• Computers and Concrete
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• 제26권5호
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• pp.429-438
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• 2020

To shorten the construction times of nuclear facility structures, three high-strength concrete mixtures were developed with specific consideration given to their curing temperatures, their economic efficiency, and the practicality of their quality control. This study was conducted to examine the temperature rise profiles of these three concrete mixtures and the potential for early-age thermal cracking in the primary containment vessel of a nuclear reactor with a wall thickness of 1200 mm. The one-layer placement height of the concrete for the primary containment vessel was increased from the conventional 3 m to 3.5 m. A nonlinear finite element analysis (FEA) was conducted using the thermal properties of concrete determined from the isothermal hydration and adiabatic hydration tests, and tuned through comparisons made with temperature rise profiles obtained for 1200-mm-thick mock-up wall specimens cured at temperatures of 5, 20, and 35℃. The hydration heat performance of the three concrete mixtures and their potential to produce thermal cracking in nuclear facilities indicate that the mixtures have considerable potential for practical application to the primary containment vessel of a nuclear reactor at various curing temperatures, fulfilling the minimum requirements of the ACI 301 and minimizing the likelihood of the occurrence of thermal cracks.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2017년도 춘계 학술논문 발표대회
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• pp.230-231
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• 2017

The addition of a limestone filler(LF) to fill into the voids between cement and aggregate particles can reduce the cementitious paste volume. This paper aim to evaluate the influence of LF contents on the hydration kinetics and compressive strength. Hydration kinetics were evaluate using heat of hydration, ignition loss and thermal analysis. The heat of hydration was measured using Isothermal Calorimetry. The degree of hydration was measured using ignition loss. Hydration product analysis was carried out by Thermal Gravimetric and Differential Thermal Analysis. The results show that the addition of LF reduces not only the initial setting time and heat of hydration peak, also degree of hydration and rate of strength development at early age increase with the addition of LF. It can be concluded the LF fills the pore between cement particles due to formation of carboaluminate, which may accelerate the setting of cement pastes.

• 한국산업융합학회 논문집
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• 제8권3호
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• pp.169-176
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• 2005

The purpose of this study is to develop the high strength crushed sand concrete in conditions of water binder ratios of 25, 30, 35% and blast-furnace slag substitutions of 0, 15, 30, 45%. Additionally, in case of water binder ratio of 30%, the maximum size of coarse aggregate is two kinds of 13, 19 mm. The conclusions of this study are as follows ; 1. The compressive strength appeared lower in early age as compared with that of plain concrete according to increasing of the blast-furnace slag substitution. But, the compressive strength was respectively 5, 6, 10% larger than that of plain concrete in case of 25, 30, 35% water binder ratios, 28 days, 30% blast-furnace slag substitution and 19mm coarse aggregate. 2. According to increasing of the blast-furnace slag substitution, the modulus of elasticity and the tensile strength of concrete increased. 3. The length change by the shrinkage increased when the larger coarse aggregate was used, and decreased according to higher blast-furnace slag substitution.

• 콘크리트학회지
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• 제10권5호
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• pp.81-87
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• 1998

최근 들어 교통난 해소를 위한 도로확폭 공사나 파일항타 및 발파 등의 공사가 많이 진행되고 있으며, 이러한 경우 진동의 영향으로 콘크리트의 품질 저하에 영향을 미칠 것으로 예상된다. 이에 따라 본 연구에서는 진동과 굳지 않은 콘크리트에 미치는 영향을 평가하기 위하여 실험변수를 진동속도, 진동발생점등으로 나누어, 콘크리트의 압축강도, 부착강도를 측정하였다. 또한 응결시간을 측정하여 외부 진동용인이 응력에 미치는 영향을 평가하였다. 진동속도는 0.25cm/sec ~4.2cm/sec까지 변화시켰고, 진동가력시점은 타설 직후(0시간)부터 타설 후 2, 4, 6, 12 시간 후 에 진동을 가하였다. 본 연구의 실험 결과 진동속도 0.25cm/sec 에서는 압축 강도와 부착강도가 증가하는 반면에 진동속도 0.5cm/sec 이상에서는 압축강도는 5~12% 정도 감소하고 부착강도도 이와 유사하게 감소하는 것으로나타나고 있다. 응결시간은 0.25cm/sec의 작은 진동에서는 영향이 거의 없으나 0.5cm/sec 이상에서는 타설 직후의 진동시 응결시간이 다소 빨라지는 것으로 나타났다. 본 연구 결과, 양생초기 콘크리트의 진동 허용치는 약 0.3~0.4cm/sec 로 나타나고 있으며, 이것은 앞으로 실제 구조물의 시공시 진동규제치로서 하나의 유용한 자료가 될 수 있을 것으로 사료된다.

