaluated. The results showed optical deterioration, a loss of gloss on silver specimen with $SO_2$ 100ppm, an increase of color difference on brass, iron, copper and lead specimens with $SO_2$ 5,000ppm, as well as physical changes such as an increase of thickness and corrosion rate on iron sample with $SO_2$ 5,000ppm. In the case of chemical changes such as an increase sulfate ion ($SO{_4}^{2-}$) concentration and decrease of pH on iron and brass specimens were identified. These results suggest that $SO_2$ 100ppm caused clear optical deterioration on some metals such as silver and physicochemical and optical deterioration were identified at $SO_2$ 5,000ppm regardless of metal type. Also, It was concluded that iron and brass are the most susceptible of the metal specimens to $SO_2$.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.14 no.5
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• pp.237-242
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• 2014

In this paper, we find out the lifetime index in order to determine the time-dependent trend of deteriorating performance of 6.6kV high-voltage power cable in operation at a power station. The cable systems used in our study have been in operation for 13 years. With measurements for the 13 years, we analyzed the insulation resistances. By developing measuring equipment (comprized mainly of transformer, temperature sensor, and LPF) operating by the three-phase electric power, we analyzed the changing characteristics of insulation resistance of power cable. In contrast to 22kV cables, 6.6 kV cables have thicker insulation. Therefore the characteristics of 6.6kV cables are different from that of 22kV cables. The study found that as time passes, the insulation resistance does not decrease continuously; it decreases to a certain value, then does not decrease any more and shows properties of oscillation. We could not detect the process of deterioration in the preceding twelve years. The cable system showed great stability so that deterioration was not apparent. In this case, it is not possible to measure the future life indices of power cables because the lifetime indices are not predictable

• Proceedings of the Korea Water Resources Association Conference
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• 2010.05a
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• pp.1710-1715
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• 2010

Service life of water pipes buried in the underground is considerably affected from various factors such as environmental characteristics, pipe characteristics, operation and maintenance, etc. Therefore it is difficult to determine their service life as uniformly the same value assigned by related laws and ordinances. As a result, the service life should be determined by the technical judgement based on the assessment for the condition of water pipes. In this study, It was established that the methodology could predict present and future failure risk, and plan short and long-term strategies for replacement/rehabilitation through the assessment for the physical deterioration and economical values of buried water pipe. The methodology was applied for the verification and reliability to several sites selected in multi-regional transmission pipelines. The proposed method could helps to support reasonable and economical decision of rehabilitation/replacement in the present and future. To improve conventional assessment method of aged water pipes, affecting factors are simplified based on the statistical analysis results from the measured data in the field and the physical deterioration mechanism for better reliability. Also, the guide-line is developed to carry out the reasonal rehabilitation planning through water pipe condition assessment.

• The Journal of Engineering Geology
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• v.23 no.4
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• pp.341-352
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• 2013

The physical and mechanical properties of red shale and black shale exposed in the Daegu area were investigated in tests conducted to determine unit weight, absorption ratio, porosity, ultrasonic velocity, unconfined compressive strength, point load strength, slake durability index, and deterioration characteristics. XRD, XRF, and SEM analyses were also performed on the shale specimens. While the unit weights of the two shales were similar, the absorption ratio and porosity were higher in the red shale than in the black shale. Despite the higher porosity of the red shale, the ultrasonic velocity, compressive strength, and point load strength were higher in the red shale, which is an unexpected result that may be due to the presence of fine laminations in the black shale. The deterioration rate, as determined from the point load strength and the slake durability index, increased with increasing immersion time and with the acidity of the immersion liquid. The deterioration rate was higher for the red shale than for the black shale because of the higher porosity of the former.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2008.06a
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• pp.355-356
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• 2008

• Journal of the Computational Structural Engineering Institute of Korea
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• v.28 no.3
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• pp.229-239
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• 2015

In light of the significant increase in the quantities of goods transported and the development of the shipping industry, the frequency of usage of port structures has increased; yet, the government's budget for the shipping & port of SOC has been reduced. Port structures require systematically effective maintenance and management trends that address their growing frequency of usage. In order to construct a productive maintenance system, it is essential to develop deterioration models of port structures that consider various characteristics, such as location, type, use, constructed level, and state of maintenance. Processes for developing such deterioration models include examining factors that cause the structures to deteriorate, collecting data on deteriorating structures, and deciding methods of estimation. The techniques used for developing the deterioration models are multiple regression analysis and Markov chain theory. Multiple regression analysis can reflect changes over time and Markov chain theory can apply status changes based on a probabilistic method. Along with these processes, the deterioration models of open-type and gravity-type wharfs were suggested.

• Journal of Conservation Science
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• v.28 no.4
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• pp.321-328
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• 2012

A $SO_2$ gas acceleration test was carried out on four textile groups (silk, cotton, ramie cloth, hemp cloth) which were categoried in five categories by the dyeing materials (undyed, red, yellow, blue, black) and the relation between the concentration of $SO_2$ and deterioration rate was evaluated. The textiles were exposed to 0.01, 0.12, 1, 10, 100, 1000, and 5000 ppm of $SO_2$ for 24 hours and the optical, physical, and chemical deterioration rates were studied. An optical change was identified as the color difference and grey scale rating (colorfastness) enhanced with the increase of gas concentration while there was little physical change. Chemical damage was caused by the acidification of the textile material due to the trapped sulfate ion concentration. The result of optical, physical, and chemical deterioration rates shows that 1 ppm/day $SO_2$ is a critical level of deterioration of traditional textiles.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.3395-3400
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• 2007

Heat transfer experiments at a vertical annulus passage were carried out in the SPHINX(Supercritical Pressure Heat Transfer Investigation for NeXt Generation) to investigate the heat transfer behaviors of supercritical $CO_2$. The collected test data are to be used for the reactor core design of the SCWR (SuperCritical Water-cooled Reactor). The mass flux was in the range of 400${\sim}$1200 kg/$m^2$s and the heat flux was chosen up to 150 kW/$m^2$. The selected pressures were 7.75 and 8.12 MPa. The heat transfer data were analyzed and compared with the previous tube test data. The test results showed that the heat transfer characteristics were similar to those of the tube in case of a normal heat transfer mode and degree of heat transfer deterioration became smaller than that in the tube. Comparison of the experimental heat transfer coefficients with the predicted ones by the existing correlations showed that there was not a distinct difference between the correlations.