• Proceedings of the Korea Concrete Institute Conference
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• 1999.04a
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• pp.697-702
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• 1999

Among several non-destructive testing methods, ultrasonic pulse velocity method has been widely used for the evaluation of concrete strength. However, this method might not provide accurate estimated results since factors influencing the relationship between strength and wave velocity is not considered. In this study, the evaluation methods of concrete strength using compression wave velocities measured by either ultrasonic pulse velocity method or impact-resonance method are proposed. A basic equation is obtained by the linear regression with velocity vs. strength data at a specific age and then, ageing factor is employed in the equation to consider the difference of the increasing rate between wave velocity and strength. Strengths predicted by the proposed equation agree well with test results.

• International Journal of Concrete Structures and Materials
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• v.7 no.2
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• pp.119-125
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• 2013

Carbonation is a natural ageing process for cement. This study focuses on how the carbonation rate varies with selected hydration times and atmospheric conditions during the early stages of reacting dried cement paste. Diffuse reflection Fourier transform infrared spectroscopy is shown to be a suitable technique to monitor the formation of carbonates in cement. Combined with a previously developed freeze drying technique, carbonation can be studied at specific hydration stages. In ambient air both calcium hydroxide and calcium silicate hydrate (C-S-H) in cement are carbonated. Increased hydration time enhances the carbon dioxide uptake, which indicates that the calcium in the hydration products reacts more easily than the calcium in the clinker phase. In a humid $CO_2$ atmosphere, the carbonation process is so pronounced that it decomposes C-S-H into calcium carbonate and silica. In a moist $N_2$ atmosphere no carbonation occurs, but the sulfate chemistry of the cement seems to be affected due to the formation of ettringite.

• Computers and Concrete
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• v.4 no.2
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• pp.101-117
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• 2007

A new model predicting the nonlinear basic creep behaviour of concrete structures subjected to high multi-axial stresses is proposed. It combines a model based on the thermodynamic framework of the elasto-plastic continuum damage theory for time-independent material behaviour and a rheological model describing phenomenologically the long-term delayed deformation. Strength increase due to ageing is regarded. The general 3D solution for the creep theory is derived from a rate-type form of the uniaxial formulation by the assumption of associated creep flow and a theorem of energy equivalence. The model is able to reproduce linear primary creep as well as secondary and tertiary creep stages under high compressive stresses. For concrete in tension a simple viscoelastic formulation is applied. The material law is then incorporated into a finite element solution procedure for analysis of reinforced concrete structures. Numerical examples of uniaxial creep tests and concrete members show excellent agreement with experimental results.

• Architectural research
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• v.16 no.4
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• pp.167-174
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• 2014

Smart Work is a way of working independent of time and space restrictions with the help of ICT. For past years, Korea has been promoting Smart Work to boost ICT industry, to overcome low birth rate and population ageing, and to implement Smart Korea. Three elements of Smart Work include people, technology and space. A lot of research has been performed on people and technology for Smart Work. But it is hard to find research on space. In this paper, some representative smart work centers(SWCs) in Korea were selected and analyzed from the perspective of spatial design including general characteristics, personal spaces, group spaces, and support spaces. From this research, it is observed that current SWCs in Korea are good in providing personal work spaces and simple group meeting rooms as well as ICT environments. However, they lack of openness to the public and group spaces to encourage informal communications. It is also observed that personal space plans need to be multi-functional, and that novel supporting spaces are required to improve quality of life and creativity of workers.

• Proceedings of the Safety Management and Science Conference
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• 2011.11a
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• pp.433-448
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• 2011

In this paper, low birth rate due to aging in adramatic increase in the older population diversified modern social welfare services to meet the demand of the Ubiquitous Network approach to the introduction of social welfare through feasibility studies, modern social welfare facilities for the operation of the future direction and development of alternative to evaluate the present.

• International Journal of Railway
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• v.6 no.1
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• pp.13-25
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• 2013

Railpad prevents damage of the tie and ballast by reducing the impact and high frequency vibration, which occurs when a vehicle load transfers to a tie. But elasticity of the railpad can decrease under vehicle load and over usable period. If that happens, railpad will become stiffer. Increase in stiffness of the railpad also translates into a rise in track maintenance cost because it accelerates the damage of the track. In this study, accelerated heat ageing test was performed to predict an expectable lifetime of the railpad. As a result, it was predicted to be about sixteen years at $25^{\circ}C$ that life time of railpad using NR rubber from Arrhenius relationship. Also, it was predicted to be about thirty-two days at $100^{\circ}C$. At this time, a standard rate of thickness change is approximately within 12%.