• Structural Engineering and Mechanics
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• 제45권6호
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• pp.837-851
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• 2013

In construction industry, strength is a primary criterion in selecting a concrete for a particular application. The concrete used for construction gains strength over a long period of time after pouring the concrete. The characteristic strength of concrete is defined as the compressive strength of a sample that has been aged for 28 days. Neither waiting for 28 days for such a test would serve the rapidity of construction, nor would neglecting it serve the quality control process on concrete in large construction sites. Therefore, rapid and reliable prediction of the strength of concrete would be of great significance. On this backdrop, the method is proposed to establish a predictive relationship between properties and proportions of ingredients of concrete, compaction factor, weight of concrete cubes and strength of concrete whereby the strength of concrete can be predicted at early age. Multiple regression analysis was carried out for predicting the compressive strength of concrete containing Portland Pozolana cement using statistical analysis for the concrete data obtained from the experimental work done in this study. The multiple linear regression models yielded fairly good correlation coefficient for the prediction of compressive strength for 7, 28 and 40 days curing. The results indicate that the proposed regression models are effectively capable of evaluating the compressive strength of the concrete containing Portaland Pozolana Cement. The derived formulas are very simple, straightforward and provide an effective analysis tool accessible to practicing engineers.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2009년도 춘계 학술논문 발표대회 학계
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• pp.73-76
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• 2009

Autogenous shrinkage of high-strength mass concrete is affected high temperature history. So to evaluate autogenous shrinkage of high-strength mass concrete accurately, thermal expansion in it should be removed. In this study, compensated autogenous shrinkage was calculated after gathering thermal expansion coefficient at early age experimentally. As a result of the study. Autogenous shrinkage of mass specimen (300 ${\times}$ 300 ${\times}$ 300mm) was remarkably higher than it of standard specimen (100 ${\times}$ 100 ${\times}$ 400mm). So it was found that compensation on thermal expansion should in evaluating autogenous shrinkage of high-strength mass concrete. And this study shows results on opc and similar own contraction, if used retarder.

• Computers and Concrete
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• 제21권6호
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• pp.697-703
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• 2018

Compressive strength is one of the most important engineering properties of concrete, and testing of the compressive strength of concrete specimens is often costly and time consuming. In order to provide the time for concrete form removal, re-shoring to slab, project scheduling and quality control, it is necessary to predict the concrete strength based upon the early strength data. However, concrete compressive strength is affected by many factors, such as quality of raw materials, water cement ratio, ratio of fine aggregate to coarse aggregate, age of concrete, compaction of concrete, temperature, relative humidity and curing of concrete. The concrete compressive strength is a quite nonlinear function that changes depend on the materials used in the concrete and the time. This paper presents an adaptive neuro-fuzzy inference system (ANFIS) for the prediction of concrete compressive strength. The training of fuzzy system was performed by a hybrid method of gradient descent method and least squares algorithm, and the subtractive clustering algorithm (SCA) was utilized for optimizing the number of fuzzy rules. Experimental data on concrete compressive strength in the literature were used to validate and evaluate the performance of the proposed ANFIS model. Further, predictions from three models (the back propagation neural network model, the statistics model, and the ANFIS model) were compared with the experimental data. The results show that the proposed ANFIS model is a feasible, efficient, and accurate tool for predicting the concrete compressive strength.

