• Journal of the Korea Institute of Building Construction
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• v.4 no.4
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• pp.87-94
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• 2004

As the bentonite is main material to prevent from collapse of drilling hole at underground excavation works, it is increased using quantity on construction industry day by day. But, the discarded bentonite that is over using at underground excavation works is caused various enviromental trouble as soil and water pollution est. Therefore, this study aims to propose a foundamental report for pozzolan reaction of discarded Bentonite powder by heat-treatment and cooling as concrete mineral admixture. To find out pozzolan reaction ability of discarded Bentonite powder by indirect cooling & cooling using of water after heat-treatment, the experiments are excuted flow test & compressive strength on age of mortar using discarded Bentonite powder. As a result of this study, discarded Bentonite powder can be utilized as concrete mineral admixture by heat-treatment and especially, pozzolan reaction ability of discarded Bentonite powder is superior to the situation of 600℃. 60min ＆amp; cooling using of water.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2004.05a
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• pp.41-44
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• 2004

Recently, in the case of domestic, for all that the deterioration environment about the carbonation of reinforced concrete structures is accelerated, systematic diagnosis and researches are not completed. And the selection techniques of repair material and method used under the situation that the indicator and the performance evaluation method are nor established are dependant on existing experience. Therefore, the purpose of this study is intend to present fundamental data for the reasonable selection of repair material and method. durability design and longevity on the deteriorated reinforced concrete structures, through computing the carbonation depth and velocity coefficient by accelerating carbonation test under various accelerating conditions and investigating the application of carbonation evaluation method. The results of this study are as follow; The resistances to carbonation are increased when the W/C ratio if lower and the treatment of surface coating is executed. And the carbonation depth and velocity coefficient according to accelerating carbonation test conditions are increased when the conditions of temperature, relative humidity and $CO_2$density are higher individually.

• Journal of the Korea Institute of Building Construction
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• v.6 no.3 s.21
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• pp.99-105
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• 2006

In this paper, the estimation of compressive strength of concrete incorporating fly ash subjected to high temperature is discussed. Ordinary Portland cement and fly ash cement(30% of fly ash) were used, respectively. Water to binder ration ranging from 30% to 60% and curing temperature ranging from $20^{\circ}C{\sim}65^{\circ}C$ were also adopted for the experimental parameters. According to results, at the high temperature, FAC had higher strength development at early age than OPC concrete and it kept its high strength development at later age due to accelerated pozzolanic reaction subjected to high temperature. For strength estimation, Logistic model based on maturity equation and Carino model based on equivalent age were applied to verify the availability of estimation model. It shows that fair agreements between calculated values and measured values were obtained evaluating compressive strength with logistic curve. The application of logistic model at high temperature had remarkable deviations in the same maturity. Whereas, the application of Carino model showed good agreements between calculated values and measured ones regardless of type of cement and W/B. However, some correction factors should be considered to enhance the accuracy of strength estimation of concrete.

• Journal of the Korean Geosynthetics Society
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• v.7 no.2
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• pp.15-21
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• 2008

The advantages of prefabricated vertical drains over conventional sand drains include their relatively low costs, less disturbance to the soil mass, the easinees of installation, and their flexibility which ensures the integrity of the drains during installation. This study tested the change of discharge capacities with respect to the hydraulic gradients for each lateral pressure. From the test results, as increases the overburden pressure, the clay soil is being consolidated, and also lateral pressure to the PVD specimen is increased. Therefore, the discharge capacity is decreased. The size of opening space in the core of PVDs is proportionally related to the discharge capacity. The numerical analysis was performed with utilizing computer simulation with considering field conditions. The results of numerical analysis are compared well with the field measurements.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2009.04a
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• pp.392-395
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• 2009

