• Journal of the Korean Recycled Construction Resources Institute
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• v.6 no.1
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• pp.36-42
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• 2018

GGBFS(Ground Granulated Blast Furnace Slag)-replacement is very effective for improving resistance to chloride attack and this can induce a long service life for RC(Reinforced Concrete) structures exposed to chlorides. In the work, the design parameters such as cover depth, surface chloride content, critical chloride content, and replacement ratio of GGBFS are considered, and optimum replacement ratio of GGBFS are derived with intended service life. The changes of surface chloride content and cover depth show 3.16~3.38 and 3.02~3.34 times of service life variation, which are most influencing parameters. Critical chloride content shows 1.53~1.57 times of service life variation regardless of w/b(Water to Binder) ratios. In the case of surface chloride content $18.0kg/m^3$, the most severe condition, cover depth over 70 mm and GGBFS replacement ratio over 42% are required with concrete containing w/b ratio under 0.42 for 100 years of intended service life. The condition of $13.0kg/m^3$, GGBFS replacement over 35% is required. For reasonable durability design, quantitative exterior condition and critical chloride content should be determined, and the criteria in Domestic Specification is evaluated to be conservative.

• Journal of Aquaculture
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• v.9 no.4
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• pp.345-351
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• 1996

Mass production of resting egg of the rotifer, Brachionus plicatilis was carried out in 1 $m^3$ tank for L-type rotifer and in 1 $m^3$ and 4 $m^3$ tank for S-type rotifer. L-type rotifer was fed on concentrated Chlorella + baker's yeast and only baker's yeast for 15 days. S-type rotifer was fed on concentrated Chlorella in 1 $m^3$ tank for 7 days and frozen Chlorella + baker's yeast in 4 $m^3$ for $6\~8$ days. Total number of resting egg and number of resting egg from $10^8$ rotifers and 1 g dry weight diet for L-type rotifer fed on Chlorella + baker's yeast were $54.5{\times}10^6$ eggs, $30.5{\times}10^6$ eggs and $100{\times}10^3$ eggs, respectively. These were higher than those of rotifer fed on baker's yeast only. Total number of resting egg and number of resting egg from $10^8$ rotifers and 1 g dry weight diet for S-type rotifer fed on concentrated Chlorella in 1 $m^3$ tank were $50\~104{\times}10^6$ eggs, $47\~82{\times}10^6$ eggs and $136\~260{\times}10^3$ eggs, respectively. In 4 $m^3$ tank with frozen Chlorella + baker's yeast, these were $149\~567{\times}10^6$ eggs, $36\~123{\times}10^6$ eggs and $131\~338{\times}10^3$ eggs, respectively. This result suggests that S-type rotifer are better than L-type rotifer for the mass production of resting egg of the Korean rotifer.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.3
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• pp.276-285
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• 2020

In this study, accelerated chloride diffusion tests were performed on OPC(Ordinary Portland Cement) and FA(Fly Ash) concrete considering three levels o f W/B(Water to Binder) ratio o n 1,095 curing days. The accelerated chloride diffusion coefficient and the passed charge were evaluated in accordance with Tang's method and ASTM C 1202, and the resistance performance to chloride attack improved over time. FA concrete showed excellent resistance performance against chloride penetration with help of pozzolanic reaction. As the result of the passed charge, FA concrete showed durability improvement, "low" grade to "very low" grade, but OPC concrete changed "moderate" grade to "low" grade at 1,095 curing days. After assuming the design variables used for durability design as normal distribution functions, the service life of each case was evaluated by the probabilistic analysis method based on MCS(Monte Carlo Simulation). In FA concrete, the increase of probability of durability failure was lower than that of OPC concrete with increasing time, because the time-dependent coefficient of FA concrete was up to 3.2 times higher than OPC concrete. In addition, the service life by probabilistic analysis was evaluated lower than the service life by deterministic analysis, since the target probability of durability failure was set to 10%. It is considered that more economical durability design will be possible if the mo re suitable target probability of durability failure is set for various structures through researches on actual conditions and indoor tests under various circumstances.

• Journal of Aquaculture
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• v.18 no.2
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• pp.115-121
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• 2005

This study was performed to investigate the formation and mass production of resting eggs by freshwater rotifer, Brachionus calyciflorus as influenced by different aeration supplements and exchange intervals of culture water in 15-L culture vessels and 500 L culture tanks. The maximum densities and mixis rates of the rotifers were not different between experimental group exposed to air or oxygen supplements. However, the fertilization rate and formation of resting eggs of the rotifers in the air-supplemented group were significantly higher than those in the oxygen supplemented group. In the experiment concerning exchange interval of culture water, the maximum density of the rotifers and formation of resting eggs in the batch culture were significantly higher than those in the semi-continuous culture with exchange of water every day. The formation of resting eggs per Chlorella dry weight was highest in the semi-continuous culture with exchange of water every day. The resting eggs of rotifers were produced at a density of $51.8{\sim}57.9{\times}10^6$ eggs in 500-L culture tanks. In this study, the batch culture with air is an effective method for mass production of resting eggs by the freshwater rotifer, B. calyciflorus, and the efficiency of mass production of resting eggs by this rotifer was similar to that of the seawater rotifers, B. plicatilis and B. rotundiformis.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.3
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• pp.39-46
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• 2020

