• Architectural research
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• 제14권4호
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• pp.153-161
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• 2012

This paper presents an integrated procedure to predict the temperature and moisture distributions in hardening concrete considering the effects of temperature and aging. The degree of hydration is employed as a fundamental parameter to evaluate hydro-thermal-mechanical properties of hardening concrete. The temperature history and temperature distribution in hardening concrete is evaluated by combining cement hydration model with three-dimensional finite element thermal analysis. On the other hand, the influences of both self-desiccation and moisture diffusion on variation of relative humidity are considered. The self-desiccation is evaluated by using a semi-empirical expression with desorption isotherm and degree of hydration. The moisture diffusivity is expressed as a function of degree of hydration and current relative humidity. The proposed procedure is verified with experimental results and can be used to evaluate the early-age crack of hardening concrete.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2012년도 추계 학술논문 발표대회
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• pp.255-257
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• 2012

Epoxy resin without any hardener can harden in the presence of hydroxide ions in cement mortars and concretes at ambient temperature. The purpose of present study is to examine the hardening properties of hardener-free epoxy-modified mortars by curing conditions. The hardener-free epoxy-modified mortars using diglycidyl ether of A epoxy resin are prepared with various polymer-cement ratios, and subjected to initial moist/dry curing, initial steam(90℃) curing, initial steam/heat(80℃, 100℃) curing.As a result, degree of hardening of epoxy resin in initial moist/dry cured, initial steam cured and initial steam/heat(80℃) cured hardener-free epoxy-modified mortars is decreased with increasing polymer-cement ratio. However, it is markedly improved with additional dry-curing periods. On the other hand, regardless of the polymer-cement ratio and dry curing periods, degree of hardening of hardener-free epoxy-modified mortars with initial steam/heat(100℃) cure is over 95%.

• 열처리공학회지
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• 제8권1호
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• pp.24-31
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• 1995

Heat flow equation and FEM have been used to calculate the hardening section of material in laser transformation hardening. SCM440 used as the diesel engine piston of vessel has been hardened by a $CO_2$ laser with the wavelength of $10.6{\mu}m$. The specimens were inclined from 0 to 70 degree to investigate the characteristics of laser hardening. The geometrical factor of heat flow equation affects the size of hardening area. The case width decreased with increasing travel speed and the case width increased with increasing inclined angle. Maximum case depth was achieved about 1.0mm and maximum hardness of laser hardened area was of 2.8 times than that of base metal. Experimental data show good agreement with the theoretical calculations for given laser hardening conditions.

• 한국표면공학회지
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• 제46권1호
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• pp.48-53
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• 2013

In the present work, it was investigated a behavior of hydrogen embrittlement at the subsurface zones of 590 DP steels by using the micro-Vickers hardness test. The micro-Vickers hardnessess of DP steels were measured to evaluate the degree of embrittlement as the effective hardening depths of subsurface zones with hydrogen charging conditions. The results showed that the distributions of micro-Vickers hardness in width varied from maximum hardness 239.5 Hv to minimum hardness 174 Hv, while the depth of effective hardening layer at the subsurface zones of DP steels was from $320{\mu}m$ to $460{\mu}m$ with hydrogen charging conditions, respectively. It was proposed that the distribution of microhardness be used as the evaluation index of the degree of embrittlement. But the variations of martensite volume fractions were not affected along depth of hardening at the same changing time, hydrogen charging times were appeared as an effective factor of the degree of embrittlement. Therefore, the micro-Vickers hardness test is an attractive tool for evaluation of hydrogen embrittlement at the subsurface zones of these DP steels.

• 열처리공학회지
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• 제34권4호
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• pp.179-184
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• 2021

Two types of secondary hardening martensitic steels, 10Co-14Ni and 6Co-5Ni, were produced by vacuum induction melting to investigate the effect of ausforming process on mechanical properties. According to the results of present study, the alloy samples ausformed at low temperature indicated a rather low hardness level in overall aging time despite the refinement of martensite lath width. As the result can closely be related with the presence of primary carbides precipitated within the initial austenite matrix, we confirmed that, in ultrahigh strength secondary hardening martensitic alloy steels, the ausforming process can rather limit the degree of secondary hardening during the subsequent aging treatment.

