• Proceedings of the Korea Concrete Institute Conference
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• 2006.05b
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• pp.201-204
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• 2006

It should be noted that the critical chloride threshold level is not considered to be a unique value for all conditions. This value is dependent on concrete mix proportions, cement type and constituents, presence of admixtures, environmental factors, reinforcement surface conditions, and other factors. In this study, the accelerated corrosion test for reinforcing steel was conducted by electrochemical and cyclic wet and dry seawater method, respectively and during the test, corrosion monitoring by half-cell potential method was carried out to detect the time to initiation of corrosion for individual test specimen. For this purpose, lollypop and right hexahedron test specimens were made for 31%, 42%, and 50% of W/C, respectively, and then the accelerated corrosion test for reinforcing steel was executed. It was observed from the test that the time to initiation of corrosion was found to be different with the water-cement ratio and accelerated corrosion test method, respectively and the critical chloride threshold values were found to range from 0.91 to $1.47kg/m^3$.

• Journal of the Korean Data and Information Science Society
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• v.28 no.6
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• pp.1547-1555
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• 2017

This paper studies Bayesian test of homogeneity in contingency tables made by discretizing a continuous variable. Sometimes when we are considering events of interest in small area setup, we can think of discretization approaches about the continuous variable. If we properly discretize the continuous variable, we can find invisible relationships between areas (groups) and a continuous variable of interest. The proper discretization of the continuous variable can support the alternative hypothesis of the homogeneity test in contingency tables even if the null hypothesis was not rejected through k-sample tests involving one-way ANOVA. In other words, the proportions of variables with a particular level can vary from group to group by the discretization. If we discretize the the continuous variable, it can be treated as an analysis of the contingency table. In this case, the chi-squared test is the most commonly employed method. However, further discretization gives rise to more cells in the table. As a result, the count in the cells becomes smaller and the accuracy of the test becomes lower. To prevent this, we can consider the Bayesian approach and apply it to the setup of the homogeneity test.

• Computers and Concrete
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• v.21 no.3
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• pp.249-259
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• 2018

The use of recycled aggregate in concrete is gaining much attention due to the growing need for sustainability in construction. In the present study, Self Compacting Concrete (SCC) is made using both natural and recycled aggregate (crushed recycled concrete aggregate from building demolished waste) and performance of recycled aggregate based SCC for the bond behaviour of reinforcement is evaluated. The major factors that influence the bond like concrete compressive strength (Mix-A, B and C), diameter of bar ($D_b=10$, 12 and 16 mm) and embedment length of bar ($L_d=2.5Db$, $5D_b$ and full depth of specimen) are the parameters considered in the present study in addition to type of aggregates (natural and recycled aggregates). The mix proportions of Natural Aggregate SCC (NASCC) are arrived based on the specifications of IS 10262. The mix proportions also satisfy the guidelines of EFNARC. In case of Recycled Aggregate SCC (RASCC), both the natural coarse and fine aggregates are replaced 100% by volume with that of recycled aggregates. These mixes are also evaluated for fresh properties as per EFNARC. The hardened properties like compressive strength, split tensile strength and flexural strength are also determined. The pull-out test is conducted as per the specifications of IS 2770 (Part-1) for determining the bond strength of reinforcement. Bond stress versus slip curves were plotted and a typical comparison of RASCC is made with NASCC. The fracture energy i.e., area under the bond stress slip curve is determined. With the use of recycled aggregates, reduction in maximum bond stress is noticed whereas, the normalised maximum bond stress is higher in case of recycled aggregates. Based on the experimental results, regression analysis is conducted and an equation is proposed to predict the maximum bond stress of RASCC. The equation is in good agreement with the experimental results. The available models in the literature are made use to predict the maximum bond stress and compare the present results.

• Journal of the Korea Concrete Institute
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• v.19 no.6
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• pp.701-706
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• 2007

This study evaluated the durability of high-performance shotcrete mixed in the proper proportions using alkali-free and cement mineral accelerators as a permanent support that maintains its strength for the long term. Durability tests were performed the chloride permeability, repeated freezing and thawing, accelerated carbonation, and the effects of salt environments. Test results showed that all the shotcrete mixes included silica fume had low permeability. In addition, after 300 freeze/thaw cycles, the shotcrete mix had excellent freeze/thaw resistance more than the 85% relative dynamic modulus of elasticity. The accelerated carbonation test results were no effect of accelerator type but, the depth of carbonation was greater in the shotcrete mix containing silica fume. No damage was seen in a salt environments. Therefore, the high performance shotcrete mix proportions used in this study showed excellent durability.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.05b
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• pp.245-248
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• 2005

It should be noted that the critical chloride threshold level is not considered to be a unique value for all conditions. This value is dependent on concrete mixture proportions, cement type and constituents, presence of admixtures, environmental factors, steel reinforcement surface. conditions, and other factors. In this study, the accelerated corrosion test for reinforcing steel was conducted by electrochemical and cyclic wet and dry seawater method, respectively and during the test, corrosion monitoring by half cell potential method was carried out to estimate the chloride corrosion threshold value when corrosion for reinforcing steel in concrete was perceived. For this purpose, lollypop and right hexahedron test specimens were made for 31.4$\%$, 41.5$\%$ and 49.7$\%$ of w/c, respectively and then the accelerated corrosion test for reinforcing steel was executed. It was observed from the test that the time to initiation of corrosion was found to be different with water-cement ratio and accelerated corrosion test method, respectively and the chloride corrosion threshold value was found to range from 0.91 to 1.43 kg/$m^{3}$.