• 패션비즈니스
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• 제27권2호
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• pp.1-25
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• 2023

Taq-i Bustan rock reliefs are relatively well preserved among Sassanid relics. They are considered concrete and empirically important materials for studying Sassanian culture. In these rock reliefs, inauguration of various kings and hunting scenes are depicted. Thus, kings' attire and life of the court could be discerned according to eras. The purpose of this study was to investigate Sassanian clothing styles of various social positions by analyzing their clothing depicted in rock reliefs and to improve comprehension of the culture of the Sassanian Dynasty. Methodically, literature studies and artifacts were analyzed in parallel. Data of these two insources were consolidated for comparison. Results of this study are as follows. Since the Sassanian Dynasty succeeded the Parthian Dynasty, the Parthian style of clothing pieces such as tunic and trousers appeared in their attire. Basic types of tunics and trousers did not vary according to social status or age. However, details showed differences in those aspects. In the early Sassanian Dynasty, the dressing style of Rome was adopted. Styles of tunic and trousers featured draperies with many wrinkles and shoes were worn instead of boots. Trousers were tied with laces at ankles and laces were decorated with round clasps, imitating the style used by Kushan kings to the east of Sasanians. External cultural elements were also present in costumes of the Sassanian Dynasty, which played a bridging role for cultural exchanges between Eastern and Western civilizations at the gateway of the Silk Road.

• 천문학회보
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• 제46권2호
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• pp.81.1-81.1
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• 2021

Stellar kinematics is a useful tool to understand the formation and evolution of young stellar systems. Here, we present a kinematic study of the HII region, NGC 821, using the Gaia Early Data Release 3. NGC 281 contains the open cluster IC 1590. This cluster has a core and a low-stellar density halo. We detect a pattern of cluster expansion from the Gaia proper motion vectors. Most stars radially escaping from the cluster are distributed in the halo. We measure the 1-dimensional velocity dispersion of stars in the core. The velocity dispersion (1 km/s) is comparable to the expected virial velocity dispersion of this cluster, and therefore the core is at a virial state. The core has an initial mass function shallower than that of the halo, which is indicative of mass segregation. However, there is no significant correlation between stellar masses and tangential velocities. This result suggests that the mass segregation has a primordial origin. On the other hand, it has been believed that the formation of young stars in NGC 281 West was triggered by feedback from massive stars in IC 1590. We investigate the ages of stars in the two regions, but the age difference between the two regions is not comparable to the timescale of the passage of an ionization front. Also, the proper motion vectors of the NGC 281 West stars relative to IC 1590 do not show any systematic receding motion from the cluster. Our results suggest that stars in NGC 281 West might have been formed spontaneously. In conclusion, the formation of NGC 281 can be understood in the context of hierarchical star formation model.

• Journal of Preventive Medicine and Public Health
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• 제57권4호
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• pp.319-326
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• 2024

Objectives: Despite the importance of choosing and using a valid assessment tool for fear of cancer recurrence (FCR) for early detection and interventions, the validity of the FCR inventory has yet to be thoroughly investigated in Korea. This study explored the psychometric properties of the Fear of Cancer Recurrence Inventory-Severity (FCRI-S) subscale and assessed its applicability to cancer survivors in Korea. Methods: The survey involved 93 Korean individuals who had survived cancer. The reliability of the FCRI-S subscale was assessed using Cronbach's α and composite reliability (CR). Confirmatory factor analysis (CFA), along with tests for discriminant and convergent validity, was conducted to evaluate the construct validity of the FCRI-S subscale. Results: The FCRI-S subscale showed excellent internal consistency (Cronbach's α=0.88; CR=0.89). CFA showed a good factor structure for the FCRI-S subscale, and the correlations of the FCRI-S subscale with FCR-related measures (r=0.69 to 0.80) and other psychosocial measures (r=-0.23 to 0.37) confirmed both the convergent and discriminant validity of the FCRI-S subscale. Conclusions: This study confirmed the robust psychometric characteristics of the FCRI-S subscale among cancer survivors in Korea. The use of the FCRI-S subscale would be helpful for health professionals to rapidly screen FCR levels in clinical settings.