• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.641-646
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• 2001

In early-age concrete, volumetric deformations due to thermal expansion and moisture transfer are restrained by various boundary conditions, and then restraint stresses occur in proportion to developed stiffness. With increase of the age, these stresses are gradually relieved by significant relaxation behavior of early-age concrete. Therefore, it is necessary to consider the stress relaxation in order to analyze the behavior of early-age concrete more accurately. In this paper, we propose a unified algorithm which combines a relaxation model with hydration model, heat conduction model, micropore structure formation model, moisture diffusion model and mechanical properties development model and develop a finite element program based on the algorithm. The program is applied to evaluate stress development if a temperature-stress test machine (TSTM) specimen and a massive concrete structure, and then validity of the program is discussed and evaluated.

• Proceedings of the KSR Conference
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• 2008.11b
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• pp.1065-1068
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• 2008

Concrete is still one most common construction materials even in railway structures. As structures become massive and mega-sized, the importance of early age concrete quality control becomes more significant. Among various factors, relative humidity and temperature are the primary factors governing the early age quality. Temperature raise due to cement hydration causes stress, which can develop to cracking with internal and/or external restraints. Exposure conditions including ambient temperature, humidity and wind also significantly affect the cracking behavior of early age concrete. Among many of studies on the early age concrete behavior, investigation on the variation of temperature and relative humidity internal of concrete is not common. That is in part because the difficulties in measuring the relative humidity and temperature inside the concrete. This study used a digital sensor with an appropriate logger to measure internal temperature and relative humidity. This direct measuring method is expected to provide more reliable and comprehensive data acquisition on the early age behavior of concrete.

• Journal of Korean Biological Nursing Science
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• v.2 no.2
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• pp.20-37
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• 2000

The purpose of this study was to investigate the relationships between the differentials in life styles and their effect on the epidermal facial tissue in order to provide a basis for health professionals so that they might better be able to maintain and promote healthy skin care and further delay the premature ageing of the epidermal facial tissue. The subjects consisted of 145 females of various ages who visited skin care room in cerming health promoting behaviors(Park In sook's Profile) and questions on their behavioral practices pertaining to personal skin care were used. The investigation also ess of the four parts of the epidermal facial tissue studied. All data collected wee entered into the SAS program and analyzed for frequency, percentages, the utilized Pusan. The study dates ranged from May 1, 1998 to May 30, 1998. The methods used for this investigation were a questionnaire survey consisting of general objective questions. The questions con a "skin analyzer" to measured levels of moisturizing hydrated, facial oils, and roughnmean, t-test, ANOVA, and Pearson Correlation Coefficients. The results of this study were as follows ; 1. Epidermal facial oil was at its highest levels in the chin area with additional decreasing levels in the forehead and nose regions. The least regions were those of the cheeks. The highest levels of hydration on the other hand started with the forehead followed by the area of the chin, the cheeks and the lowest level of epidermal facial hydration was in the region of the nose. 2. The average score of the performance in the health promoting behaviors variable was 139.51. The variables with the highest degree of the performance were rest and sleeping(35.71). The lowest degree was hiegenic life(23.44). 3. The relationship health promoting behaviors and epidermal condition was not correlated with oil, hydration and roughness of the skin surface. 4. Skin care behavioral characteristics related to epidermal condition were washing style and temperature of washing water. 5. General characteristics related to epidermal condition were occupation, education level, acne and melasma. In conclusion, this study showed that several factors were significant in the behavior of skin care. Clear knowledge of both internal and external factors which affect the epidermal condition will help women to pursue active and appropriate practices in their health behaviors and skin care.

• Proceedings of the Korea Concrete Institute Conference
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• 1994.10a
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• pp.83-86
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• 1994

High strength concrete increasingly used in various countries. Recently, great attetion is also paid to the high strength concrete in this country. To promote the actual application of high strength concrete, several series of high strength concrete have been made and applied to actual structures. The mechanical properties and the temperature rise due to generation of hydration heat have been also studied. The present study provides a firm base for the actual application of high strength concrete in the field.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.05b
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• pp.429-432
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• 2006

The shrinkage mechanism of high strength concrete is different from that of normal concrete. The shrinkage of normal concrete is subjected to evaporate moisture in concrete, but most shrinkage in high strength concrete is caused by chemical reaction. To analyze shrinkage of concrete exactly, it is necessary to divide drying shrinkage with autogenous shrinkage in terms of degree of hydration, especially in concrete with low W/C ratio. The proposed method can provide a rational basis for prediction of shrinkage in high strength concrete structure.

