• Journal of the Korea Concrete Institute
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• v.18 no.6 s.96
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• pp.769-776
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• 2006

Recently, owing to the development of industry and the improvement of building techniques, concrete structures are becoming larger and higher. In hardening of these large connote structures, the heat of hydration gives rise to considerable thermal stress depending on the size and environmental condition of concrete, which might cause thermal cracking. Especially, the crack may cause severe damage to the safety and the durability of concrete structure. This study investigates the thermal properties of concrete according to several binder conditions, such as OPC, Belite rich cement(BRC), slag cement(SC), blast furnace slag(B) added cement fly ash(F) added cement and blast-furnace-slag and fly ash added cement. As a result of this study, the properly of concrete is most better BRC than others, and fly ash(25%) added cement and BFS(35%)-fly ash(15%) added cement gets superior effect in the control of heat hydration. But synthetically considered properties of concrete, workablity, strength heat hydration, etc, it is more effective to use mineral admixture. Especially, to be used Blast Furnace slag is more effective.

• Composites Research
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• v.16 no.3
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• pp.75-84
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• 2003

The purpose of this study is to investigate the wear properties of Saffil/Al, Saffil/A12O3/Al and Saffil/SiC/Al hybrid metal matrix composites fabricated by squeeze casting method. Wear tests were done on a pin-on-disk friction and wear tester under both dry and lubricated conditions. The wear properties of the three composites were evaluated in many respects. The effects of Saffil fibers, $\textrm{Al}_2\textrm{O}_3$ particles and SiC particles on the wear behavior of the composites were investigated. Wear mechanisms were analyzed by observing the worn surfaces of the composites. The variation of coefficient of friction(COF) during the wear process was recorded by using a computer. Under dry sliding condition, Saffil/SiC/Al showed the best wear resistance under high temperature and high load, while the wear resistances of Saffil/Al and Saffi1/$\textrm{Al}_2\textrm{O}_3$/Al were very similar. Under dry sliding condition, the dominant wear mechanism was abrasive wear under mild load and room temperature, and the dominant wear mechanism changed to adhesive wear as load or temperature increased. Molten wear occurred at high temperature. Compared with the dry sliding condition, all three composites showed excellent wear resistance when lubricated by liquid paraffin. Under lubricated condition, Saffil/Al showed the best wear resistance among them, and its COF value was the smallest. The dominant wear mechanism of the composites under lubricated condition was microploughing, but microcracking also occurred to them to different extents.

• Journal of the Korea Concrete Institute
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• v.29 no.1
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• pp.23-32
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• 2017

The joints between precast PSC slabs of the intermediate road slab in double deck tunnel are inevitably generated in the road traffic vehicle traveling direction. Therefore, it is important to make the behavior of parts on the joint in one piece. The imtermediate road slab system of double deck tunnel in great depth proposed in this study will be constructed with precast PSC slab in order to minimize the construction period. And the joint connection between the precast slab has been developed in two methods: the 'Transverse tendon reinforcement method' and 'High strength bolts connection method'. Also, the experiments were performed for the full scale model in order to evaluate the performance of the intermediate road deck slab with two type joints systems, the structural stability was verified through the F.E.M analsysis. The results of static loading test and F.E.M analysis investigated a very stable behavior of intermediate road deck slab in double deck tunnel applying the joint methods developed in this study, in the cracks and deflections to satisfy the design standards of Highway Roads Bridges (2011), it was determined that there is no problem even servicebility.

• Resources Recycling
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• v.29 no.3
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• pp.11-23
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• 2020

This study aims to investigate breakage and liberation characteristics of iron ore from Shinyemi mine, Jeongseon by ball mill. Parameters of breakage functions for three grade samples of iron ore were obtained using single-sized-feed breakage test and back-calculation based on nonlinear programming. The results showed that with the increase in the grade of iron ore, the breakage rate factor decrease whereas the particle size sensitivity decreases. This results from retardation of microcrack-propagation by magnetite grain in the ore. Breakage distribution analysis showed that the breakage mechanism appear to be impact fracture dominant with the increase of grade owing to the stress distribution effect by magnetite grain. Degree of liberation (DOL) increased with the increase in grade and decrease in particle size, respectively. Using the breakage function and size-DOL relationship, a model that can predict time-dependent-DOL is established. When scale-up factors from operating condition are available, the model is expected to be capable of predicting size and DOL with time in actual mining process.

• Journal of Korean Tunnelling and Underground Space Association
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• v.21 no.5
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• pp.657-673
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• 2019

A monitoring method based on acoustic emission (AE) sensor has been widely used to evaluate the damage of structures in underground rock. The acoustic emission signal generated from cracking in material is analyzed as various acoustic emission parameters in time and frequency domain. To investigate from initial crack generation to final failure of rock material, it is important to understand the characteristics of acoustic emission parameters according to the stress ratio and rock strength. In this study, uniaxial compression tests were performed using very strong and weak rock specimen in order to investigate the acoustic emission parameters when the failure of specimen occurred. In the results of experimental tests, the event, root-mean-square (RMS) voltage, amplitude, and absolute energy of very strong rock specimen were larger than those of the weak rock specimen with an increase of stress ratio. In addition, the acoustic emission parameters related in frequency were more affected by specification (e.g., operation and resonant frequency) of sensors than the stress ratio or rock strength. It is expected that this study may be meaningful for evaluating the damage of underground rock when the health monitoring based on the acoustic emission technique will be performed.