• Journal of Periodontal and Implant Science
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• v.29 no.2
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• pp.371-387
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• 1999

The present study was performed to assess and compare the clinical and microbiological effects following local application of 2% minocycline gel or 0.1% chlorhexidine subgingival irrigation to augment scaling and root planing in patients with moderate to advanced chronic adult periodontitis. 32 healthy patients with moderate to advanced chronic adult periodontitis were enrolled in the study. In each patient, the quadrants that had 2 or more teeth with $5{\sim}8mm$ probing pocket depth and radiographic evidence of alveolar bone loss were selected and divided into test side and control side according to the split-mouth design. All patients received standardized oral hygiene instructions at the beginning of the study and all remaining teeth received scaling and root planing until 0 week. The 2% minocycline gel was applied to periodontal pocket at 0, 1, 2, 3 week in the test side. The 0.1% chlorhexidine solution and the normal saline were irrigated subgingivally for about 30 seconds in the positive control side and negative control side respectively. The clinical and microbiological analysis carried out at 0, 4, 8, and 12 weeks . The results of this study were as follows; 1. In saline irrigation group, there was no adjunctive effects in probing pocket depth reduction, sulcular bleeding index and no significant changes in relative proportions of subgingival bacteria. 2. The chlorhexidine irrigation as an adjunct to scaling and root planing results in reduction in the plaque index and sulcular bleeding index, but there was not statistically significant. The relative proportion of spirochetes was significantly reduced, but the proportion of motile rods was no significant reduction. 3. The minocycline gel delivered subgingivally as an adjunct to scaling and root planing provide significant benefit in reducing probing depths and sulcular bleeding index compared to saline and chlorhexidine irrigation groups. 4. The relative proportions of spirochetes and motile rods were significantly reduced and the proportions of cocci and non-motile bacteria were correspondingly increased in the minocycline gel group. In conclusion, minocycline gel delivered subgingivally as an adjunct to scaling and root planing induces clinical and microbial responses more favorable for periodontal health than saline and chlorhexidine subgingival irrigation.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.3
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• pp.27-34
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• 2017

Recently, the importance of the industrial warehouse floor has been increasing due to the development of the distribution and logistics industry. In this present study, an early-hardening polymer floor mortar which can compensate for the limitation of conventional cement based floor mortar regarding fluidity and long curing time was developed. In order to achieve the early-hardening of mortar characteristic ultra rapid hardening cement was used as binder. Four types of mixture proportions in accordance with the vinyl acetate ethylene(VAE) polymer contents with range from 10% to 20% and the other proto proportion without VAE polymer were designed. Mechanical experiments including the fluidity test, compressive strength test, bending test, bond test, and abrasion test were conducted for all mixture proportions. From the flow test result, it was possible to achieve the high flow with 250 mm by controlling the amount of superplasticizer. The incorporation of VAE polymer was found to affect the compressive strength reduction, however, the flexural strength was higher than that of the proto mixture, and it was evaluated to increase the compressive strength / flexural strength ratio. Moreover, at least 2.6 times higher bond strength and more than 4 times higher abrasion resistance were secured. From the mechanical experiments results, the optimum mixing ratio of the VAE polymer was determined to be 10%. As a result of application and monitoring, it shows that it has excellent resistance to cracking, discoloration, impact, and scratch as well as bond performance compared to the cement based floor mortar.

• Journal of Korean Academy of Nursing
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• v.35 no.1
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• pp.186-194
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• 2005

Purpose: The purpose of this study was to investigate the effect of aromatherapy on pain, depression, and feelings of satisfaction in life of arthritis patients. Method: This study used a quasi-experimental design with a non-equivalent control group, pre-and post-test. The sample consisted of 40 patients, enrolled in the Rheumatics Center, Kangnam St. Mary's Hospital, South Korea. The essential oils used were lavender, marjoram, eucalyptus, rosemary, and peppermint blended in proportions of 2:1:2:1:1. They were mixed with a carrier oil composed of almond (45%), apricot(45%), and jojoba oil(10%) and they were diluted to 1.5% after blending. The data were analyzed using an 2-test, Fisher's exact test, t-test and paired t-test. Result: Aromatherapy significantly decreased both the pain score and the depression score of the experimental group compared with the control group. However, aromatherapy didn't increase the feeling of satisfaction in life of the experimental group compared with the control group. Conclusion: The result of this study clearly shows that aromatherapy has major effects on decreasing pain and depression levels. Based on our experiment's findings, we suggest that aromatherapy can be a useful nursing intervention for arthritis patients.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.519-522
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• 2005

As this study is to test effects of chemical attack on deterioration of cement mortars using in crushed sand. Besides tests have been carried out with cement mortars by river sand and crushed sand by fine sand, cement mortars mix various proportions of slica fume and fly ash(up to $15\%$ and $50\%$ by weight for cement) were prepared and immersed in pure water, sodium sulfate solution, magnesium sulfate solution, seawater for 28days. Test on the change in the weight and compressive strength of cement mortars according to the duration of immersion time and the content of slica fume and fly ash was performed.

• Geomechanics and Engineering
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• v.15 no.4
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• pp.957-964
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• 2018

In this study, a method of electrochemical consolidation is applied. This method utilizes electro-osmosis, which is an effective ground improvement technique for soft clays, and soil treatment using lime, which is the oldest traditional soil stabilizer. The mechanism of lime treatment for soil involves cation exchange, which leads to the flocculation and agglomeration. Five representative laboratory tests-an electro-osmotic test and four electrochemical tests with various proportions of lime-were performed on dredged marine clay. The objectives of this study are to investigate the effect of electrochemical treatment and to determine the optimum dose for optimal consolidation performance of dredged marine clay. The results show that a better consolidation effect was achieved in terms of current, temperature, and vane shear strength by using electrochemical treatment. The best results were observed for the electrochemical test using 4% lime content.