• Earthquakes and Structures
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• 제14권5호
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• pp.459-465
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• 2018

Reducing response of buildings during earthquakes by mass dampers, has been examined in many articles and books. Nowadays, many researchers are trying to realistically examine this type of dampers by new methods of performance. In this paper, for the better study of tuned mass damper (TMD), two schematic models are presented for a passive TMD with softening stiffness (softening TMD) and a passive TMD with hardening stiffness (hardening TMD). Then by modeling and analysis of the damper on a single degree of freedom (SDOF) structure and an 11-story steel building, the dampers performance was evaluated. State space was used for damper and structure modeling and to solve nonlinear equations, the Newton-Raphson method was used. The results show that when the structure is subjected to the Chi-Chi earthquake, response of the sixth floor in the system without TMD reduces 54.0% in comparison to the structure with softening TMD. This percentage of reduction for hardening TMD is 55.0%. Also for the Tabas earthquake, reduction in the RMS acceleration of the sixth floor in the system with hardening TMD is 96.2% more than the structure without TMD. This percentage of reduction for hardening TMD is 96.3%.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2014년도 추계 학술논문 발표대회
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• pp.13-14
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• 2014

Ultra high performance concrete (UHPC) consists of cement, silica fume (SF), sand, fibers, water and superplasticizer. Typical water/binder-ratios are 0.15-0.20 with 20-30% of silica fume. The development off properties of hardening UHPC relates with both hydration of cement and pozzolanic reaction of silicafume. In this paper, by considering the production of calcium hydroxide in cement hydration and its consumption in the pozzolanic reaction, a numerical model is proposed to simulate the hydration of UHPC. The degree of hydration of cement and degree of reaction of silica fume are obtained as accompanied results from the proposed hydration model. The properties of hardening UHPC, such as degree of hydration of cement, calcium hydroxide contents, and compressive strength, are predicted from the contribution of cement hydration and pozzolanic reaction. The proposed model is verified through experimental data on concrete with different water-to-binder ratios and silica fume substitution ratios.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2015년도 춘계 학술논문 발표대회
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• pp.50-51
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• 2015

In marine and coastal environments, penetration of chloride ions is one of the main mechanisms causing concrete reinforcement corrosion. Currently, most of experimental investigations about submerged penetration of chloride ions are started after the four weeks standard curing of concrete. The further hydration of cement and reduction of chloride diffusivity during submerged penetration period are ignored. To overcome this weak point, this paper presents a numerical procedure to analyze simultaneously cement hydration reaction and chloride ion penetration process. First, using a cement hydration model, degree of hydration and phase volume fractions of hardening concrete are determined. Second, the dependences of chloride diffusivity and chloride binding capacity on age of concrete are clarified. Third, chloride profiles in hardening concrete are calculated. The proposed numerical procedure is verified by using chloride penetration test results of concrete with different mixing proportions.

• 한국작물학회지
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• 제39권3호
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• pp.205-210
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• 1994

최근 담수직파 재배양식중 승용형 골뿌림 파종기를 이용하여 파종골을 작성, 이와 동시에 종자를 파종하고, 생육기간동안 골이 자연적으로 매몰됨으로서 도체가 지지력을 가져 직파재배시 단점중의 하나인 도복을 경감시킬 수 있다는데 근거를 두고 시험연구가 급속히 진행되고 있는 무논 골 뿌림 재배법 확립의 일환으로, 먼저 초기 입묘와 밀접한 관계가 있는 파종전 토양굳힘정도, 파종 골 깊이, 그리고 파종후 담수시기 구명을 위하여 시험한 결과는 아래와 같다. 1. 파종전 토양의 굳힘정도는 파종시 종자의 매몰정도, 파종후 담수시 종자 부유상태 및 생육기간동안 골 매몰로 인한 줄기매몰심도등을 고려할때 경운정지후 낙수하여 3일정도 굳힌상태 즉, 115g의 원추관입심이 6~7cm정도인 상태가 적절하였다. 2. 파종골 깊이별 최고 분얼기에 조사한 토양매몰정도는 4~6cm심도의 경우 3~4cm정도의 토양매몰이 이루어졌으며, 입묘율은 골 깊이가 깊을수록 떨어지는 경향이었다. 표면조파(0cm)의 경우 부묘가 발생되었으며, 골 깊이별 뿌리 분포비율은 파종심도가 낮을수록 표층의 뿌리 분포 비율이 높고, 도복정도 역시 8 정도로 매우 높아서, 줄기 매몰심도 및 도복정도 그리고 수량성으로 볼때 파종골 깊이는 4cm정도가 적당하였다. 3. 파종후 담수시기가 늦어질수록 입묘율이 떨어졌으며, $m^2$ 당수수의 확보 역시 적어서 담수시기는 파종직후 담수가 바람직 하였다.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2012년도 춘계 학술논문 발표대회
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• pp.263-264
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• 2012

The purpose of present study is to examine the long-term strength improvement of hardener-free epoxy-modified mortars with steam curing. As a result, strength improvement of hardener-free epoxy-modified mortars is markedly improved with increasing of air-dry curing period. This is improved by markedly increase the degree of hardening of the hardener-free epoxy resin in the epoxy-modified mortars with additional air-dry curing period.