• Land and Housing Review
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• v.13 no.1
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• pp.141-150
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• 2022

Responding to the increasing demand for research on seismic resistance of structures triggered by a large-scale earthquake in Korea, the Ministry of the Interior and Safety revised the typical application of the existing seismic design standards with the national seismic performance target enhanced. Therefore, in this paper, the dam body of the aged Test-Bed and the penstock with fluid were modeled by the three-dimensional finite element method by introducing several variables. The current seismic design standard law confirmed the safety of the dam structure and penstock against seismic waves. As a result of the 3D finite element analysis, the stress change due to the water impact of the penstock was minimal, and it was confirmed that the effect of the hydraulic pressure was more significant than the water impact in the earthquake situation. When the hydrostatic pressure is in the form of SPH, it was analyzed that the motion of the fluid and the location of stress caused by the earthquake can be effectively represented, and it will be easier to analyze the weak part. As a result of the analysis, which considers penstock's corrosion, the degree of stress dispersion gets smaller because the penstock is embedded in the body. The stress result is minimal, less than 1% of the yield stress of the steel. In addition, although there is a possibility of micro-tensile cracks occurring in the inlet of the dam, it has not been shown to have a significant effect on the stress increa.

• Proceedings of the Korean Society of Organic Agriculture Conference
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• 2009.12a
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• pp.287-287
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• 2009

우리나라의 시설재배면적은 51,237ha에 이르며 수경재배 면적을 제외하면 대부분 경운재배를 하고 있는 실정이다. 경운 작업은 대형 농기구를 이용하여 경운하기 때문에 시설내 토양 입자가 단립으로 잘게 부서지며 대형농기구로 인하여 토양이 답압되고 경운층 아래 경반층이 형성되어 뿌리 발육과 배수 불량의 원인을 제공하게 된다. 경운은 기존에 설치되어 있는 관수시설과 지주, 멀칭을 제거한 후 유기물을 투입하고 2~3회 경운작업 후 다시 소형농기구를 이용하여 이랑을 조성한다. 그리고 제거된 관수시설, 멀칭, 지주를 다시 설치하여야 하기 때문에 시설의 경운재배는 가장 고통스러운 악성노동을 수반하게 된다. 따라서 본 시험에서는 시설 고추 유기재배 시 무경운재배 효과에 대하여 검토하고자 전남 나주시 남평읍 평산리 "JD 중동통 미사질양토"에서 시험을 수행하였다. 2009년 3월 11일 "녹광" 고추 품종을 재식 거리 135${\times}$38cm로 정식하여 7월 27일까지 재배한 후, 시험포를 1/2로 나누어 트렉터를 이용하여 경운작업을 실시하고 2009년 8월 1일 억제작형으로 "녹광" 고추 품종을 정식하였다. 그리고 나머지 시험포 1/2은 전작물을 재배한 이랑에 경운작업을 생략하고 전작물 고추의 식물체는 지제부를 절단하여 분해되도록 고랑을 피복하였으며, 고추 포기와 포기 사이에 무경운으로 고추를 정식하여 시험을 수행하였다. 고추 정식 전 7월 30일에 경운 시험포에 10a당 29톤의 물을 관수하였으며, 무경운 시험포에는 10a당 48톤의 물을 관수하고, 관수 2일 후 시험포의 습도와 이랑에 발생되는 균열수를 조사하였다. 이랑의 수분함량은 표토 0.23%, 토양 30cm 깊이의 수분함량은 0.18%로 경운방법에 따라서 차이가 없었으나 토양 20cm 깊이의 수분함량은 경운은 0.25%, 무경운은 0.14%로 경운재배 토양에 비하여 뿌리의 주요 분포지역인 작토층의 수분함량이 44% 정도 낮았다. 그리고 경운재배 이랑에서는 7~35cm 정도 되는 균열이 m당 22개정도 발생되었으나 무경운에서는 관찰되지 않았다. 시설 토양의 생물다양성 지표가 되는 미소동물의 분포를 조사한(9월 16일) 결과 경운재배 토양에서는 보리톡톡기 등 8종 97개체가, 무경운 토양에서는 10종 101개체가 포획되었다. 경운 방법에 따른 시설 유기재배 고추의 수확과수는 주당 139~141과, 수량은 1,367~1,431g/주가 수확되고 10a당 수량은 경운재배가 2,790kg, 무경운재배는 2,666kg이 생산되어 경운방법에 따른 수량 차는 인정되지 않았다. 경운방법에 따른 경영비를 분석한 결과 무경운은 경운재배에 비하여 10a당 유기질 비료비 178천원, 대농구상각비 211천원, 노력비 261천원의 절감으로 경운재배 경영비 4,815천원/10a 대비 약 14%의 경영비가 절감되었다. 그리고 작기마다 반복되는 경운작업과 관수시설, 멀칭, 지주설치 작업을 1회 설치 작업으로 연속사용이 가능하여 시설재배에서 가장 고통스러운 악성노동의 회피가 가능하였다.