응답면 기법을 활용하여 댐구조물과 같은 사회간접자본 시설물의 파괴확률을 구할 수 있다. 본 위험성 평가과정에서 응답면기법으로 구성한 한계상태 방정식을 유전자알고리즘의 적합도 방정식으로 사용하면, 핵심타입이나 지반종류, 지반다짐정도 등의 입력설계변수의 최적화 과정 속도를 더욱 신속화 시킬 수 있다. 제안된 응답면 기법과 유전자알고리즘의 복합해석기법은 신뢰성기반 최적화프로그램으로 기존의 유전자알고리즘의 수렴속도를 더욱 빠르게 하여주고, 특히 입력변수의 상하한계가 불확실한 경우에도 만족스러운 수렴성을 보장하여준다. 한계상태 방정식의 목표신뢰도 지수를 변화시켜면 해당하는 입력변수의 최적값을 출력하여주므로, 입력변수의 제약조건에 가격함수와 같은 가중치를 벌칙함수로 부여하면 가격최적화 프로그램으로 작용하게 되며, 시설물 운영자에게는 목표신뢰도에 대한 유지관리 기법과 정도를 의사결정 할 수 있도록 하여주는 기능을 가지게 된다. 조사된 많은 댐구조물의 파괴모드가 시간에 독립적으로 시공중 또는 시공완료 후 5년이내에 다수 발생하는바, 파괴모드를 조사하고 중요한 파괴모드인 파이핑 현상에 대해서 파괴확률을 계산하고 최적유지관리를 위한 개선된 유전자알고리즘 최적화 연산을 수행하였다. 기존 댐구조물과 같이 설계변수와 하중의 변동성을 알기가 어려운 경우에 유지관리비용 최소화를 위해서 본 제안 프로그램의 확장된 버젼은 중요한 기준을 제시하여줄 것으로 기대한다.

• Journal of the Korea Construction Safety Engineering Association
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• s.45
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• pp.60-70
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• 2008

Mechanized tunnelling by TBMs has been extensively adopted for last two decades. Nevertheless, only few case histories have been reported. Unlike NATM tunnels, the case histories of the weak zone have been seldom reported for the mechanized tunnelling, even in the other countries. In this study, a collapse of TBM tunnel occurred in the severely altered weak rock zones between volcaniclastic rocks and granitic rocks was briefly described. A systematic geotechnical investigation, which was performed to examine the cause of the collapse, was carried out at the site and then characteristics of the rocks in the zones were evaluated. Moreover, This study propose a guide line of estimateing the possibility of collapse in TBM tunnels through comparing experimental results with surveying results of general rocks.

• Journal of the Korea Institute of Building Construction
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• v.5 no.4 s.18
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• pp.115-120
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• 2005

In recent years, polymer-modified mortars using polymer dispersions have been widely used as finish and repair materials in the construction industry because of their excellent properties compares to those of ordinary cement mortar. Especially, the adhesion improvement of ordinary cement mortar and concrete has attracted a great deal of attention from researchers, and several unique and simply applicable techniques for the adhesion improvement have been developed. The purpose of this study is to evaluate the abrasion resistance of polymer-modified mortar according various curing methods. The polymer-modified mortar are prepared with various polymer-cement ratios, and are subjected to three curing methods such as dry rure, standard cure and freezing and thawing cure after two curing methods, and then tested for abrasion. From the test results, the polymer-modified mortars with various polymer-cement ratios have some superior abrasion resistance compared with plain mortar. The abrasion resistance of polymer-modified mortars increase with an increase in the polymer-cement ratio, and is better under water cure than any other curing methods. It is concluded that the abrasion resistance of cement mortar is markedly improved by modifying of polymer dispersion.

• Journal of the Korea Institute of Building Construction
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• v.7 no.4
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• pp.145-151
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• 2007

In this paper, tests are carried out in order to investigate the strength development of concrete under various binder types, W/B and curing temperature ranged from $5{\sim}20^{\circ}C$. Fly ash and blast furnace slag were incorporated by as much as 30%, respectively. Strength development of concrete are estimated using Logistic model and strength ratio of concrete at 28days to that at early age are also investigated. According to experimental results, it is found that good agreements are obtained between measured values and calculated ones using logistic model below $20^{\circ}C$. Strength ratio of concrete at 28days to that at early age increases in case W/B decreases and curing temperature increases. Tables and graphs for strength ratio of concrete are provided in this paper. It is capable of obtaining and predicting the periods to attain design strength by considering increment factor of strength easily with the table and graphs presented in this paper. This paper presents the reference data to decide removal time of form, time to reach target strength and strength inspection of remicon whether the test specimens meet the specified criteria of compressive strength. Multi regression models with respect to the relationship between 7days compressive strength and 28 days compressive strength depending on W/B and admixture types are presented.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2012.11a
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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%.

• Tunnel and Underground Space
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• v.20 no.3
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• pp.131-144
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• 2010

The design and construction of tunnels has been followed an large parallel tunnels with a small clearance because of the various conditions. Rock pillar between each single tunnel is supposed to be under heavy load by rock mass. The stability of pillar is very important for the ensure the stability of the large parallel tunnels. In this study, the analysis of stress state of pillar at various construction cases is reviewed to investigate the mechanical behaviour of tunnels and stability of the pillar.