• Journal of the Korean Ceramic Society
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• v.34 no.5
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• pp.449-452
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• 1997

Quick hardened property and compressive strength experimented to the C4A3 quantities. Workability experimented to the hydration behavior as retarder added to the C4A3. Compressive strength reached {{{{ delta }}3h=300~350 kgf/$\textrm{cm}^2$, {{{{ delta }}6h=400~450 kgf/$\textrm{cm}^2$, {{{{ delta }}24h=500~550 kgf/$\textrm{cm}^2$. Flow loss rate reached 70.1% to retarder addition 0.12% after 15 min. Test items were SEM, XRD, TG-DTA, MCC, porosity and zeta potential.

• Proceedings of the Korea Concrete Institute Conference
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• 2010.05a
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• pp.475-476
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• 2010

Hydration products formed on the steel surface may impose the resistance to corrosion of steel when a concrete is exposed to a salt environment. In the present study, ordinary Portland cement (OPC), calcium aluminate cement (CAC) and calcium hydroxide are applied as coating materials on the steel surface to consider the hydrations of each binder at corrosion. Corrosion is measured in terms of the corrosion potential and galvanic current to detect the effects in mitigating the corrosion behavior.

• Geomechanics and Engineering
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• v.13 no.3
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• pp.459-474
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• 2017

To investigate the mechanical properties of Expanded Polystyrene (EPS) Beads Stabilized Lightweight Soil (EBSLS), Laboratory studies were conducted. Totally 20 sets of specimens according to the complete test design were prepared and tested with unconfined compressive test and consolidated drained triaxial test. Results showed that dry density of EBSLS ($0.67-1.62g/cm^3$) decreases dramatically with the increase of EPS beads volumetric content, while increase slightly with the increase of cement content. Unconfined compressive strength (10-2580 kPa) increases dramatically in parabolic relationship with the increase of cement content, while decreases with the increase of EPS beads volumetric content in hyperbolic relationship. Cohesion (31.1-257.5 kPa) increases with the increase of cement content because it is mainly caused by the bonding function of hydration products of cement. The more EPS beads volumetric content is, the less dramatically the increase is, which is a result of the cohesion between hydration products of cement and EPS beads is less than that between hydration products of cement and sand particles. Friction angle ($14.92-47.42^{\circ}$) decreases with the increase of EPS beads volumetric content, which is caused by the smoother surfaces of EPS beads than sand grains. The stress strain curves of EBSLS tend to be more softening with the increase of EPS beads content or the decrease of cement content. The shear contraction of EBSLS increases with the increase of $c_e$ or the decrease of $c_c$. The results provided quantitative relationships between physico-mechanical properties of EBSLS and material proportion, and design process for engineering application of EBSLS.

• Advances in concrete construction
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• v.9 no.3
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• pp.279-287
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• 2020

This paper focuses on the engineering properties of Bentonite-Cement-Sodium silicate (BCS) grout, which was prepared by partially replacing the ordinary Portland cement in Cement-Sodium silicate grout with lithium bentonite (Li-bent) and sodium bentonite (Na-bent), respectively. The effect of different Water-to-Solid ratio (W/S) and various replacement percentages of bentonite on the apparent viscosity, bleeding, setting time, and early compressive strength of BCS grout were investigated. The XRD method was used to detect its hydration products. The results showed that both bentonites played a positive role in the stability of BCS grout, increased its apparent viscosity. Na-bent prolonged the setting time of BCS, while 5% of Li-bent shortened the setting time of BCS. The XRD analysis indicated that the hydration products between the mixture containing Na-bent and Li-bent did not differ much. Using bentonite as supplementary cementitious material (SCM) to replace partial cement is a promising way to cut down on carbon dioxide emissions and to produce low-cost, eco-friendly, non-toxic, and water-resistant grout. In addition, Li-bent was superior to Na-bent in improving the strength and the thickening of BCS grouts.

• Phonetics and Speech Sciences
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• v.5 no.4
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• pp.53-61
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• 2013

Voice disorders are most common in female teachers due to work-related vocal demands; however, only a few studies tried to evaluate individual risk factors with work-related risk factors to diagnose voice disorders. This study evaluated sixty-seven female elementary teachers (36 with voice disorders and 31 without voice disorders) to compare their vocal misuse, overuse, and vocal hygiene behaviors. Total Voice Handicap Index scores and VHI subscale (P, E, F) scores were not significantly different between two groups (p>0.05) and there was no relationship between VHI and acoustic measures (p>0.05). Loud talking, talking in noisy situations, and excessive speaking were significantly more frequent in female teachers with voice disorders (p<0.05) and thereby these overuse and misuse behavioral patterns were identified as risk factors to develop voice disorders in female teachers. Also, hydration was the most common behavior for vocal hygiene when experiencing vocal fatigue; however, hydration with hot green tea or coffee and throat clearing were often misused for vocal hygiene. This study found that female teachers from both groups presented higher voice handicap regardless of voice disorders. This study suggests a multidimensional voice assessment protocol is required to reflect voice problems in teachers and a vocal education program may be important to improve vocal hygiene knowledge and behavioral changes in female teachers.