• Research in Community and Public Health Nursing
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• v.26 no.4
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• pp.372-379
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• 2015

Purpose: This research was conducted to examine the successful aging and identify factors influencing successful aging in the Korean elderly. Methods: The subjects were 4,507 elders and data were collected from the 4th Korean Longitudinal Study of Ageing in 2012. The data were analyzed using frequencies, weighted percentage, ${\chi}^2$ test, and logistic regression. Results: The results of this study showed that 19.6% of the participants were categorized to successful aging. The domains of the absence of disease and disability and maintaining physical and mental functioning showed a high rate of achievement, while the domain of active engagement with life showed a low rate of achievement compared to others. Successful aging was influenced by gender, age, subjective economic status, subjective health status, and family support, particularly spouse's support. Conclusion: Intervention programs to increase the prevalence of successful aging are required. Especially programs for strengthening spouse's support and enhancing subjective health status are required.

• Proceeding of Spring/Autumn Annual Conference of KHA
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• 2008.11a
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• pp.235-240
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• 2008

When rate of stated and public owned demesne in residential environment improvement is low under the limited resources of revenues, the new infrastructure for the maintenance of the existing estate has increased land reduction rate thus the place where lot of small estate find it difficult to accept as the feature of residential environment improvement. Although 'Diffusion model of residential environment improvement' which designed to overcome existing residential environment improvement, is middle of progress, there is not any suggestion made to solve problem caused by short of estate in order to maintain small estate and total Infrastructure. In feature of resident, we also notice ageing not only facilities and building. 'Elderly housing' can be presented as an alternative living style to solve housing and elderly matter which are caused by accumulation of individual estate and aging at once. Therefore, this research identifies resident's perception about elderly housing and recognizes task and potentialities that has to be solved in order to apply virtually to residential environment improvement.

• Health Policy and Management
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• v.28 no.3
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• pp.233-239
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• 2018

A rapid decrease of total fertility rate to 1.08 in 2005 prompted the Korean government to plan and implement a '5-year plan for ageing society and population policy' starting from 2006. The 1st and 2nd 5-year plans had not shown any discernible impact on the fertility and the 3rd 5-year plan was launched in 2016. However, the fertility rate is going down further. The author reviewed the contents and assessment reports of the fertility promotion plan to suggest ideas for complementing the shortcomings of it. Author defined the major determinants of marriage and child birth as philosophy, politics, sense of value, social norm, culture, healthcare, and education. The plan was examined in view of these determinants. Transformation of Korea from an agricultural society to an industrialized society in a short period of time had brought about changes in most of the determinants of marriage and child birth; in particular philosophy and sense of value. These aspects were not put into consideration in the plan. Author suggested to launch a social education program for the general public to establish a sound philosophy of life, reform the sense of value on family, child birth and education, and cultivate the skill to draw a consensus through discussions on the social issues. A special program to promote marriage of women at the optimum age for child birth was proposed. The government should implement well balanced policy for economic development and labor. Multidisciplinary approach was recommended for these tasks.

• Journal of the Korean Ceramic Society
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• v.45 no.11
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• pp.725-733
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• 2008

In this study the preparation method of the spherical ADU droplets, intermediate compound of a HTGR nuclear fuel, was detailed-reviewed and then, the characteristics on an ageing and a washing steps among the wet process and the thermal treatment process on the died-ADU${\rightarrow}UO_3$ conversion with the high temperature furnaces were studied. The key parameters for spherical droplets forming are a precise control of feed rate and a suitable viscosity value selection of a broth solution. Also, a harmony of vibrating frequency and amplitude of a vibration dropping system are important factor. In our case, an uranium concentration is $0.5{\sim}0.7mol/l$, viscosity is $50{\sim}80$ centi-Poise, vibration frequency is about 100Hz. In thermal treatment for no crack spherical $UO_3$ particle, the heating rate in the calcination must be operated below $2^{\circ}C$/min, in air atmosphere.