Carbonation is a deterioration which degrades structural and material performance by permitting CO₂ and corrosion of embedded steel. Service life evaluation through deterministic method is conventional, however the researches with probabilistic approach on service life considering loading and cold joint effect on carbonation have been performed very limitedly. In this study, probabilistic service life evaluation was carried out through MCS (Monte Carlo Simulation) which adopted random variables such as cover depth, CO₂ diffusion coefficient, exterior CO₂ concentration, and internal carbonatable materials. Probabilistic service life was derived by changing mean value and COV (Coefficient of variation) from 100 % to 300 % and 0.1 ~ 0.2, respectively. From the analysis, maximum reduction ratio (47.7%) and minimum reduction ratio (11.4%) of service life were obtained in cover depth and diffusion coefficient, respectively. In the loading conditions of 30~60% for compressive and tensile stress, GGBFS concrete was effective to reduce cold joint effect on carbonation. In the tensile condition, service life decreased linearly regardless of material types. Additionally service life rapidly decreased due to micro crack propagation in the all cases when 60% loading was considered in compressive condition.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.5
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• pp.15-23
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• 2021

In this paper, service life for RC(Reinforced Concrete) substructure subjective to carbonation was evaluated through deterministic and probabilistic method considering field investigation data and Design Code(KDS 14 20 40). Furthermore changes in service life with increasing COV(Coefficient of Variation) and equivalent safety index meeting the same service life were studied. From the investigation, the mean and its COV of cover depth were evaluated to 70.0 ~ 90.0 mm and 0.2, respectively. With intended failure probability of 10.0 % and 70 mm of cover depth, service life decreased to 137 years, 123 years, and 91 years with increasing COV of 0.05, 0.1, and 0.2, respectively. In the case of 80 mm of cover depth, it changes to 179 years, 161 years, and 120 years with increasing COV. The equivalent safety index meeting the same service life from deterministic method showed 1.66 ~ 3.43 for 70 mm of cover depth and 1.61 ~ 3.24 for 80 mm of cover depth, respectively. The various design parameters covering local environment and quality condition in deterministic method yields a considerable difference of service life, so that determination of design parameters are required for exposure conditions and parameter variation.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.6
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• pp.53-60
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• 2019

The purpose of this study is to evaluate the degree of improvement in strengths by mixing blast-furnace slag and fly ash in polymer cement mortar(PCM). The test specimens are prepared with EVA polymer dispersion, two types of Admixtures (blast-furnace slag and fly ash), five kinds of polymer-cement ratios (0, 5, 10, 15 and 20%), and six kinds of admixtures (0, 3, 5, 10, 15 and 20%). Plain cement mortar is also made for comparison. From the test results, the flowing of PCM is greatly improved with the mixing of the admixtures, and strengths of PCM compared to ordinary cement mortar are also improved due to a decrease in water cement ratio. In addition, the strength characteristics of PCM by admixtures are greatly improved in flexural strength with fly ash compared to other strengths. It is apparent that the optimum mix proportions with polymer-cement ratio of 10% or more, admixture contents 5 to 10% of flay ash for flexural strength improvement of EVA-cement mortar are recommended in this study.

• Journal of the Korean Recycled Construction Resources Institute
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• v.5 no.3
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• pp.239-246
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• 2017

RC(Reinforced Concrete) structures can keep their performance during intended service life through initial service life and extension of the life through repairs. In the deterministic repairing method, cost and the related $CO_2$ emission increase with step-shaped escalation, however continuous results can be obtained through probabilistic repairing technique, and this is capable of reducing $CO_2$ emission through $CO_2$ absorption. In the work, repairing timing and $CO_2$ emission/absorption are evaluated based on the different methods like deterministic and probabilistic manner. The probabilistic technique considering $CO_2$ absorption with carbonation progress is evaluated to be very effective to reduction of $CO_2$ emission through extension of initial and additional service life due to repairs. When the variations of the service life from initial construction and repair material can be determined, the proposed technique can contribute to reduction of cost and $CO_2$ with decreasing repairing number.

• KDI Journal of Economic Policy
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• v.27 no.2
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• pp.123-154
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• 2005

Using Korean household data, this paper examines how consumption of durable goods is determined. Previous studies report that the standard Permanent Income Hypothesis (PIH), while being broadly consistent with non-durable goods consumption, provides little explanation for durable goods consumption. In this paper, we consider the (S, s) model as an alternative to the standard PIH. The (S, s) model predicts that, because of fixed adjustment costs, consumers make no adjustment to the durable goods stock until deviation from the optimal level becomes large. When the adjustments are made, the durable goods stock attains the optimal level. In order to test this prediction, we examine the intra-temporal relationship between non-durable goods and durable goods consumption and intertemporal changes in durable goods consumption, using data from the Korean Household Panel Study. The results show that, while the standard PIH is rejected by the data, the (S, s) model is not.

• Journal of Aquaculture
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• v.9 no.4
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• pp.339-344
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• 1996

The effect of temperature ($24\~36^{\circ}C$ and salinities ($5\~30$ ppt) on hatching rate of the resting egg of the Korean rotifer, Brachionus plicatilis was investigated. The highest hatching rate of the resting egg was $85.7\%$ at $28^{\circ}C$ and 15 ppt. The hatching rates of the resting eggs with salinities were not significant at $326{\circ}C$ and $36^{\circ}C$. Hatching was faster at higher temperature. The resting eggs stored at $5^{\circ}C$ in dark hatched simultaneously within two days, however, those at $28^{\circ}C$ in dark hatched intermittently within 14 days. But, final hatching rate of the resting egg at $28^{\circ}C$ was higher at $28^{\circ}C$ than that at $5^{\circ}C$. With regard to drying temperature and time of resting egg, the resting egg dried at $30^{\circ}C$ for 1 hour showed the highest hatching rate ($46.4\%$).